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Chemