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Modeling zinc toxicity for terrestrial invertebrates
Abstract
Acute and chronic ecotoxicity tests with zinc were performed with the earthworm Eisenia fetida, the potworm Enchytraeus albidus, and the springtail Folsomia candida. To assess the influence of the soil type on zinc toxicity for these soil invertebrates, these tests were carried out in a standard artificial soil, a sandy and a loamy field soil. Based on the results of this experimental work and data taken from literature, models were developed relating the ecotoxicity of zinc to the most important parameters controlling bioavailability: pH and cation exchange capacity. Models were developed for E. fetida and F. candida using the regression technique partial least squares projection to latent structures (PLS). Acute as well as chronic toxicity data of both organisms could be normalized on the basis of the pH and the cation exchange capacity of the test soils. For other terrestrial invertebrates, not enough data were available to develop reliable models.
... These authors attributed the differences mostly to soil texture. Lock and Janssen (2001) found higher EC 50 (nominal-based) values of Zn (ZnCl 2 ) for E. fetida in OECD soil (EC 50 = 704 mg kg −1 ) compared to field soils from Belgium (lower EC 50 value = 294 mg kg −1 ). By using their data and those from the literature, these last authors developed models to predict Zn toxicity and found pH and the CEC as the most important parameters controlling its bioavailability. ...
... The CEC seems to be the main soil property responsible for the differences in bioavailable fractions of Cu (Criel et al. 2008), while soil pH and OM were the most evidenced factors influencing the Zn bioavailability/toxicity for earthworms (Spurgeon and Hopkin 1996;Lock and Janssen 2001;Smolders et al. 2009;Heggelund et al. 2014;Świątek et al. 2017). This is consistent with our results, where higher impacts (Table 3) of Cu (Oxisol > TAS = Alfisol, based on mortality data) and Zn (Oxisol > Alfisol > TAS) occurred in the soils with lower CEC or pH/OM (respectively- Table 1) and, consequently, with higher available contents (Table 2). ...
... To establish soil screening values that can be compared between different soils, several countries/researchers have made a normalization of the ecotoxicity data (i.e., ECx) to account for differences in soil characteristics and metal bioavailability (US EPA 2005;ECHA 2008;Wang et al. 2015;Environment Agency 2022). This can be performed using ecotoxicity predictive models (Lock and Janssen 2001;Smolders et al. 2009;Oorts et al. 2021) or by applying bioavailability scores (US EPA 2005), which are generally based on normalizing factors such as soil pH, OM content, CEC, and texture. Both these strategies seem to be the best way to compare ecotoxicological data generated from Brazilian soils directly. ...
The current Brazilian copper (Cu) and zinc (Zn) prevention values (PV) for soil quality do not take into account the ecotoxicological impacts on soil organisms, which suggests these guiding values may not be protective of soil ecological
trophic levels. This study assessed the acute (mortality) and chronic toxicity (reproduction), as well as the cumulative (bioaccumulation) potential of Cu and Zn (pseudo-total and available fractions) for earthworms Eisenia andrei in a Tropical
Artificial Soil (TAS) and two tropical field soils (Oxisol and Alfisol). Toxicity data based on pseudo-total fractions were compared to PV. The Lowest Observed Effect Concentrations (LOEC) for the mortality endpoint were found at Cu and Zn
concentrations higher than their PV (60 and 300 mg kg−1, respectively), regardless of the soil type. However, concentrations lower than PV reduced the reproduction of E. andrei by 20% (compared to the controls) for Cu in all tested soils (EC20s from
31.7 to 51.2 mg kg−1) and by 50% for Zn in Oxisol and Alfisol (EC50s=225 and 283 mg kg−1, respectively). In TAS, only the EC20 (273 mg kg−1) for Zn was lower than PV. Increases of Cu in earthworm tissues occurred at concentrations higher than
PV in all tested soils (LOEC values from 70 to 107 mg kg−1). The same was observed for Zn in TAS (LOEC =497 mg kg−1), while in the field soils, the increases of Zn in earthworm tissues were lower than PV (LOEC = 131 and 259 mg kg−1 in Alfisol and Oxisol, respectively). We suggest the following: (1) The current Brazilian PV for Cu and Zn are not protective for earthworms (E. andrei) in the field soils tested; (2) PV derived from ecotoxicological assays in artificial soil cannot be representative for Brazilian field soils; (3) Using PV based on the pseudo-total fraction, without a soil-type normalizing factor, may limit the representativeness of this threshold for different soil types.
... Direct comparison of the toxicity data with those reported in the literature is difficult, because metal availability and toxicity are highly dependent on a variety of soil factors (i.e., pH, CEC, clay and organic matter content, etc.) [19,[22][23][24]. However, the study results and soil characterization data can be used to predict trends between different categories of moiety compounds for in silico modeling and assessment purposes. ...
... At pH levels between 6 and 9, Zn hydroxide will precipitate out of the soil solution, and dissolved Zn ions will form phosphate and carbonate complexes, which may influence the bioavailability and toxicity to test organisms [26,30]. Soil toxicity (EC50) for ZnCl 2 in the literature varies from 64 to 1500 mg total Zn/kg dry soil for F. candida reproduction [20,23,24,31], while effects on E. andrei reproduction have been reported at 512 mg Zn/kg dry soil [23], all of which align with the results reported in the present study for these inorganic Zn substances. ...
... At pH levels between 6 and 9, Zn hydroxide will precipitate out of the soil solution, and dissolved Zn ions will form phosphate and carbonate complexes, which may influence the bioavailability and toxicity to test organisms [26,30]. Soil toxicity (EC50) for ZnCl 2 in the literature varies from 64 to 1500 mg total Zn/kg dry soil for F. candida reproduction [20,23,24,31], while effects on E. andrei reproduction have been reported at 512 mg Zn/kg dry soil [23], all of which align with the results reported in the present study for these inorganic Zn substances. ...
Within Canada, screening-level assessments for chemical substances are required in order to determine whether the substances pose a risk to human health and/or the environment, and as appropriate, risk management strategies. In response to the volume of metal and metal-containing substances, process efficiencies were introduced using a metal moiety approach, wherein substances that contain a common metal moiety are assessed simultaneously as a group, wherein the moiety of concern would consist of the metal ion. However, for certain subgroups, such as organometals (OM) or organic metal salts (OMS), the organic moiety or parent substance may be of concern, rather than simply the metal ion. To further investigate the need for such additional consideration, zinc-containing inorganic (zinc chloride and zinc oxide) and organic (organometal: zinc diethyldithiocarbamate (Zn(DDC)2 ) and organic metal salts: zinc stearate (ZnSt) and 4-chloro-2-nitrobenzenediazonium tetrachlorozincate (BCNZ)) substances were evaluated. The toxicity of the substances were assessed using plant (Trifolium pratense and Elymus lanceolatus) and soil invertebrate (Folsomia candida and Eisenia andrei) tests in a sandy soil. Effect measures were determined based on total metal and total parent analyses (for organic substances). In general, the inorganic zinc substances were less toxic than the OM and OMS, with 50% effective concentrations ranging from 11 to > 5194 mg Zn kg(-1) dry soil. The data demonstrate the necessity for alternate approaches in the assessment of organo-metal complexes wherein the organic moieties or parent substance warrant consideration, rather than solely the metal ion. In this instance, the OM and OMS were significantly more toxic than other test substances despite their low total Zn content. This article is protected by copyright. All rights reserved.
... Earthworms show moderate sensitivity to Zn, as illustrated by our own and the results of other, 42,43 with EC 50 reproduction values in the range 200-600 mg Zn per Kg depending on the earthworm species tested and soil type. [42][43][44] The median Zn concentrations for 1083 soils measured in the UK was 61.5 mg Zn per kg, 45 suggesting that the window of essentiality between potential deficiency and toxicity for Zn may be relatively small for earthworms. ...
... Earthworms show moderate sensitivity to Zn, as illustrated by our own and the results of other, 42,43 with EC 50 reproduction values in the range 200-600 mg Zn per Kg depending on the earthworm species tested and soil type. [42][43][44] The median Zn concentrations for 1083 soils measured in the UK was 61.5 mg Zn per kg, 45 suggesting that the window of essentiality between potential deficiency and toxicity for Zn may be relatively small for earthworms. The effects of long-term metal aging in polluted soils in the field have been found to reduce metal bioavailability, which in part may mitigate the potential ecotoxicological hazard of Zn. ...
A critical question for read across of the hazards of nanomaterials is the degree to which their mechanisms of action differ from those of their bulk chemical constituents. It has been established that metal and metal oxide nanoparticles (NPs) can be accumulated by invertebrate species. Moreover, it has been hypothesised that the observed toxicity resulting on exposure to these nanomaterials is most likely to be associated with the releases of ions from external or internal dissolution leading ultimately to toxicity. However, mechanistic confirmation of the similar modes of action for metal oxide nanomaterials and metal ions in studies invertebrates are largely lacking. Therefore, here we present a toxicogenomic study using exposed individuals of the earthworm Eisenia fetida from a single genetic lineage. We compared gene expression and pathway responses through RNA-seq analysis at equitoxic concentrations (EC50 for reproduction) of ZnO NPs and ionic Zn. We found similar transcriptomic effects for both Zn forms with genetic signatures of tight control of cytosolic Zn concentrations through expression changes of genes encoding several Zn transporters. Activation and regulation of JUN, MAP and JNK kinases indicated a cellular response to the increased Zn concentrations of both forms with compound binding terms also enriched. Our results illustrate the need to consider both toxicokinetic and toxicodynamic mechanisms in the development of adverse outcome pathways for nanomaterials.
... Contamination of the soil environment with excessive Zn occurs from a variety of sources, including mining operations, transportation of Zn ore bodies, smelting and Zn plating industries (Lamb et al., 2009). In addition, high Zn levels have been found in soils below galvanised objects (Lock and Janssen, 2001). At metal(loid) contaminated sites, Zn is commonly found at proportionally high concentrations in comparison to other metal(loid)s, such as arsenic, cadmium, lead and copper. ...
... Studies on Zn toxicity to plants (McBride et al., 2009), invertebrates (Lock and Janssen, 2001) and microorganisms (Broos et al., 2007;Smolders et al., 2004) predominantly focus on total concentrations. Toxicity end points have been reported using dose-response studies in the laboratory (Warne et al., 2008b) and in short-term field studies (Heemsbergen et al., 2009; 2008a). ...
... The toxicity of these metals to the mite O. nitens when compared with their toxicity to the collembola, earthworm, enchytraeid, and isopod species commonly used in toxicity tests (Table 1) showed that the mite O. nitens is less sensitive to Cu and Zn but is within the same order of magnitude for Cd and Pb when compared with other soil invertebrates. When reproduction IC50 values for the least sensitive species were ranked to the 100th percentile and the IC50 values for other more sensitive species were relatively ranked with respect to that of the least sensitive species, for each metal, it became very clear that for Cd and Pb the mite O. nitens is within the 40th 305 [60] 566 [50] 267 [50] 476 [55] 158 [55] 11,400 [59] 320 [60] Enchytraeus crypticus to 60th percentile of toxicity for the least sensitive species, whereas for Cu and Zn, it is clearly the least sensitive species (Fig. 5). For hydrocarbon-and salt-contaminated soils from the boreal regions in Canada, the mite O. nitens was reported to have intermediate sensitivity when compared with standard and boreal earthworm (Eisenia fetida and Dendrodrilus rubidus) and collembolan (Folsomia candida, F. nivalis, and P. minuta) species [28]. ...
... The toxicity of these metals to the mite O. nitens when compared with their toxicity to the collembola, earthworm, enchytraeid, and isopod species commonly used in toxicity tests (Table 1) showed that the mite O. nitens is less sensitive to Cu and Zn but is within the same order of magnitude for Cd and Pb when compared with other soil invertebrates. When reproduction IC50 values for the least sensitive species were ranked to the 100th percentile and the IC50 values for other more sensitive species were relatively ranked with respect to that of the least sensitive species, for each metal, it became very clear that for Cd and Pb the mite O. nitens is within the 40th 305 [60] 566 [50] 267 [50] 476 [55] 158 [55] 11,400 [59] 320 [60] Enchytraeus crypticus to 60th percentile of toxicity for the least sensitive species, whereas for Cu and Zn, it is clearly the least sensitive species (Fig. 5). For hydrocarbon-and salt-contaminated soils from the boreal regions in Canada, the mite O. nitens was reported to have intermediate sensitivity when compared with standard and boreal earthworm (Eisenia fetida and Dendrodrilus rubidus) and collembolan (Folsomia candida, F. nivalis, and P. minuta) species [28]. ...
The oribatid mite Oppia nitens has been suggested as a test species for ecotoxicological assessment of contaminated boreal soils. Knowledge of the ecotoxicity of pollutants of different modes of action to this species is necessary to assess its relative sensitivity in comparison with other invertebrates. The toxicity of four metals and two organic chemicals to O. nitens was evaluated over a 28- or 35-d period. Mite survival, reproduction, and tissue accumulation were assessed at the end of the test. Reproduction was a more sensitive endpoint than survival for all of the compounds except geraniol. The reproduction median inhibitory concentration (IC50) values for Cu, Zn, Cd, and Pb were 2,896, 1,562, 137, and 1,678 mg/kg, respectively, whereas those for benzo[a]pyrene and geraniol were greater than 1,600 and 283 mg/kg. The median lethal concentration (LC50) values for Cu, Zn, Cd, and Pb were 3,311, 2,291, 603, and 6,761 mg/kg, respectively, whereas those for benzo[a]pyrene and geraniol were greater than 1,600 and 251 mg/kg. When effects on reproduction are compared with those of other soil invertebrates, O. nitens appears less sensitive to Cu and Zn but within the same order of magnitude of sensitivity as that for Cd and Pb. Despite its lower sensitivity to Cu and Zn, O. nitens is a member of a group underrepresented in ecotoxicological evaluations and should therefore be included in test battery for risk assessment of contaminated boreal and other northern soils.
... Normalisation relationships have generally been developed using linear regression analysis techniques including forward and backward stepwise regression (e.g. Smolders et al., 2004; Rooney et al., 2006; Broos et al., 2007; Warne et al., 2008a) or partial least squares (PLS) regression (e.g. Lock and Janssen, 2001). It is important that only soil physicochemical properties that are not significantly correlated to each other are used to develop normalisation equations. ...
... A number of studies have successfully developed normalisation relationships for plants, microbial processes and soil invertebrates. The main soil characteristics affecting the toxicity of inorganic contaminants appear to be pH, clay content, iron oxides, cation exchange capacity and organic matter content (e.g. Lock and Janssen, 2001; Smolders et al., 2003; Smolders et al., 2004; Rooney et al., 2006; Song et al. 2006; Broos et al., 2007; Warne et al., 2008a; Warne et al., 2008b). Normalisation equations can, in principle, be developed for any combination of contaminant, species, and toxicity endpoint. ...
... The suitability of the model was evaluated by assessing the homogeneity of the residuals (looking to the residuals versus fitted values plot), and their normality (by means of a normal QeQ-plot). Heavy metal content in soils was not included in the analysis, as they were expected not to influence the toxicity results, since their values were below those expected to affect survival ( Crommentuijn et al., 1993;Greenslade and Vaughan, 2003;Bongers et al., 2004;Lock and Janssen, 2001b) and reproduction in this species ( Lock and Janssen, 2001a, 2002a, 2002bFountain and Hopkin, 2005). ...
... However, this might be also be linked to the higher CEC of these soils, since in the set of soils used, CEC was correlated with organic carbon (r ¼ 0.688, p ¼ 0.04) but not with clay content. The lower toxicity of chemicals in soils with higher CEC is related to its influence on bioavailability ( Lock and Janssen, 2001a, 2001b, 2001dSimini et al., 2004). As an example, several authors have demonstrated CEC to be the best indicator to predict the bioavailability of metals to soil invertebrates ( Lock et al., 2000;Janssen, 2001a, 2001d;Römbke et al., 2006) and plants ( Rooney et al., 2006), as a result of the joint contribution of clay and organic matter, as well as other adsorption phases such as oxyhydroxides. ...
... They focused mostly on factors affecting the bioavailability of metals, e.g., soil moisture, pH, temperature, and content of organic matter or clay. These effects were extensively explored by, for example, Lock and Janssen12345 in Enchytraeus albidus, a close relative of the enchytraeid used in this study. Most such laboratory ecotoxicological studies are performed at low densities (usually 10 individuals), when population numbers increase quickly. ...
... At the two lowest densities, this interaction caused synergistic effects, indicating that ecotoxicological tests performed at optimal densities may underestimate real field effects in some circumstances. In fact, in most tests, the density of 10 individuals is used (e.g.,12345 ). In food-or space-limited environments , significant interactions, in that case most probably leading to compensation, are also possible. ...
Laboratory cultures of the potworm Enchytreaus doerjesi were exposed to zinc-contaminated soil at nominal concentrations 0, 75, 150, 300, or 600 mg Zn/kg dry weight for four weeks (one generation) at five different initial densities (5, 10, 20, 40, or 80 individuals per 20 g soil). The final culture numbers and the instantaneous population growth rate, r(i) were used as measures of culture response to both factors. In all treatments, the number of individuals increased during the experiment; thus, all the cultures exhibited positive r(i) values. The population growth rates decreased significantly with increasing Zn concentration and were also affected by the initial density. However, the latter effect was nonlinear and the initial density of 20 individuals resulted in the highest r(i) values throughout the whole range of Zn concentrations tested, while the lowest population growth rates were recorded for the highest initial density. Significant interaction between zinc toxicity and population size was
... However, although F. candida and E. crypticus have benefited from the same Zn concentration, E. crypticus was considerably more sensitive than F. candida, since at T5 (400 mg Zn kg −1 ) the first had its reproduction almost entirely inhibited, while F. candida only presented a similar reaction at T8 (2000 mg Zn kg −1 ). This difference in the sensitivity of F. candida and E. crypticus was also verified by other authors, who found E. crypticus to be more sensitive to a variety of metals and their combination (Gomes et al., 2022;Gonzalez-Alcaraz et al., 2019;Lock & Janssen, 2001;Renaud et al., 2020;Richter et al., 2015). Therefore, considering isolated metals and their combination, E. crypticus tends to be more sensitive than F. candida and may be a safer choice to evaluate such contaminants when performing an environmental assessment, as it is recommended to use the lowest EC or NOEC value of the tested species (European Commission, 2003). ...
Zinc (Zn) is an essential micronutrient for plants and an important component for maintaining soil quality. Commonly found in the soil due to anthropogenic activities, such as industrialization and application of organic waste as fertilizers, in high concentrations, Zn may induce soil toxicity, affecting important communities, such as edaphic fauna. Despite its high concentrations found in the environment, Zn bioavailability can be affected by the type of soil, organic matter content and pH. In this work, Zn had its toxicity evaluated in a natural tropical soil, sampled in São Paulo-Brazil, for two soil invertebrates (Folsomia candida, Enchytraeus crypticus) and two seeds (Lactuca sativa and Phaseolus vulgaris), through ecotoxicological tests. The invertebrate E. crypticus was exposed to Zn concentrations of 10.0 (T1); 100.0 (T2); 150.0 (T3); 200.0 (T4); 400.0 (T5) mg Zn kg⁻¹ of dry soil, while F. candida, L. sativa and P. vulgaris were exposed to Zn concentrations of 100.0; 200.0; 400.0; 800.0 (t6); 1600.0 (t7); and 2000.0 (t8) mg Zn kg⁻¹ of dry soil. The outcome evaluated were seed germination, for L. sativa and P. vulgaris, and reproduction, for F. candida and E. crypticus. The EC50 obtained for E. crypticus, F. candida, L. sativa, and P. vulgaris were 261.5, 1089.7, 898.5, and 954.5 mg Zn kg⁻¹ of dry soil, respectively, being E. crypticus the most sensitive organism, and only at the highest Zn’s concentrations the organisms’ reproduction and seeds’ germination showed a statistically significant inhibitory effect (p < 0.05). Therefore, this work’s results showed that Zn does not present significant toxicity for the tested soil organisms and seeds and that at 100 mg Zn kg⁻¹ of dry soil it can be beneficial to F. candida and E. crypticus’ reproduction and L. sativa’s germination. These results imply that the presence of Zn in low concentrations, both in soil and biofertilizers, such as sewage sludge, not only is not a concern, but it can even benefit certain crops and functions of edaphic organisms, which may contribute to the engagement of sustainable agricultural practices and the quest for food security.
... In organic matter, the presence of humic acid is also a very important parameter which shows a positive correlation with the bioavailability of these toxic metals to the plants (Lagier et al. 2000). The cation exchange capacity of the soil also strongly increases the bioavailability of heavy metals to the plants (Lock and Janssen 2001). High CEC means high exchangeable metals available for uptake of plants (Wong et al. 2002). ...
The review paper, summaries the results of heavy metal concentration reported by several authors in the soils of North Indian states viz. Punjab, Haryana, Rajasthan and Uttar Pradesh, and crop response towards different heavy metal exposure. The metals which are included in this review study are mainly Fe, Mn, Zn, Ni, Cu, Co, Mo, V, Cr, Pb, Cd,, and As. Different essential and non-essential metals in soil pose different toxic effects on the plants if present in exceeded concentrations. The level of toxicity varies from crop to crop and from metal to metal. Also the physico-chemical parameters of soils viz., pH, CEC, texture and organic matter influence the uptake of metals. Studies reveal that although the soils of North India are highly productive in nature, but the concentration of some heavy metals was found crossing the permissible limits at different locations. The cause of heavy metal contamination in different regions of North India is anthropogenic which includes the discharge of sewage sludge, fly ash, untreated industrial waste disposal on agricultural land, extensive use of agrochemicals, fertilizer, pesticides used in the agriculture processes. As the soils of Northern India are highly fertile and are in a threat of contamination, a detailed literature survey has been carried out to assess the contamination level and crop response to bring the attention of regulatory bodies and policy makers to take possible measures to prevent further contamination of the soils.
... This pattern has been found previously for certain chemicals, where E. crypticus was less sensitive than E. albidus, for instance to cadmium, carbendazim, phenanthrene (Castro-Ferreira et al., 2012) and atrazine (Gomes et al., 2019b). Results from studies in OECD artificial soil with E. albidus (Lock and Janssen, 2001) or Eisenia fetida (Spurgeon et al., 1997) showed Zn toxicity at slightly higher levels (reproduction EC50 of 267 and 308 mg Zn/kg for E. albidus and E. fetida, respectively). This is often the case when comparing toxicity results between soils with higher (OECD artificial soil) and lower organic matter contents (LUFA 2.2). ...
Zinc (Zn) is known to be relatively toxic to some soil-living invertebrates including the ecologically important enchytraeid worms. To reveal the molecular mechanisms of zinc toxicity we assessed the gene expression profile of Enchytraeus crypticus (Enchytraeidae), exposed to the reproduction effect concentrations EC10 and EC50, over 4 consecutive days, using a high-throughput microarray (species customized). Three main mechanisms of toxicity to Zn were observed: 1) Zn trafficking (upregulation of zinc transporters, a defence response to regulate the cellular zinc level), 2) oxidative stress (variety of defence mechanisms, triggered by Reactive Oxygen Species (ROS)), and 3) effects on the nervous system (possibly the primary lesion explaining the avoidance behaviour and also why enchytraeids are relatively susceptible to Zn). The adverse outcome at the organism level (reproduction EC50) could be predicted based on gene expression (male gonad development, oocyte maturation), with Zn at the EC50 affecting processes related to higher stress levels. The gene expression response was time-dependent and reflected the cascade of events taking place over-time. The 1 to 4 days of exposure design was a good strategy as it captured the time for sequence of events towards zinc adverse outcomes in E. crypticus.
... It has also been reported that, environmental and health effects of trace metals in soils depend on their mobility and bioavailability, which are a function of their partitioning with soils (Lee et al., 2005). It has been reported that soil pH and organic matter content are the main soil properties controlling the mobility and bioavailability of metals in soil (Bozkurt et Correlations between metal toxicity and pH, organic matter content, clay content and cation exchange capacity (CEC) were identified and where possible integrated into predictive models (Lock and Janssen, 2001;Spurgeon and Hopkin, 1996;Crommentuijn et al., 1997;Van Gestel et al., 1995). This research was undertaken to ascertain the roles of total trace metal, soil pH and organic matter on metal mobility and bioavailability in some urban dumpsite soils within Akwa Ibom State, Nigeria. ...
Roles of soil properties on metal mobility
... In the soil tests, the 10min ZINC-low-DI leachates show significant toxic effects for both eluate concentrations. In this context, it should also be noted that Lock and Janssen (2001) report that zinc toxicity to E. albidus is mainly depending on the pH and the cation exchange capacity of the soil. For TEDA-low-DI, only the pure eluate shows toxic effects at 10, 30 and 70 min while no toxic effects can be observed for the diluted eluate. ...
Leaching of polyurethane systems for waterproofing purposes of buildings was investigated in this study. As the curing step is the crucial point for potential impacts on the environment, leaching during this period was assessed by applying three different catalysts, in different amounts as well as two eluents. A modified and intensified version of the European horizontal dynamic surface leaching test was used. Complex assessment of all observed parameters was performed by using chemical as well as ecotoxicological tests. Inorganic and organic parameters were detected in a multi-method approach. The study was supplemented by an aquatic ecotoxicological assay on freshwater algae Desmodesmus subspicatus and a terrestrial assay with Enchytraeus albidus. While sum parameters like pH stayed constant over the test period, up to a maximum of 0.004 mmol/l Zn could be leached from one of the systems used in the intensified tank leaching test. Leaching of organic compounds reached a maximum (612 mmol/l) during the first leaching steps and decreased rapidly to a minimum. Ecotoxicological tests confirm the first leaching steps to be crucial as well as the dosage of the catalyst. Soil tests with E. albidus showed a realistic impact of the eluates on the environment.
... In many studies on earthworms, models for Zn toxicokinetics either could not be fitted at all or parameters could not be estimated properly (Ardestani et al., 2014). The main reason is that zinc, as an essential metal, is regulated efficiently by earthworms, even when they are exposed to concentrations exceeding those in their natural environment (Giska et al., 2014;Lock and Janssen, 2001a). In most cases, regardless of soil type (artificial/field), either initial rapid accumulation and then elimination as early as within the exposure period (Smith et al., 2010;Vijver et al., 2005) or steady state within 2-3 days (Peijnenburg et al., 1999) were observed. ...
The toxicokinetics of zinc in the earthworm Eisenia andrei was investigated following exposure for 21 days to ionic zinc (ZnCl 2) or zinc oxide nanoparticles (ZnO-NPs) in Lufa 2.2 soil, followed by 21 days elimination in clean soil. Two concentrations were tested for both ZnCl 2 (250 and 500 μg Zn g −1) and ZnO-NPs (500 and 1000 μg Zn g −1), corresponding to EC 25 and EC 50 for effects on reproduction. Based on the measured internal Zn concentrations in the earthworms over time of exposure, the kinetics parameters k a – assimilation rate constant (g soil g −1 body weight day −1) and k e – elimination rate constant (day −1) were estimated using a one-compartment model for either total Zn concentrations in the soil or porewater Zn concentrations. In the ZnCl 2 treatments, k a was higher for total Zn concentrations in soil, whereas in the ZnO-NP treatments, k a was higher for porewater Zn concentrations. The value of k e did not differ between the two Zn forms (ZnCl 2 vs ZnO-NPs) for either EC 50 or EC 25 when related to total Zn concentrations in soil, but for EC 50 , k e related to porewater Zn concentrations was significantly higher for ZnCl 2 than for ZnO-NPs. It is concluded that differences in kinetic parameters between treatments were connected with exposure concentrations rather than with the form of Zn. Zinc was efficiently regulated by the earthworms in all treatments: a 2-fold increase in exposure concentration resulted in a less than 2-fold increase in internal concentration, and after transfer to uncontaminated soil the internal Zn concentrations in the earthworms returned to ca 111 μg g −1 dw in all treatments.
... Some studies reported higher sorption of Hg from 4 to 5 pH values, indicating lower bioavalability (Kabata-Pendias, 2011;Kwon et al., 2017). Studies have shown that CEC values may be more explanatory in cases of contamination by metals than organic carbon and clay contents (Lock and Janssen, 2001b). This is because CEC is a measure of the amount of available sorption sites and is related to the organic carbon content, clay content as well as other adsorption phases such as iron and manganese oxyhydroxides in the soil, which can adsorb more easily to metals (Chapman et al., 2013). ...
Soil provides many ecosystem services that are essential to maintain its quality and healthy development of the flora, fauna and human well-being. Environmental mercury levels may harm the survival and diversity of the soil fauna. In this respect, efforts have been made to establish limit values of mercury (Hg) in soils to terrestrial fauna. Soil organisms such as earthworms and enchytraeids have intimate contact with trace metals in soil by their oral and dermal routes, reflecting the potentially adverse effects of this contaminant. The main goal of this study was to obtain Hg critical concentrations under normal and extreme conditions of moisture in tropical soils to Enchytraeus crypticus to order to assess if climate change may potentiate their acute and chronic toxicity effects. Tropical soils were sampled from of two Forest Conservation Units of the Rio de Janeiro State - Brazil, which has been contaminated by Hg atmospheric depositions. Worms were exposed to three moisture conditions, at 20%, 50% and 80% of water holding capacity, respectively, and in combination with different Hg (HgCl2) concentrations spiked in three types of tropical soil (two natural soils and one artificial soil). The tested concentrations ranged from 0 to 512mg Hg kg(-1) dry weight. Results indicate that the Hg toxicity is higher under increased conditions of moisture, significantly affecting survival and reproduction rate.
... This EC 50 value could be reached even in a dilution of 2.4% that was the EC 50 estimated for E. foetida in PSD. For Zn, EC 50 values of 375-900 and 186-336 mg/kg were reported for F. candida [39][40][41] and E. crypticus [42,43], respectively, and these values could be reached even in dilutions of 6.2% and 11.7%, that were the EC 50 values estimated for F. candida and E. crypticus, respectively, to the PSD compost. ...
Using organic wastes, as soil amendments, is an important alternative to landfilling with benefits to soil structure, water retention, soil nutrient and organic matter concentrations. However, this practice should be monitored for its environmental risk due to the frequent presence, of noxious substances to soil organisms. To evaluate the potential of eight organic wastes with different origins, as soil amendments, reproduction tests with four soil invertebrate species (Folsomia candida, Enchytraeus crypticus, Hypoaspis aculeifer, Eisenia fetida) were performed using gradients of soil–waste mixtures.
Results obtained demonstrated that contaminant concentrations required by current legislation might not be a protective measure for the soil ecosystem, as they do not properly translate the potential toxicity of wastes to soil invertebrates. Some wastes with contaminant loadings below thresholds showed higher toxicity than wastes with contaminants concentrations above legal limits. Also, test organism reproduction was differently sensitive to the selected wastes, which highlights the need to account for different organism sensitivities and routes of exposure when evaluating the toxicity of such complex mixtures. Finally this study shows that when combining chemical and ecotoxicological data, it is possible to postulate on potential sources of toxicity, contributing to better waste management practices and safer soil organic amendment products.
... Mineral sludge contained low concentrations of other metals Cr, Ni, Pb, Cu and Zn ranging from 8.2 to 51.8 mg/kg (Table S1). According to literature, concentrations of these elements in sludge are bellow reported EC10 for both organism E. crypticus and F. candida [45][46][47][48][49]. Even though the presence of other metals was very low (Table S1), we cannot exclude joint toxic effect of these metals in mineral sludge. ...
Sludge coming from remediation of groundwater contaminated by industry is usually managed as hazardous waste despite it might be considered for further processing as a source of nutrients. The ecotoxicity of phosphorus rich sludge contaminated with arsenic was evaluated after mixing with soil and cultivation with _Sinapis alba_, and supplementation into composting and vermicomposting processes. The _Enchytraeus crypticus_ and _Folsomia candida_ reproduction tests and the _Lactuca sativa_ root growth test were used. Invertebrate bioassays reacted sensitively to arsenic presence in soil-sludge mixtures. The root elongation of _L. sativa_ was not sensitive and showed variable results. In general, the relationship between invertebrate tests results and arsenic mobile concentration was indicated in majority endpoints. Nevertheless, significant portion of the results still cannot be satisfactorily explained by As chemistry data. Composted and vermicomposted sludge mixtures showed surprisingly high toxicity on all three tested organisms despite the decrease in arsenic mobility, probably due to toxic metabolites of bacteria and earthworms produced during these processes. The results from the study indicated the inability of chemical methods to predict the effects of complex mixtures on living organisms with respect to ecotoxicity bioassays.
... The aging factor and other soil properties are the main factors affecting the bioavailability of heavy metals (Ahmad and Goni 2010; Smolders et al. 2009). The sensitivity of heavy metals in soil is greatly affected by soil CEC and pH (Lock and Janssen 2001). The pedotransfer function assessment is now commonly used to understand heavy metal mobility and availability in soil environment. ...
Heavy metal contamination is a globally recognized environmental issue, threatening human life very seriously. Increasing population and high demand for food resulted in release of various contaminants into environment that finally contaminate the food chain. Edible plants are the major source of diet, and their contamination with toxic metals may result in catastrophic health hazards. Heavy metals affect the human health directly and/or indirectly; one of the indirect effects is the change in plant nutritional values. Previously, a number of review papers have been published on different aspects of heavy metal contamination. However, no related information is available about the effects of heavy metals on the nutritional status of food plants. This review paper is focused upon heavy metal sources, accumulation, transfer, health risk, and effects on protein, amino acids, carbohydrates, fats, and vitamins in plants. The literature about heavy metals in food plants shows that both leafy and nonleafy vegetables are good accumulators of heavy metals. In nonleafy vegetables, the bioaccumulation pattern was leaf > root ≈ stem > tuber. Heavy metals have strong influence on nutritional values; therefore, plants grown on metal-contaminated soil were nutrient deficient and consumption of such vegetables may lead to nutritional deficiency in the population particularly living in developing countries which are already facing the malnutrition problems.
... The first two workshops both supported a role for the artificial soil acute toxicity test, in screening chemical toxicity. This included not only classical toxicity studies Callahan et al. 1994;Edwards & Bohlen 1992;Lock et al. 2002;Robidoux et al. 1999;Spurgeon et al. 1994), but also field soil assessment (Bierkens et al. 1998;Charrois et al. 2001;Dorn et al. 1998;Saterbak et al. 1999;Spurgeon & Hopkin 1995), remediation evaluation (Ducrocq et al. 1999;Jarvis et al. 1998;Saterbak et al. 2000;Sayles et al. 1999;Van Gestel et al. 2002) and evaluations of bioavailability (Amorim et al 2002;Lock et al. 2002;Lock & Janssen 2001b;Lock et al. 2000;Spurgeon & Hopkin 1996c). ...
The inception, ring-testing and standardisation of the acute earthworm toxicity test (OECD 1984), has been at catalyst for the emergence of earthworms as one of the key organisms in (environmental) toxicology. In recognition of this role, there have now been three International Workshops on Earthworm Ecotoxicology (Sheffield in 1991, Amsterdam in 1997 and Aarhus, in 2001). At each workshop delegates met to outline recent work and identify future priorities. At the end of each workshop, recommendations were drawn up both to act as a summary of current knowledge and as initiators for future research. in this paper we briefly review progress in respect of these recommendations. Overall, advances have been made in many areas. Test procedures for laboratory and field toxicity tests have been improved and diversified, thus allowing specific studies not covered by the original OECD (1984) procedure. Further, there is now improved understanding of factors that can modify the effects of chemicals in dynamic ecosystems and also of the mechanistic basis of toxicosis (although many uncertainties still remain in these areas). One notable area where progress has been slower is development of a linked earthworm ecotoxicology community. In particular recommendations to develop comprehensive databases have yet to be implemented.
... Moreover, a high organic matter content in soil resulted in increased organic matter in the bound fractions (F3 and F4) over time (Table 2). These results show that the metal fraction in soil was related to changes in the organic matter content due to microbial activity (Lock and Janssen 2001). Investigations relative to these questions should complement the present approach for a full understanding of the multifaceted issue of bioavailability in soil systems. ...
We investigated the effect of Pb uptake by Pinus densiflora and the Pb fraction in forest soil. We also investigated the change in soil physicochemical characteristics, microbial activity, and root exudates of Pinus densiflora in Pb-contami-nated soils. Three-year-old pine seedlings were exposed to 500 mg/kg Pb for 12 months. The metal fractions were mea-sured using sequential extraction procedures. Additionally, factors that affect solubility (three soil enzyme activities and amino acids of root exudate compounds) were also determined. The results showed that Pb contamination significantly decreased enzyme activities due to soil characteristics. In addition, organic matter, nitrate content, and Pb concentra-tion were time dependent. The results indicate that changes in the Pb fraction affected Pb uptake by pine trees due to an increase in the exchangeable Pb fraction. The concentrations of organic acids were higher in Pb-spiked soil than those in control soil. Higher rhizosphere concentrations of oxalic acid resulted in increased Pb uptake from the soil. These results suggest that pine trees can change soil properties using root exudates due to differences in the metal fraction.
... Regarding the influence of texture, it is widely accepted that fine-textured soils generally show lower toxicity to heavy metals (Lock and Janssen 2001a) and organic pollutants (Simini et al. 2004) due to a lower bioavailability. However, in our study, the toxicity for reproduction, measured as the number of juveniles, was higher in soils with extreme textures (high percentage of coarse sand or clay content). ...
... In addition, Cornelis et al. [33], found a strong relationship between soil organic carbon content and partitioning dissociation constant values for Ag nanoparticles. Although previous research to date has not reported relationships between partitioning of Ag and soil pH, this property has been found to have a significant effect with other metals [13,[34][35][36]. The toxicity relationships that have been generated for Ag in the present study can assist in future terrestrial risk assessments of Ag and will advance our understanding of the environmental behavior of Ag in soils and how that is associated with its toxicity. ...
Silver (Ag) is being increasingly used in a range of consumer products, predominately as an antimicrobial agent, leading to a higher likelihood of its release into the environment. This study investigated the toxicity of Ag to the soil nitrification process in a European and Australian soils in both leached and unleached conditions. Overall, leaching of the soils was found to have a minimal effect on the final toxicity data with average leaching factors of approximately 1. Across the soils the toxicity was found to vary by several orders of magnitude with concentrations of Ag causing a 50% reduction in nitrification relative to the controls (EC50) ranging from 0.43 to > 640 mg Ag/kg. Interestingly, the dose response relationships in most of the soils showed significant stimulation in nitrification at low Ag concentrations (i.e. hormesis), which in some cases produced responses up to double that observed in the controls. Soil pH and organic carbon (OC) were the properties found to have the greatest influence on the variations in toxicity thresholds across the soils and significant relationships were developed that accounted for approximately 90% of the variability in the data. The toxicity relationships developed from this study will assist in future assessment of potential Ag risks and enable the site-specific prediction of Ag toxicity. Environ Toxicol Chem © 2014 SETAC.
... Mobility, bioavailability and therefore the potential toxicity or deficiency of most elements for plants and microorganisms in terrestrial system are controlled largely by soil properties (Sheppard and Evenden 1988). The main soil properties affecting As availability are as follows: Fe oxides, pH, calcium carbonate, clay content, cation-exchange capacity and organic matter content (Lock and Janssen 2001;Smolders et al. 2003Smolders et al. , 2004Rooney et al. 2006;Song et al. 2006). ...
Purpose
The present work evaluates the influence of different soil properties and constituents on As solubility in laboratory-contaminated soils, with the aim of assessing the toxicity of this element from the use of bioassays to evaluate the soil leachate toxicity and thereby propose soil guideline values for studies of environmental risk assessment in soil contamination.
Materials and methods
Seven soils with contrasting properties were artificially contaminated in laboratory with increasing concentrations of As. Samples were incubated for 4 weeks, and afterwards, soil solution (1:1) was obtained after shaking for 24 h. The soil leachate toxicity was assessed with two commonly used bioassays (seed germination test with Lactuca sativa and Microtox ® test with Vibrio fischeri).
Results and discussion
The relationship between soluble As and soil properties indicated that iron oxides and organic matter content were the variables most closely related to the reduction of the As solubility, while pH and CaCO3 increased As solubility in the soil solutions. Toxicity bioassays showed significant differences between soils depending on their properties, with a reduction of the toxicity in the iron-rich soil (no observed effect concentration (NOEC) = 150 mg kg−1) and a significant increase in the highly carbonate samples (NOEC between 15 and 25 mg kg−1).
Conclusions
Soil guideline values for regulatory purposes usually set a single value for large areas (regions or countries) which can produce over- or underestimation of efforts in soil remediation actions. These values should consider different levels according to the main soil properties controlling arsenic mobility and the soil leachate toxicity.
... This means that the relation of cadmium sorption and C org content does not explain the variability between soils. This might be expected because not only organic matter content but predominantly cation exchange capacity and pH are known to be important for the sorption of metals in soils (van Gestel 1992;Lock and Janssen 2001b;Spurgeon and Hopkin 1996). However, the effect of pH is not responsible in this case, because of the same pH values of all soils (6.0 ± 0.5). ...
In the EU Waste Ring test 2006/2007 a very high number of reference tests were performed for three standard (Algae, Daphnia and Luminescent bacteria) as well as various additional (Lemna, Brachyonus, Ceriodaphnia, and Pseudomonas) test systems. These results were required by the respective test guidelines to prove the sensitivity of the test organisms.
In addition, tests with two reference substances provided results confirming the validity of the umu tests performed. Besides
the required reference substances, in some tests additional chemicals were tested. The number of the required reference tests,
mainly potassium dichromate in the standard tests, was so high that these results could be used for the re-evaluation of the
data ranges listed in the test guidelines. The range given in the current Algae test guideline, based on old ring test data,
should be changed and so a new range is proposed here. In the additional tests, the number of data sets provided, often with
different reference substances, was much lower. Since potassium dichromate did not cause problems in the various tests, it
is recommended that this substance be used as the standard reference substance in aquatic tests.
... This means that the relation of cadmium sorption and C org content does not explain the variability between soils. This might be expected because not only organic matter content but predominantly cation exchange capacity and pH are known to be important for the sorption of metals in soils (van Gestel 1992;Lock and Janssen 2001b;Spurgeon and Hopkin 1996). However, the effect of pH is not responsible in this case, because of the same pH values of all soils (6.0 ± 0.5). ...
The statistical evaluation of the ring test data (only standard test battery) was performed in a step-wise process. First,
the individual test results (EC/LC50 values) were recalculated (using probit analysis and the ToxRat program). Secondly, they had to fulfil several acceptance
criteria. Data sets which passed these acceptance criteria were evaluated in two different ways in parallel: according to
the approach usually used for the validation of chemical and physicochemical methods in environmental analysis (ISO 5725-2
(2002)) and according to the warning limit approach following Environment Canada (2005). However, for the evaluation of the
results from ecotoxicological tests, the ISO approach had to be modified. Assuming that EC/LC50 values are log-normally distributed, the log-transformed EC/LC50 values were used instead of the original EC/LC50 values, to calculate means and standard deviations. Hence the re-transformed total means are not arithmetic but geometric
means. Since the ecotoxicological test procedures in question are tedious and elaborate compared with trace analytical investigations,
replicate determinations within a given laboratory and within short intervals of time were impossible. Thus, repeatability
and reproducibility were evaluated using the results of the different laboratories together with the confidence intervals
of the results, which were each calculated by application of the same algorithm. In addition, the results of the individual
tests were used to calculate warning limits according to Environment Canada (2005). The test results that were identified
as statistical outliers (ISO approach) or those outside the warning limits (Environment Canada) were excluded from the calculation
of the final geometrical mean EC/LC50. As a measure of robustness, the ratio between reproducibility and repeatability standard deviation, the standard deviations
calculated according to the warning limit approach and the factor between minimum and maximum EC/LC50 value are presented. Finally, recommendations to improve the statistical evaluation of data from ecotoxicological ring tests
are given.
... Predictions need to be compared to actual toxicity tests (e.g., phytotoxicity), and to field observations as all pools of metals in soil do not have equal bioavailability. Initial work by Lock and Janssen (2001b) relating Zn toxicity to an earthworm, potworm, and springtail to pH and CEC of artificial and natural soils is promising in this regard. ...
Ecological risk assessment (ERA) of inorganic metals and metalloids (metals) must be specific to these substances and cannot be generic because most metals are naturally occurring, some are essential, speciation affects bioavailability, and bioavailability is determined by both external environmental conditions and organism physiological/biological characteristics. Key information required for ERA of metals includes: emissions, pathways, and movements in the environment (Do metals accu-mulate in biota above background concentrations?); the relationship between inter-nal dose and/or external concentration (Are these metals bioreactive?); and the incidence and severity of any effects (Are bioreactive metals likely to result in adverse or, in the case of essential metals, beneficial effects?) — ground-truthed in contami-nated areas by field observations. Specific requirements for metals ERA are delineated for each ERA component (Hazard Identification, Exposure Analysis, Effects Analysis, Risk Characterization), updating Chapman and Wang (2000). In addition, key spe-cific information required for ERA is delineated by major information category (conceptual diagrams, bioavailability, predicted environmental concentration [PEC], predicted no effect concentration [PNEC], tolerance, application [uncertainty] fac-tors, risk characterization) relative to three different tiered, iterative levels of ERA: Problem Formulation, Screening Level ERA (SLERA), and Detailed Level ERA (DLERA). Although data gaps remain, a great deal of progress has been made in the last three years, forming the basis for substantial improvements to ERA for metals.
... At present, evidence for porewater-related uptake of metals is present only for a limited number of plant species and for microorganisms. Other soil-dwelling organisms such as invertebrates are probably exposed via a combination of uptake routes, such as porewater, food, and direct ingestion of soil (Lock and Janssen 2001). Uptake by soil organisms and bioavailability from the soil is not, or is only poorly, related to pH for zinc. ...
A risk assessment on zinc and zinc compounds was carried out within the framework of Council Regulation 793/93/EEC on Existing Chemicals. This risk assessment basically followed the European Union (EU) technical guidance documents (TGDs). These TGDs are built on the current knowledge on quantitative risk assessments, mainly for organic chemicals. This article describes the tailor-made approach for the zinc risk assessment. This work lasted almost a decade and involved the contributions of all EU member states and industry, who discussed the risk assessment during technical meetings. The risk assessment is initially based on scientific findings but is interrelated with pragmatic considerations. It follows a comprehensive approach, covering both environmental and human health. In the environmental part, new methodologies were developed to deal with the natural background of zinc, essentiality, speciation, and the use of species sensitivity distributions. The major results and the process of drawing conclusions of the risk assessment are outlined: potential environmental risks of zinc and zinc compounds may occur at local and regional scales in surfacewater, sediment, and soil. No potential health risks were identified for consumers and man indirectly exposed via the environment. For workers, potential health risks were identified only for zinc oxide and zinc chloride.
... This means that the relation of cadmium sorption and C org content does not explain the variability between soils. This might be expected because not only organic matter content but predominantly cation exchange capacity and pH are known to be important for the sorption of metals in soils (van Gestel 1992;Lock and Janssen 2001b;Spurgeon and Hopkin 1996). However, the effect of pH is not responsible in this case, because of the same pH values of all soils (6.0 ± 0.5). ...
Earthworms are considered an important part of the soil community, so they represent soil organisms in the test set for the
ecotoxicological characterization of wastes. In keeping with the ISO standard guideline 11268-1, the acute earthworm test
was performed with three waste types: INC, SOI, and WOO. A total of 44 tests out of the 52 tests conducted were classified
as acceptable. Methodologically, almost no problems occurred, but further guidelines on determining the moisture of the test
substrate mixtures are needed. After statistical evaluation, only one other test result was rejected. The min-max factors
(2–5) between individual LC50 values and the CVs (20–31%) were low, showing that the acute earthworm test is a robust method. Toxicity differed considerably
between the three waste types, as seen in the final LC50 values: INC = 46.3%, SOI ³ 50%, WOO = 21.0%. These results are in agreement with the few data known from the literature.
The sensitivity of the earthworm acute test was low compared to other plant and invertebrate tests with solid wastes. Therefore,
it is recommended that a more sensitive alternative be found: either an earthworm test with a chronic endpoint such as reproduction,
or another invertebrate species (e.g. a collembolan) should replace this test. In addition, an alternative for the currently
used reference substance chloroacetemide (boric acid) should be selected.
Keywords
Eisenia fetida/andrei
-Acute test-Ring test-Waste-Ash-Wood-PAH
... Lock and Janssen [9] showed that all literature toxicity data for the springtail F. candida, exposed to soils freshly spiked with zinc, reported 28 d EC50s of less than 1000 mg Zn kg -1 dry wt. Based on this type of toxicity data, the deleterious effect of zinc contamination on springtail communities was expected to be much higher. ...
Springtails were sampled monthly with pitfall traps in the ancient Pb-Zn mining area of Plombières for one year. Based on the total soil concentrations of lead, zinc, cadmium and copper, it was expected that zinc would probably have the most adverse effects on the populations. Activity and species richness of springtails were negatively related to the total zinc concentration in the soil, the water-soluble and the calcium chloride extracted zinc fractions. However, these relationships were only significant for the calcium chloride extracted fraction. The latter fraction might therefore be a good indicator of bioavailable zinc for springtails. Despite the high total soil concentrations of zinc, springtails were still quite abundant at all sampling sites. This is probably caused by the low bioavailability of zinc to the springtails in the soils of the study sites.
... The bioavailability of zinc in soil varies predictably with soil-specific factors, such as pH (Spurgeon and Hopkin, 1996; Van Beelen and Fleuren-Kemilä, 1997; Smit and van Gestel, 1998; Lock et al., 2000), organic matter content (Spurgeon and Hopkin, 1996; Van Beelen and FleurenKemilä, 1997; Smit and van Gestel, 1998), and/or cationic exchange capacity (Smit and van Gestel, 1998; Lock et al., 2000 ), and this is reflected in models that are currently suggested for assessing the toxicity of zinc to terrestrial organisms exposed in single-species test systems (see e.g., Lock and Janssen, 2001a). However, recent studies show that aged zinc-contaminated soils are less toxic than predicted from these models (Smit and van Gestel, 1998; Lock and Janssen, 2001b ), and that zinc toxicity to terrestrial organisms may be affected by the presence of other metals in the soil or soil solution (Van Gestel and Hensbergen, 1997; Sharma et al., 1999) and previous exposure to zinc or other metals (McLaughlin and Smolders, 2001; Salminen et al., 2001). Thus, even when considering a single species in a controlled laboratory setting, assessing metal bioavailability and toxicity is a complex issue. ...
The effect of zinc on soil nitrification and composition of the microbial community in soil was investigated using a full factorial experiment with five zinc concentrations and four levels of biological complexity (microbes only, microbes and earthworms (Eisenia fetida), microbes and Italian ryegrass (Lolium multiflorum var. Macho), and microbes, ryegrass and earthworms). After 6 weeks of exposure, the activity of soil nitrifying bacteria was measured and the microbial community structure was characterized by phospholipid fatty acid (PLFA) analysis. Soil nitrification and several PLFA markers were significantly influenced by either zinc addition and/or the presence of earthworms or ryegrass, and one of the most pronounced changes was the increase of fungi and decrease of bacteria with increasing concentrations of zinc. Of particular interest, however, was the potential interaction between the presence of plants and/or earthworms and the effect of zinc, which the factorial study design allowed us to explore. Such an effect was observed in two cases: Earthworms reduced the positive effect of zinc on the fungal biomass (ANOVA, p = 0.03), and the effect of earthworms on the soil nitrification activity depended on zinc concentration (ANOVA, p < 0.05). The effect of earthworm presence was not very large, but it does show that multispecies tests might give information about metal toxicity or bioavailability that cannot be predicted from single-species tests.
This review article focuses on the potential of biopolymer-based nanocomposites incorporating nanoparticles, graphene oxide (GO), carbon nanotubes (CNTs), and nanoclays in adsorption and membrane filtration processes for water treatment. The aim is to explore the effectiveness of these innovative materials in addressing water scarcity and contamination issues. The review highlights the exceptional adsorption capacities and improved membrane performance offered by chitosan, GO, and CNTs, which make them effective in removing heavy metals, organic pollutants, and emerging contaminants from water. It also emphasizes the high surface area and ion exchange capacity of nanoclays, enabling the removal of heavy metals, organic contaminants, and dyes. Integrating magnetic (Fe2O4) adsorbents and membrane filtration technologies is highlighted to enhance adsorption and separation efficiency. The limitations and challenges associated are also discussed. The review concludes by emphasizing the importance of collaboration with industry stakeholders in advancing biopolymer-based nanocomposites for sustainable and comprehensive water treatment solutions.
Research has shown that the fractions in which heavy metals exist in the soil are the prime determinant of their availability and uptake in plants. Through comprehensive studies that have been conducted on heavy metal fractions in soils, there is a dearth of information on the fractions of heavy metals of study locations. Therefore, this research investigated the concentrations of Pb, Cd, Cr, and Ni in selected dumpsites soils located at Osogbo, Ife, Ilesha, and Ido-Osun towns of Osun State and the fractions in which the metals exist in the soils. Each dumpsite was sampled in a completely randomized block design with 3 replicates and soil samples collected at a depth of 0-30cm. The soils were subjected to routine analysis and analyzed for total Pb, Cd, Cr, and Ni concentrations. The soil's heavy metal fractions were also analyzed by sequential extraction procedure (SEP), and their concentrations were read using an atomic absorption spectrometer (AAS). The results revealed that the soil pH ranged from 6.73-8.23, Organic Carbon ranged from 22.99-43.05 (g/kg), the soils are sandy loam in texture except for Ife dumpsite that is sandy clay loam. The heavy metal concentrations (mg/kg) of the dumpsite soils ranged from 95.5-177.34 for Pb, 1.18-15.16 for Cd, 24.17-55.14 for Cr, and 37.10-42.39 for Ni. There were significant differences (p<0.05) in concentrations of Pb, Cd and Cr among the dumpsites except for N. Pb and Cd concentrations in the soil were above the FAO/WHO permissible levels. However, Cr and Ni were below the levels. Most considerable pro-portions of the heavy metals were found in the residual fractions of the soil followed by the reducible fraction while exchangeable fractions had the least concentrations of the metals. The order of concentrations of most of the heavy metals in the soil fractions was: residual > reducible > oxidizable > exchangeable fraction.
The oribatid soil mite Oppia nitens C.L. Koch, 1836, is a model microarthropod in soil ecotoxicity testing. This species has a significant role in supporting soil functions and as a suitable indicator of soil contamination. Despite its significance to the environment and to ecotoxicology, however, very little is known of its biology, ecology, and sub‐organismal responses to contaminants in the soil. In this review, we give detailed and critical insight into the biology and ecology of O. nitens in relation to traits that are crucial to its adaptive responses to contaminants in soil. We used a species sensitivity distribution model to rank the species sensitivity to heavy metals (cadmium and zinc) and neonicotinoids (imidacloprid and thiacloprid) compared to other standardized soil invertebrates. Although the International Organization of Standardization (ISO) and Environment and Climate Change Canada (ECCC) are currently standardizing a protocol for the use of O. nitens in soil toxicity testing, we believe that O. nitens is limited as a model soil invertebrate until its molecular pathways associated with its response to contaminants are better understood. These molecular pathways can only be elucidated with information from the mites’ genome or transcriptome, which is currently lacking. Despite this limitation, we propose a possible molecular pathway to metal tolerance and a putative adverse outcome pathway (AOP) to heavy metal toxicity in O. nitens. This article is protected by copyright. All rights reserved.
Increasing concentrations of metals in soil have posed a serious threat to the soil environment. The control and evaluation of soil metal hazards demand the establishment of soil ecological criteria, which is mainly based on the obtainment of toxicity thresholds. As the most typical representative of soil-dwelling springtails, Folsomia candida performs numerous essential ecological functions in soil and has been extensively used to investigate metal toxicity effects and thresholds. This review outlined the current state of knowledge on the metal toxicity thresholds to Folsomia candida, including (1) toxicity thresholds of soil metals for the different endpoints, (2) the influence factors of metal toxicity thresholds including the test conditions, the chemical forms of metal, the soil physicochemical properties, aging time and leaching, (3) the bioavailable fractions predicting metal toxicity thresholds, (4) the internal threshold of metals. To conclude, several recommendations for future research are given to obtain the more reliable toxicity thresholds and further supplement the toxicity data of metals to Folsomia candida.
Organisms in soil are often exposed to different mixtures of contaminants. These contaminants may interact with each other and, consequently, may have a different effect on organisms than each of them alone. We wanted to investigate possible effects of ZnO mixtures in bulk and nano form and fungicide propiconazole (PCZ) on biochemical parameters and reproduction in Enchytreus albidus. These compounds were applied separately and in binary mixture. In the single exposure experiment the EC50 values for the number of juveniles were calculated: nano ZnO (641.21 ± 88.82 mg kg−1), bulk ZnO (445.78 ± 148.4 mg kg−1) and PCZ (3.63 ± 1.68 mg kg-1), respectively. These concentrations were subsequently used in the binary exposure experiment. Calculated combination indices (CI), that allow quantitative determination of chemical interactions at different concentration and effect level, indicated additive or antagonistic interactions (CI ≥ 1) of applied mixture ratios. The only ratio that showed synergistic interaction (CI < 1) was 75% EC50 nZnO/25% EC50 PCZ. Both ZnO forms caused acetylcholinesterase (AChE) activity increase of up to 40% of control level, as well as increased catalase (CAT) and glutathione S-transferase (GST) activities and malondialdehyde (MDA) level. PCZ did not affect AChE and CAT activities, yet it increased GST activity and MDA level. Induced levels of measured biomarkers indicate an oxidative stress after binary exposure, as well. These effects were not enhanced after binary exposure but reflected the effects on biomarkers that corresponding concentrations of these compounds generated in a single exposure experiment.
Les résultats obtenus au cours des travaux de thèse traitent dans une première partie de l’applicabilité et des limitations des bio-essais à l’étude des MF (problématiques telles que l’hydratation des échantillons, l’apport de nourriture, l’extraction des organismes de matrices complexes,…). D’autre part, la réponse des critères d’effet étudiés pour chacun des deux organismes (i.e. mortalité, croissance, et reproduction pour C. elegans ainsi que mortalité et reproduction pour H. aculeifer) a été renseignée après exposition à différentes substances chimiques préconisées en tant que substances de référence. La deuxième partie présente la sensibilité des organismes étudiés par rapport à des éléments contaminant (i.e. ETM) pouvant potentiellement être apportés au sol lors de l’épandage de MF. La dernière partie des résultats concerne l’évaluation de différentes MF par approche directe et indirecte, en utilisant les critères d’effet définis pour les deux organismes modèles. La discussion des travaux de thèse est axée en premier lieu sur la comparaison de la sensibilité des critères d’effet suivis chez les deux organismes modèles pour les différentes substances chimiques étudiées. Dans un second temps, la pertinence d’intégrer les organismes modèles C. elegans et H. aculeifer dans des batteries de bio-essais est discutée, cela afin de proposer, à terme, une stratégie expérimentale permettant une caractérisation a priori des dangers pour l’environnement liés à l’utilisation agricole des MF
The influence of soil properties on toxicity threshold values for Pb toward soil microbial processes is poorly recognized. The impact of leaching on the Pb threshold has not been assessed systematically. Lead toxicity was screened in 17 Chinese soils using a substrate-induced nitrification (SIN) assay under both leached and unleached conditions. The effective concentration of added Pb causing 50% inhibition (EC50) ranged from 185 to > 2515 mg/kg soil for leached soil and 130 to > 2490 mg/kg soil for unleached soil. These results represented > 13- and > 19-fold variations among leached and unleached soils, respectively. Leaching significantly reduced Pb toxicity for 70% of both alkaline and acidic soils tested, with an average leaching factor of 3.0. Soil pH and CEC were the two most useful predictors of Pb toxicity in soils, explaining over 90% of variance in the unleached EC50 value. The relationships established in the present study predicted Pb toxicity within a factor of two of measured values. These relationships between Pb toxicity and soil properties could be used to establish site-specific guidance on Pb toxicity thresholds.
This study compared four health risk assessment models and one analytical contaminant transport model used in Finland. In addition, experiments were done on the program linking spatial data to risk assessment. The health risk assessment models evaluated were: RISC-HUMAN developed in the Netherlands, SOILIRISK developed in Finland, the Swedish SNV's program and RISC on behalf of Bp Oil International Ltd. Only the SNV's program can be freely downloaded from the Internet. Golder Associates Ltd has developed a chargeable contaminant transport model called ConSim and a fully functional freeware version entitled Spatial Analysis and Decision Assistance program SADA is available for download on their this web site. At the beginning of the study a review was done on environmental management regulations and guidelines for soil pollution and cleaning needs assessment, ecological risk assessment and contaminant processes and transport modelling. For evaluation of the content of the selected models, the chemical data, landuse scenarios, soil and exposure parameters and result data were described in detail. To determine the differences and similarities of results from risk assessment and contaminant transport models, they were used with input data obtained from three case study test sites. The first test site describes contaminated service station properties, another test site is contaminated with chlorinated organic substances in a landfill area and the final site deals with PAHs and metals at an industrial estate. The input data of the case study test sites was based on real field sites. During the project separate risk assessments were compiled for the real field sites. For the comparison of risk assessment programs, the data of the real field sites was changed somewhat to be more suitable for a comparison of the programs. Risk assessment included evaluation of the uncertainty of the results and outcome of the most significant variables affecting the determination. This study also gathered together information presented in various publications on the different variables influencing the outcome of the risk assessment. New results on key factors effecting the concentration of groundwater were evaluated by sensitivity analysis. The comparison of risk assessment and transport model with data from the case study began by examining interphase mass transfer of contaminants. Results of the case study test site show that with homogeneous chemical properties, interphase mass transfer is similar to the various risk assessment models. The next examination were on migration of contaminants into the outside air, indoor air, groundwater and plants. In summary, the calculated indoor and outdoor concentrations differed less than one order of magnitude, which can be regarded as reasonable. The biggest differences were in the calculation of groundwater concentration. Significantly lower concentrations were obtained by using RISC than the other risk assessment model containing a groundwater migration option or the ConSim model which is designed for the calculation of groundwater transport. SNV's model predicted the highest concentration that deviated from concentrations obtained by RISC, by at most two orders of magnitude, and concentrations calculated by SOILIRISK by less than one order of magnitude. Risk assessment models differ in the final results, making it difficult to compare the results of the models. Most models separately calculate excess risk of cancer for carcinogens and then for non-carcinogenic toxicants a hazard quotient, which is obtained by comparing an estimated exposure to the acceptable dose (RfD, Reference Dose). RISC-HUMAN, however, calculates for all toxicants the hazard quotient. When calculating of the hazard quotient for carcinogens, a value of 1×10-4 is used for the excess life-long risk of cancer. With RISC-HUMAN, it is possible to compare the concentration of contaminant in the air to acceptable concentration. RISC, SNV's model, and RISC-HUMAN calculate a cumulative hazard index, which does not take into account the adverse effect mechanism of contaminant and effects of the target organ, but rather evaluate together all levels of risk. SOILIRISK sets out the main results of the contaminants in concentrations of the percentages calculated in acceptable maximum values. These results also present similarly active contaminants as well as the overall summary, the sum of the different routes of exposure effect. Cancer risk evaluates the effect of the most carcinogenic compounds as a whole. A sensivity assessment was used to evaluate the effect of various parameters on the results of risk assessment models. The contaminant's properties partly effect the assessment of parameter significance. In general, the modelling transport pathway to the receptor in risk assessment models substantially affected the organic carbon content, porosity, hydraulic conductivity and groundwater recharge. The most importance in case of modelling indoor air concentrations is the ventilation rate and pressure difference. The results of the risk assessment model comparison do not in itself give information on how "correct" one of the models calculates. The underlying assumptions and calculation formulas of models can be studied to evaluate how the model is able to take into account, for example soil conditions, building characteristics and other exposure factors under the considered site. The decision to use a particular risk assessment model should always be decided on a case-bycase basis. Selection can be based on results of comparison of risk assessment models described in this report. Risk assessment is usually initiated with relatively simple models, which may be the SNV-model and then if necessary move to more demanding models using more input information and resources.
A suite of organisms from different taxonomical and ecological positions are needed to assess environmentally relevant soil toxicity. We herein present a new bioassay based on Dictyostelium that is aimed at integrating slime moulds into such a testing framework. Toxicity tests on elutriates and the solid phase developmental cycle (DDDC) assay were successfully applied to a soil spiked with a mixture of Zn, Cd and diesel fuel freshly prepared (RC) and after 2 yr ageing (AC). The elutriates of both soils provoked toxic effects but toxicity was markedly lower in the aged soil. In the DDDC assay both soils affected amoeba viability and aggregation, with fewer multicellular units, smaller fruiting bodies and, overall, inhibition of fruiting body formation. This assay is quick and requires small amounts of test soil, which might facilitate its incorporation into a multispecies multiple-endpoint toxicity bioassay battery suitable for environmental risk assessment in soils. This article is protected by copyright. All rights reserved.
Variation in soil properties may cause substantial differences in metal bioavailability and toxicity to soil organisms. In this study, lead bioavailability and toxicity to Enchytraeus crypticus was assessed after 21 days exposure to soils from different landscapes of a shooting range containing 47–2398 mg Pb/kg dry weight (dw). Soils had different pHCaCl2 (3.2–6.8) and organic matter contents (3.8–13% OM), therefore artificial soils with different pH and OM contents and two natural reference soils were included as controls. Effects on survival and reproduction and the uptake of Pb in E. crypticus were related to soil properties and total, water- and CaCl2-extractable and porewater Pb concentrations in the soils. Forest soils with pHCaCl2 < 3.5 and total Pb concentrations ≥2153 mg/kg dw had the highest bioavailability and toxicity of Pb to E. crypticus. At pHCaCl2 3.2 adult survival was inhibited and no juveniles were produced, while at pHCaCl2 3.8 reproduction was also reduced. Bioaccumulation of Pb linearly increased with increasing total soil Pb concentrations. The grassland soils with pHCaCl2 > 6.5 and total Pb concentrations 355–656 mg/kg dw were least toxic. This study shows that E. crypticus was very sensitive to acidic soils with pHCaCl2 ≤ 3.8, suggesting that the toxic effects in the most contaminated forest soils may have been due to the low soil pH rather than the high Pb concentrations.
Toxicity profiles of two soils (a brownfield in Legazpi and an abandoned iron mine in Zugaztieta; Basque Country) contaminated with several metals (As, Zn, Pb and Cu in Legazpi; Zn, Pb, Cd and Cu in Zugaztieta) and petroleum hydrocarbons (in Legazpi) were determined using a multi-endpoint bioassay approach. Investigated soils exceeded screening values (SVs) of regulatory policies in force (Basque Country; Europe). Acute and chronic toxicity bioassays were conducted with a selected set of test species (Vibrio fischeri, Dictyostelium discoideum, Lactuca sativa, Raphanus sativus and Eisenia fetida) in combination with chemical analysis of soils and elutriates, as well as with bioaccumulation studies in earthworms. The sensitivity of the test species and the toxicity endpoints varied depending on the soil. It was concluded that whilst Zugaztieta soil showed very little or no toxicity, Legazpi soil was toxic according to almost all the toxicity tests (solid phase Microtox®, D. discoideum inhibition of fruiting body formation and developmental cycle solid phase assays, lettuce seed germination and root elongation test, earthworm acute toxicity and reproduction tests, D. discoideum cell viability and replication elutriate assays). Thus, albeit both soils had similar SVs, their ecotoxicological risk, and therefore the need for intervening, was different for each soil as unveiled after toxicity profiling based on multiple endpoint bioassays. Such a toxicity profiling approach is suitable to be applied for scenario-targeted soil risk assessment in those cases where applicable national/regional soil legislation based on SVs demands further toxicity assessment.
Mining activities can cause severe soil pollution in mining area and its surroundings. Nevertheless, very little is known about the local environmental risk after the mining activities are ended in China. Earthworms and soil microbial biomass carbon (SMBC), which are often used as bioindicators of soil pollution, were studied in order to support chemical analyses in assessing the status of soil heavy metal pollution around an abandoned copper mine in eastern Nanjing, China. Seven earthworm species belonging to three families (Megascolecidae, Moniligastridae, and Lumbricidae) were present. Correlations between earthworm densities or biomass and a range of soil physical and chemical parameters were generally poor; however, several linear regression models based on the soil physicochemical characteristics and metal concentrations in earthworm bodies were established for each metal (Cu, Cd, and Zn) and each earthworm family. Therefore, metal bioaccumulation by soil-dwelling earthworms can be used as an ecological indicator of metal availability for this area. The SMBC, which varied from 83.9 to 499 g kg−1, did not correlate with the soil heavy metal concentrations, and SMBC is not proposed as a sensitive indicator for evaluating the environmental effects of soil heavy metal pollution in this area.
To improve risk estimates at the screening stage of Ecological Risk Assessment (ERA), short duration bioassays tailored to undisturbed soil cores from the contaminated site could be useful. However, existing standardized bioassays use disturbed soil samples and often pH sensitive organisms. This is a problem as naturally acidic soils are widespread. Changing soil properties to suit the test organism may change metal bioavailability, leading to erroneous risk estimates. For bioassays in undisturbed soil cores to be effective, species able to withstand natural soil properties must be identified. This review presents a critical examination of bioassay species' tolerance of acidic soils and sensitivity to metal contaminants such as Pb and Zn. Promising organisms include; Dendrobaena octaedra, Folsomia candida, Caenorhabditis elegans, Oppia nitens, Brassica rapa, Trifolium pratense, Allium cepa, Quercus rubra and Acer rubrum. The MetSTICK test and the Bait lamina test were also identified as suitable microorganism tests.
Purpose
Soil properties are the main explanation to the different toxicities obtained in different soils due to their influence on chemical bioavailability and the test species performance itself. However, most prediction studies are centred on a few soil properties influencing bioavailability, while their direct effects on test species performance are usually neglected. In our study, we develop prediction models for the toxicity values obtained in a set of soils taking into account both the chemical concentration and their soil properties.
Materials and methods
The effects on the avoidance behaviour and on reproduction of the herbicide phenmedipham to the collembolan Folsomia candida is assessed in 12 natural soils and the Organisation for Economic Co-operation and Development (OECD) artificial soil. The toxicity outcomes in different soils are compared and explanatory models are constructed by generalised linear models (GLMs) using phenmedipham concentrations and soil properties.
Results and discussion
At identical phenmedipham concentrations, the effects on reproduction and the avoidance response observed in OECD soil were similar to those observed in natural soils, while effects on survival were clearly lower in this soil. The organic matter and silt content explained differences in the avoidance behaviour in different soils; for reproduction, there was a more complex pattern involving several soil properties.
Conclusions
Our results highlight the need for approaches taking into account all the soil properties as a whole, as a necessary step to improve the prediction of the toxicity of particular chemicals to any particular soil.
An experiment was conducted to evaluate the effect of zinc (Zn) rates and vermicompost levels on distribution of Zn forms of a calcareous soil. After incubation periods, soil samples were air dried, and a sequential extraction scheme was used to fractionate Zn into soluble and exchangeable, bound to carbonate, organically bound, bound to manganese (Mn) oxide, bound to amorphous iron (Fe) oxide, bound to crystalline Fe oxide, and residual forms. In untreated soil, Zn was mainly in the residual fraction. Increasing rates of applied Zn significantly increased all forms of Zn. Carbonate and residual forms showed the greatest increase. Application of vermicompost significantly increased all fractions except Mn-oxide form. This increase was more pronounced for organically bound, soluble, and exchangeable forms, indicating an increase in bioavailability of soil Zn. Incubation time significantly decreased soluble, exchangeable, and organically bound forms but increased other forms of Zn, meaning a significant reduction in Zn phytoavailability in soil with time.
Background, aim, and scopeSewage sludge use in agriculture should be limited by the presence of metals and other persistent environmental pollutants.
The present study aims to contribute for the definition of a test battery of ecotoxicological assays that allows a proper
ecotoxicological characterization of sludges, providing information on their potential hazard and identified “safe” application
levels.
Materials and methodsThree sludges from distinct sources (urban, olive-processing, and electroplating industries) were tested using avoidance and
reproduction tests with earthworms (Eisenia andrei) and springtails (Folsomia candida) and plant growth tests with turnips (Brassica rapa) and oats (Avena sativa). Different soil–sludge mixture concentrations mimicking recommended/realistic field dosages were tested.
ResultsOnly the sludge from the electroplating industry induced an avoidance response from the earthworms (EC50 = 0.4t/ha) and collembolans (no observed effect concentration (NOEC) = 15t/ha). This sludge was the only sludge responsible
for any effect on the reproductive output of the earthworms (EC50 = 7.74t/ha). Regarding collembolans, none of the sludges tested caused any significant decrease in reproduction. In higher
plant tests, the two industrial sludges were toxic, causing a decrease growth in both species. The EC20 values determined for B. rapa were 20.3 and 24.2t/ha and for A. sativa 14.7 and 16.2t/ha for sludges from olive-processing and electroplating industries, respectively.
DiscussionThe metal loadings of the different test sludges could partially explain the results obtained. The toxicity of the test sludge
from electroplating industry observed on the tested invertebrates and plants could be explained by the high amount of total
chromium from which 22.3% was in the most toxic oxidation state—Cr(VI). However, the toxicity caused by the sludge from the
olive-processing industry in the test plants could be attributed to the presence of other compounds (not measured in this
study) since the metal content was not high enough to induce such an effect. The absence of toxicity showed by the urban test
sludge was in agreement with its low levels of metals.
ConclusionsThe response of the different test organisms and end points varied according to the sludge type. The urban sludge was non-toxic
whereas the sludge from the electroplating industry caused a toxic effect on almost all parameters measured (avoidance behavior
of both test organisms, reproduction of earthworms, and growth of both plant species). Sludge from the olive-processing industry
only caused a toxic effect on growth of both plant species. By analyzing the sensitivity of the different parameters for the
most toxic sludge, it was found that avoidance and reproduction were more sensitive than plant growth, whereas plant seed
germination was not sensitive at all.
Recommendations and perspectivesThe ecotoxicological evaluation of wastes can be used as an environmental safety control of sludge use in agriculture. A tiered
approach could be adopted for this purpose, incorporating avoidance tests in the first tier (screening level) and reproduction
and plant growth tests in a second tier. But more evidence aiming to define the most suitable ecotoxicological test battery
for specific sludges with a different contamination profile is still needed.
Contamination by cadmium in the environment is of great concern because of its toxicity and threats to human and animal health. The current study was conducted to investigate the effects of a cadmium contaminated diet on the osmoregulation and urine concentration mechanisms of the semi-desert rodent Meriones shawi and eventual accumulation of this metal in vital organs such as the kidneys, which are directly implicated in water regulation. Originally, we used Differential Pulse Anodic Stripping Voltammetry (DPASV) to avoid the matrix interference due to the highly organic content in the biological samples. Our results show that Meriones shawi successfully maintained a homeostasis state and presented a special adaptation to regulate urine volume during cadmium exposure by decreasing diuresis and increasing urinary osmolality. The plasma osmolality and hematocrit remained constant throughout the experiment. The stripping signals of cadmium are linear up to 0.3-100 μg L(-1) range, with a detection limit of 0.28 μg L(-1). The DPASV technique was useful for easy, fast, selective and sensitive determination of Cd, which permits working at cellular concentration. This gives us more information about the chemical form in which Cd is introduced into the organ, as well as the intracellular Cd quantities. This study has potential importance if this valuable novel animal model, imitating human and animal environmental chronic exposure to Cd, could serve as an appropriate terrestrial biomonitor for Cd contaminated sites. These results are encouraging in the context of developing a low-cost and fast technology for the detection of pollutants and for studying the impairment caused by their effects.
The reproduction test with the collembolan Folsomia candida is used as a tool to evaluate the ecotoxicological potential of organic wastes currently applied to soil. Seven organic wastes (dewatered sewage sludges, thermally dried sewage sludges, composted sewage sludges, and a thermally dried pig slurry) were tested. These wastes had different origins, treatments, and pollutant burdens, and were selected as a representative sample of the wide variety of wastes currently generated. F. candida showed varied sensitivity depending on the waste, but also depending on the endpoint assessed. Reproduction was more sensitive than survival, although no correlations between reproduction and physico-chemical parameters and pollutant burden could be found. On the other hand, mortality was directly related to the lack of stability of wastes, probably reflecting the toxicity of end-products such as ammonium. Body length was not shown to be a sensitive endpoint for waste testing, as it was neither affected nor even stimulated by waste concentrations.
This report describes a research on the use of enchytraeids in soil ecotoxicology. Actually many soil ecotoxicological research is restricted to the earthworm Eisenia andrei/fetida limiting possibilities for generalisation and ecologically relevant test results. This study on enchytraeids consits of a literature survey and experimental work. The influence of soil moisture, pH, temperature on the reproduction of enchytraeids, and methods for breeding and isolating enchytraeids are studied. The experimental work focusses on two species, Enchytraeus albidus and E. crypticus, laboratory cultures of both species are obtained from other institutes. For both species reproduction tests could be performed in OECD-artificial soil. It is concluded that reproduction experiments with enchytraeids are applicable within the actual research program of the Department of Soil Ecotoxicology.
The behaviour of a chemical in a soil or sediment depends on its physical-chemical properties as well as on the environmental conditions prevalent in its immediate surroundings. In soils and sediments, contaminant behaviour may be determined by the content of organic matter, clay, and hydroxides of aluminium and iron and by pH (Alleyway 1990; Bolt and Bruggenwert 1976; Van Riemsdijk and Hiemstra 1993; Yong et al. 1992). These properties determine the storage capacity of soils for heavy metals and other pollutants, and are therefore called Capacity Controlling Parameters (CCP) (ter Meulen et al. 1993). The same properties are believed to determine bioavailability of contaminants for organisms living in soil or sediment.
Description
A pioneer attempt to assess the safety of chemicals that directly of indirectly affect water based ecosystems. 22 papers provide state-of-the-art for research approaches, new applications of old methods, new data on several pesticides and other chemicals.
The capacity to reproduce is an essential factor for the long-term survival of populations at the basis of the food web. Ecological effects of soil pollutants may be assessed in terms of exposure levels that reduce reproduction, relative to survival. In this study, the earthworm Aporrectodea caliginosa (Annelida, Oligochaeta) was exposed to cadmium, copper and zinc in a natural soil. Each metal was mixed into the soil, as a sulphate salt, in a different series of concentrations. Mortality and cocoon production were measured over 56 days to determine LC50, EC50 and EC10 values for each metal separately. LC50 decreased with exposure time and it approached a constant value for each metal. EC50 and EC10 values were determined following a loglogistic curve fitting of cocoon production versus exposure concentration. The ratio between the LC50 and the EC10 for effects on reproduction (sublethal sensitivity index, SSI), was different for each metal. The ratio was greatest for cadmium (a factor of 300) and smallest for zinc and copper (a factor of 6 to 10). Based on the single metal EC50s a mixture of the three metals was prepared and effects on cocoon production were assessed. The EC50 of the mixture was 1.4 toxic units and this value differed significantly from 1. It may be concluded that 1) SSI is highly metal-specific, and 2] the three metals, cadmium, copper and zinc, in the concentration levels tested, have an antagonistic fiction on each other in their effects on cocoon production of Aporrectodea caliginosa.
The influence of food supply on the toxicity of zinc was investigated for the springtail Folsomia candida in an attempt to identify factors that might modulate ecotoxicological effects of soil contaminants. Animals were incubated in zinc contaminated soil at four different food regimes. The first group was fed dried baker's yeast which was supplied on top of the test soil. For the second treatment, yeast was mixed homogeneously in with the soil, the third group of animals received pollen grains for food, and for the last treatment, no additional food was added during the toxicity experiment. Animals that received yeast on top of the soil were less able to regulate the internal zinc concentration and were most sensitive to zinc when growth or reproduction were regarded. Reproduction was affected when animals were still able to regulate the internal zinc concentrations. Effect concentrations were not significantly different from the pollen treatment. In the other two treatments, growth was not affected by zinc but reproduction was severely affected by the absence of available food. It was concluded that both zinc stress and food shortage have a major influence on population development of Folsomia candida, whereas the interaction between food supply and zinc toxicity is small.
Nine toxicity tests were conducted using a procedure based on the OECD (1984) artificial soil earthworm toxicity test. For each test, Eisenia fetida were exposed to zinc in a range of artificial soils with differing pH and/or organic matter (OM) content. Earthworm survival and cocoon production, and the concentrations of zinc in two fractions (nitric acid extractable, water extractable) and the exposed earthworms were measured. The proportion of total zinc that was soluble was greater in soil with low pH and low OM content. Zinc burdens were greatest in worms maintained in the most contaminated soils. However, the slopes of the relationships between earthworm zinc concentrations and zinc concentrations in soils (total and soluble) were less than one indicating probable regulation of net assimilation of this essential element by Eisenia fetida. Toxic effects of zinc on Eisenia fetida as measured by reductions in survival and cocoon production were related more closely to soluble than total metal concentrations in soil. In a previous series of tests, zinc toxicity for Eisenia fetida was found to be at least ten times greater in OECD artificial soil when compared to contaminated soils collected from a polluted field site (Spurgeon & Hopkin, 1995). It was concluded that this was due to the greater bioavailability of the metals in the OECD soil. The results of the present paper support this hypothesis.
: The effects of cadmium, copper, lead and zinc on survival, growth, cocoon production and cocoon viability of the earthworm Eisenia fetida (Savigny) were determined in three experiments. In experiment 1, worms were exposed to single metals in standard artificial soil. For experiment 2, worms were maintained in contaminated soils collected from sites at different distances from a smelting works situated at Avonmouth, south-west England. In experiment 3, worms were exposed to mixtures of metals in artificial soil at the same concentrations as those present in the field soils. A survey of earthworm populations was carried out also. Population densities and species diversities of earthworms declined with proximity to the smelting works. No earthworms were found within 1 km of the factory. Comparison of toxicity values for the metals determined in the experiments indicated that zinc is most likely to be limiting earthworm populations in the vicinity of the works. Zinc was at least ten times more toxic to E. fetida in artificial soil than in contaminated soils collected from the field. This difference was probably due to the greater bioavailability of zinc in the artificial soil. The results are discussed in the context of setting 'protection levels' for metals in soils based on laboratory toxicity data.
The use of toxicity tests in which each chemical is tested separately is inadequate for assessing the potential risk of complex mixtures of chemicals for soil ecosystems. In the present study, the effects of Cd and Zn, alone or in combination, on the survival, growth, and reproduction of the collembolan Folsomia candida were determined after 2, 4, and 6 weeks of exposure in an artificial soil. The water solubility of Cd in the soil was significantly increased by the presence of Zn, whereas Cd did not affect the water solubility of Zn. In spite of this, uptake of Cd or Zn in the animals was not affected by the presence of the other metal, suggesting that water solubility does not determine the uptake of these metals in F. candida. For both Cd and Zn, reproduction was the most sensitive parameter, with 50% effective concentration (EC50) values of 51 and 683 {micro}g/g dry soil, respectively, after 6 weeks. These values corresponded with internal concentrations of 44 {micro}g Cd/g and 14 {micro}g Zn/g dry soil, respectively. Although a proper comparison of the effects of mixtures of the metals with the effects of the individual metals was sometimes hampered by the nonsimilarity of dose-response relationships, it may be concluded that the effects of the mixture of Cd and Zn on the growth of F. candida are antagonistic (EC50 significantly greater than 1.0 toxic unit), while the effects on reproduction are additive (EC50 = 1.0 toxic unit). Similar conclusions could be drawn for EC50s expressed on the basis of total and water-soluble soil concentrations as well as on the basis of internal concentrations in animals. Analysis of the combined effects of Cd and Zn at the 10% effective concentration level did not change these conclusions.
Accumulation and elimination of cadmium, chromium and zinc and effects on the growth and reproduction of the earthworm Eisenia andrei were determined in an artificial soil. Cadmium at the lowest soil concentration tested (10 mg/kg) significantly reduced cocoon production, whereas cadmium concentrations in the earthworms at the end of the 3-week exposure period were significantly increased in a dose-related manner at all concentrations tested. Reproduction was completely recovered at the end of a 3-week recovery period in untreated soil, although cadmium concentrations in the earthworms were still significantly elevated. Apparently, the remaining cadmium residues in the worms were strongly bound, and therefore no longer exerted a toxic effect on the reproduction of earthworms. Chromium was significantly accumulated and earthworm reproduction significantly reduced at soil concentrations of 100 mg/kg and higher. Chromium was completely eliminated and reproduction no longer affected at the end of a 3-week recovery period. Zinc significantly reduced reproduction at soil concentrations of 560 and 1000 mg/kg, and induced the production of malformed cocoons. Earthworms were able to regulate their body content of zinc; only at 1000 mg/kg dry soil were zinc concentrations significantly increased. At the end of a 3-week recovery period zinc concentrations in the earthworms had returned to the control level, and reproduction was completely recovered.
Soil properties are a major influence on the bioavailability and toxicity of metals and represent one of the important factors that complicate the extrapolation of results from laboratory tests to field situations. The influence of soil characteristics and way of contamination on the bioaccumulation and toxicity of zinc was investigated for the springtail Folsomia candida, and the applicability of chemical extraction techniques for the prediction of zinc uptake and toxicity was evaluated. Bioaccumulation of zinc in F. candida was related to water-soluble zinc concentrations, and uptake was dependent on the test soil used. Effects of zinc for F. candida could not be fully explained by bioaccumulation. This indicates that the existence of a fixed internal threshold concentration of zinc above which physiological functions are impaired is not likely for F. candida. In freshly contaminated soils, zinc toxicity was related to organic matter and clay content of the soil; however, the use of these soils overestimated the effects of zinc for F. candida by a factor of 5 to 8 compared to a test soil that was subjected to ageing under field conditions for 1.5 years. Equilibration of the zinc contamination by percolating the soils with water before use in the toxicity experiment strongly reduced the difference in zinc toxicity between laboratory-treated and aged soils. Water-soluble concentrations are most appropriate to predict effects of zinc on reproduction of F. candida in soils with unknown contamination histories. For laboratory toxicity tests, it is recommended to percolate soils with water after contamination and to include an equilibration period prior to use to achieve a more realistic exposure situation.
Multivariate test designs were used to identify and quantify the soil parameters important for determining the ecotoxicological effects of zinc and cadmium to the potworm Enchytraeus albidus. The application of a fractional factorial design (FFD) revealed that the acute toxicity of zinc and cadmium to E. albidus can vary over more than two orders of magnitude, depending on the composition of the (artificial) soils. The differences in metal ecotoxicity were determined mainly by pH and organic matter content or cation exchange capacity (CEC). Using a central composite design, models were developed describing the ecotoxicity of zinc and cadmium to E. albidus as a function of these parameters. To validate the developed surface response models, two field soils and the standard artificial soil prescribed by the Organization for Economic Cooperation and Development (OECD) were spiked with zinc and cadmium, and the acute toxicity to E. albidus was assessed. These validation experiments confirmed that the toxicity of zinc and cadmium could be predicted by the pH and the CEC of a soil with toxicity decreasing with increasing pH and CEC.
Life-cycle (survival, weight change, and cocoon production rate) and biomarker (neutral-red retentionby coelomocytes lysosomes) responses to zinc in four earthworm species were measured in laboratory tests. In all species, dose-dependent effects on survival, cocoon production, and neutral-red retention times were found (one-way ANOVA p < 0.05). However, for weight change, only Aporrectodea caliginosa showed a clear response. Comparisons of the effects of zinc on these parameters in the different earthworm species indicated similar order of sensitivity. Thus, Lumbricus rubellus and Aporrectodea caliginosa were more sensitive to zinc than Lumbricus terrestris and Eisenia fetida in all cases. To compare the relative sensitivities of life-cycle and biomarker responses, a sublethal sensitivity index (SSI) was applied. For cocoon production, SSIs indicated that the EC10s were below LC50s by a factor of between 8.3 and 16.5. These values are toward the high end of the range found previously for soil invertebrates, indicating an emphasis on maximizing survival. For neutral red, SSIs ranged from 4.5 to 41.2. Thus, the biomarker was predictive of life-cycle effects in some (Lumbricus rubellus and Aporrectodea caliginosa), although not the other two species tested.
The use of toxicity tests in which each chemical is tested separately is inadequate for assessing the potential risk of complex mixtures of chemicals for soil ecosystems. In the present study, the effects of Cd and Zn, alone or in combination, on the survival, growth, and reproduction of the collembolan Folsomia candida were determined after 2, 4, and 6 weeks of exposure in an artificial soil. The water solubility of Cd in the soil was significantly increased by the presence of Zn, whereas Cd did not affect the water solubility of Zn. In spite of this, uptake of Cd or Zn in the animals was not affected by the presence of the other metal, suggesting that water solubility does not determine the uptake of these metals in F. candida. For both Cd and Zn, reproduction was the most sensitive parameter, with 50% effective concentration (EC50) values of 51 and 683 μg/g dry soil, respectively, after 6 weeks. These values corresponded with internal concentrations of 44 μg Cd/g and 97 μg Zn/g dry body weight, respectively, while corresponding water-soluble EC50s were 0.13 μg Cd/g and 14 μg Zn/g dry soil, respectively. Although a proper comparison of the effects of mixtures of the metals with the effects of the individual metals was sometimes hampered by the nonsimilarity of dose-response relationships, it may be concluded that the effects of the mixture of Cd and Zn on the growth of F. candida are antagonistic (EC50 significantly greater than 1.0 toxic unit), while the effects on reproduction are additive (EC50 = 1.0 toxic unit). Similar conclusions could be drawn for EC50s expressed on the basis of total and water-soluble soil concentrations as well as on the basis of internal concentrations in the animals. Analysis of the combined effects of Cd and Zn at the 10% effective concentration level did not change these conclusions.
A previously developed soil toxicity test for rapidly determining the toxicity of chemicals to the soil-dwelling nematode Caenorhabditis elegans (Donkin and Dusenbery, 1993) was used to measure the toxicity of four metals (Zn2+, Cd2+, Cu2+, and Pb2+) added to four soils common to the southeastern United States. Nematode survival after a 24-hour exposure in the presence of a bacterial food source was assessed. All soils reduced the toxicity of most metal ions compared to solutions without soil. Pb was the most strongly affected, while Cd toxicity was not much influenced by the soils. Correlations between the LC50S and various soil or metal characteristics were determined. No significant correlation was found between LC50s and many soil characteristics commonly cited as having large effects on soil bioavailability of metals. Although sample size was limited, the indication was that bioavailability of metals to nematodes is determined by a complex array of many interacting soil, as well as metal, properties. Comparison of the relative mobilities of these ions in other soils with the relative toxicity measured here suggests that mobility may be a good predictor of toxicity. The C. elegans soil toxicity test is shown to be as sensitive and more rapid than the commonly used earthworm soil toxicity test.
Development of methods to measure the effect of man's residuals on soil ecosystems is desirable. Earthworms, as one of the largest and most easily obtained components of the soil biota, are suitable for evaluating perturbations to soil ecosystems.
The impact of five metals (Cd, Cu, Ni, Pb, and Zn) on the survival of the earthworm Eisenia fetida (Savigny) was evaluated using the contact and artificial soil tests. There was no difference in toxicity between the different metal salts (acetate, chloride, nitrate, and sulfate) of each of the five metals using the contact test. In the contact test, the order of toxicity, from most toxic to least toxic, was Cu > Zn > Ni ≈ Cd > Pb. The nitrate salt of the five metals was tested using the artificial soil test and the order of toxicity, from most toxic to least toxic, was Cu ≈ Zn ≈ Ni > Cd > Pb. Stress on earthworm populations, as shown by weight loss, was shown to increase with increasing concentrations of metal salts.
These studies indicate that: (a) earthworms can be a suitable biomonitoring tool to assist in measuring the effect of metals in wastes added to soils and (b) the contact and artificial soil tests can measure the biological impacts.
To evaluate the influence of soil characteristics and chemical application form on the ecotoxicity of zinc, the toxicity of contaminated soil samples from the vicinity of a zinc smelter was compared with the effects of ZnCl2 added to two uncontaminated natural soils. Tests were performed with the springtail Folsomia candida (Willem).In the artificially contaminated soils, ZnCl2 had a strong effect on reproduction, whereas the effects on growth were not conclusive. In the polluted field soil however, no relationship was observed between zinc concentrations and growth or reproduction. Chemical analysis of the soils used showed that water soluble concentrations were higher in the artificially contaminated soils than in the polluted field soil. However, differences in water soluble zinc concentrations could not fully explain the differences in effects among the soils.It is concluded that because of the influence of soil type and chemical form of zinc on bioavailability and toxicity, artificially contaminated soils should be used with caution in ecotoxicological risk assessment. It is recommended to include soil pore water analysis in future research to improve the interpretation and application of results obtained in artificially contaminated soils.
The effects of metal contaminants on the population density and species composition of earthworms were studied at 22 sites around a primary smelting works situated at Avonmouth, southwest England. All worms were absent from six sites within 1 km of the factory and numbers were also reduced significantly at an additional four sites 2 km from the plant. Total earthworm density was found to be inversely related to concentrations of metals in soils. some species of earthworms were found to be more ‘sensitive’ to metals and were absent from sites where more ‘tolerant’ species persisted. For example, Lumbricus rubellus, Lumbricus castaneus and Lumbricus terrestris were all present at sites close to the smelter where Aporrectodea rosea, Aporrectodea caliginosa and Allolobophora chlorotica were absent. The first three ‘tolerant’ species have more active calcium secretion glands in their gut than the three ‘sensitive’ worms. Calcium is known to be involved in the sequestration and elimination of various metals through the chlorogogenous tissue.
This article describes a standardized test method for determining the effect of chemical substances on the reproduction of the earthworm Eisenia fetida andrei. It is based on the existing guidelines for acute toxicity testing with earthworms, and for reasons of standardization the same artificial soil substrate and earthworm species were chosen as prescribed by these guidelines. After being preconditioned for one week in untreated soil, earthworms are exposed to the chemical substances for 3 weeks. The number of cocoons produced is determined, and cocoons are incubated in untreated artificial soil for 5 weeks to assess hatchability. Results are presented from toxicity experiments with pentachlorophenol, copper, and 2,4-dichloroaniline. For these compounds no-effect levels (NEL) for cocoon production were 32, 60-120, and 56 mg.kg-1 dry soil, respectively. Hatching of cocoons was influenced by pentachlorophenol (NEL, 10 mg.kg-1), but not by copper and dichloroaniline. Following exposure, earthworms were incubated in clean soil again to study the possibility of recovery of cocoon production. For copper and dichloroaniline earthworms did recover cocoon production to a level as high as the control level or even higher; in case of pentachlorophenol, cocoon production was still reduced after 3 weeks in clean soil.
To implement the Soil Protection Act of 1986, the Dutch Ministry of Housing, Physical Planning, and Environment has recently proposed a list of soil quality reference values. These values are, as yet, insufficiently based on ecotoxicological evidence. In this paper, a three-step procedure of risk assessment for soil contaminants is proposed. Arguing from experimental results concerning no observed effect concentrations for a set of selected soil organisms, the method aims at protecting a certain fraction of soil life, taking factors such as soil organic matter and clay content into account. When applied to cadmium, a concentration protecting 95% of soil invertebrates is estimated as 0.16 micrograms/g for a standard soil. The value of 0.8 micrograms/g, as proposed by the Dutch authorities, may, given the present variation and uncertainty of toxicity data, protect about 85% of the soil invertebrate fauna. It is concluded that even low levels of cadmium in soil may endanger the functioning of some sensitive soil animal species.
This paper deals with the calculation of Hazardous Concentrations of toxic substances from small sets of laboratory toxicity data, e.g., NOECs. A procedure due to Van Straalen and Denneman, as adapted from Kooijman (case n = 1), in which one seeks a concentration that protects 95% of the biological species is modified to account for the uncertainty in the estimates. New constants are obtained by simulation. These allow the calculation of the one-sided 95% left confidence limit of the Hazardous Concentration, from the mean and standard deviation of a sample of (laboratory) toxicity data. This 95% confidence limit is always lower than the 95% certainty value calculated with the Kooijman (n = 1)/Van Straalen method. The authors also derive constants to calculate a one-sided 50% confidence value, that overpredicts as often as it underpredicts. This value may be used as a median guess of the Hazardous Concentration. It will always be higher than the 95% certainty value of the Kooijman (n = 1)/Van Straalen method. However, by using the 50% value, one runs the risk of protecting substantially less than 95% of the biological species.
EC50s for cadmium, copper, lead and zinc were determined for juvenile production of Folsomia candida at pH6.0, 5.0 and 4.5 in a standard laboratory test system. In contrast to most previous studies where metal toxicity was increased at low pHs, in our experiments there was no clear relationship between soil acidity and EC50-reproduction in this species. The EC50-reproduction values (microgram g-1) for cadmium and zinc were similar at all three pHs (pH6.0: Cd 590, Zn 900; pH5.0: Cd 780, Zn 600; pH4.5: Cd 480, Zn 590). In contaminated field sites adjacent to primary zinc smelters, zinc is invariably present in soils at concentrations of at least 50 times that of cadmium. Thus deleterious effects of mixtures of these metals on populations of Collembola in such sites can be attributed to zinc rather than cadmium.
A range of toxicity tests have been proposed to assess the potential hazards of pollutants to earthworms. Of these, the two acute toxicity tests using Eisenia fetida recommended by the OECD and EEC have become routinely used in the risk assessment and regulation of new and existing chemicals. In addition to the acute tests, procedures have also been proposed for measuring the sub-lethal effects of chemicals on parameter such as reproduction and weight change. In both the lethal and sub-lethal toxicity tests developed with worms, attempts have been made to standardise test conditions to allow results from different laboratories to be directly compared. However, variability in exposure conditions and responses are fundamental to determine the effects of pollutants under natural conditions. In the field, conditions such as light, moisture availability, pH, temperature and humidity all fluctuate over time. Such variations affect both the sensitivity and exposure of individuals to toxic chemicals. Hence when evaluating the potential effects of pollutants, it may be important to known how changes in test conditions influence toxicity. This study assessed the effects of different temperatures on the lethal and sub-lethal toxicity of zinc for the earthworm Eisenia fetida. 23 refs., 1 fig., 1 tab.
EC50s for cadmium, copper, lead, and zinc were determined for juvenile production of Folsomia candida Willem, 1902, at 25, 20, and 15 degrees C in a standard laboratory test system. Juvenile production of F. candida was too low at 25 degrees C for reliable EC50-reproduction values to be determined. The EC50-reproduction values (micrograms g-1) for cadmium, copper, and zinc were similar at both 20 and 15 degrees C (20 degrees C: Cd, 590; Cu, 700; Zn, 900; 15 degrees C: Cd, 540; Cu, 640; Zn, 590). Corresponding values for lead were considerably higher (20 degrees C: Pb, 2790; 15 degrees C: Pb, 1570). In aerially contaminated field sites adjacent to primary zinc smelters, zinc is invariably present in surface soils at concentrations of at least 50 times those of cadmium. The similarity of the EC50-reproduction values for cadmium and zinc in F. candida at 20 and 15 degrees C determined in this study strongly suggests that deleterious effects of mixtures of these metals on populations of Collembola in such sites can be attributed to zinc rather than cadmium.
A unified method is presented to derive maximum permissible concentrations (MPCs) of xenobiotic and naturally occurring substances. The method relies upon risk limitation expressed as the maximum potentially affected fraction of all possible species (PAFmax) in a component ecosystem, due to a bioavailable concentration of the considered substance. For xenobiotic compounds the method is simplified to the "HC5 approach," i.e., the MPC equals the hazardous concentration at which 5% of the species are unprotected. If the natural background of a substance is (partly) bioavailable, the related background effect, also expressed as PAF, is taken into account in deriving a MPC. Examples are given and MPCs for zinc, chromium, cadmium, copper, and lead for different levels of bioavailability in water are developed.
To generate reproducible and reliable results, most protocols for standardized toxicity tests prescribe strict limits for test conditions such as temperature and relative humidity. In the field, however, variability of climate can influence the functioning of organisms and induce changes in sensitivity. To evaluate the influence of temperature on the ecotoxicity of zinc, the springtail Folsomia candida was exposed to zinc-contaminated soil at different temperatures. In one experiment, the toxicity of ZnCl2 was determined at a constant temperature and under alternating temperature conditions. Although control performance of F. candida was influenced by the temperature treatment, effect concentrations for reproduction were not significantly different between treatments. Levels of internal zinc regulation were higher in animals exposed to alternating temperatures. Based on the observed influence of temperature on the accumulation of zinc, a second experiment was performed to determine the sensitivity of F. candida to zinc at four different exposure temperatures. A decrease in temperature led to an increase in sensitivity when sublethal parameters such as growth and reproduction were considered. However, animals were less sensitive at lower temperatures where mortality was concerned. Internal zinc concentrations in the animals increased with decreasing temperatures, and when the effect on reproduction was based on internal zinc levels, differences between temperature treatments were not significant. From the results of this study it is concluded that for F. candida, constant temperature conditions form a good basis for the extrapolation of toxicity levels to fluctuating temperature conditions. Since the average exposure temperature can alter the sensitivity of F. candida for zinc, and changes in sensitivity are parameter dependent, exposure temperature should be chosen carefully.
Joint toxic effects of copper and zinc were studied in the terrestrial worm Enchytraeus crypticus (Westheide and Graefe) (Oligochaeta, Annelida). Animals were exposed in OECD artificial soil. Sublethal toxicity was judged by effects on reproduction. Metals were applied singly or in binary mixtures. Observed effects were compared with effects expected from simple similar action (concentration addition), by recalculation of metal concentrations in toxic units. Exposure of the worms was quantified with body concentrations and with external concentrations (total, extractable, soluble). The observed joint effect was similar to concentration additive when judged by external concentrations and less than concentration additive for body concentrations. This difference is attributable to interactions among metals during sorption to soil and during uptake. Copper reduced the sorption of zinc to soil, but copper sorption was inert for zinc addition. Zinc uptake from the soil solution was stimulated by copper, but copper uptake was not stimulated by zinc. Joint effects of toxicants to soil biota are partly determined by interactions outside the organism, as a result of dissimilarity between total and bioavailable concentrations. The design of joint toxicity studies in terrestrial systems is discussed with special reference to metal sorption in soils, experimental methodology, and laboratory practice. The joint toxic effect of copper and zinc for E. crypticus was of similar magnitude as found in studies with aquatic species exposed to metal mixtures.
Clay and organic matter are considered as important parameters influencing bioavailability and ecotoxicity of metals in soils. As there exists a large variation in the type of clay and organic matter in field soils, the quantity of these variables alone may not be good indicators of metal bioavailability. To test this hypothesis, toxicity experiments with the potworm Enchytraeus albidus were conducted in artificial soils with three types of clay and seven types of organic matter, while the soil pH was kept constant. The 14d LC50 of zinc and cadmium varied from 83.0 to 1,140 mg Zn/kg D.W. and from 55.2 to 704 mg Cd/kg D.W., respectively, depending on the type of clay and organic matter that were used. Simultaneous measurements of the cation exchange capacity showed that this soil parameter is a better indicator of the bioavailability as it takes into account the type of clay and organic matter as well as other adsorption phases such as metal oxyhydroxides.
The earthworm Eisenia fetida (Annelida: Oligochaeta) was exposed to a geometric series of concentrations of cadmium, copper, lead and zinc in artificial soil using the OECD recommended protocol. Mortality, growth and cocoon production were measured over 56 days to determine LC50 and EC50 values. No observed effect concentrations (NOECs) were also estimated. Furthermore, the percentage of viable cocoons and number of juveniles emerging per cocoon was recorded. Cocoon production was more sensitive than mortality for all the metals, particularly cadmium and copper for which NOEC reproduction values were an order of magnitude lower than those for NOEC mortality. However, there was no significant effect of metals on the viability of cocoons. The weights of earthworms declined in all treatments (including the controls) during the experiment. This was probably due to the lack of suitable food in the OECD standard soil medium used. It was concluded that future experiments should include animal manure in the test medium. The LC50, EC50 and NOEC values determined in this study were compared with concentrations of metals in soils in the vicinity of a smelting works at Avonmouth, southwest England. The 14-day LC50 for zinc in Eisenia fetida was exceeded in soils covering an area of 75 km2 around the works, compared to 4.2 km2 for copper and 4.7 km2 for lead. Soil values for cadmium did not exceed the LC50 value anywhere in the region. Similar estimates of relative effects on reproduction confirmed that zinc is most likely to be responsible for the absence of earthworms from sites close to the Avonmouth works. However, the OECD standard test overestimated the potential effects of metals on populations, since earthworms can be found as close as 1 km from the smelting works. The discrepancy between test and field observations was probably due to the greater availability of the metals in the artificial soil.
The influence of outdoor exposure conditions and ageing of contamination on the toxicity of zinc was investigated for the springtail Folsomia candida to evaluate the validity of a standardised soil toxicity test. In three successive years, animals were incubated in an experimentally contaminated field plot. During the first months after construction of the test field, total zine concentrations of the soil decreased rapidly due to leaching of excess zinc with rainwater, while increased sorption of the remaining residues resulted in a reduced bioavailability of the metal. Although variation between replicates was substantial, the EC50s for the effect of zinc on reproduction of F. candida determined in the field experiments differed by less than a factor of two from effect concentrations obtained in laboratory tests in which the same soil was used. Expression of the EC50s on the basis of water soluble zinc allowed for a comparison with effect concentrations estimated for other soil types. EC50s were comparable with literature data, which indicates that bioavailability of zinc is the main factor determining toxicity for F. candida. It is concluded that laboratory based toxicity data are suitable to predict effects of zinc for F. candida under outdoor conditions, provided that the bioavailability of zinc is determined accurately using water soluble concentrations.
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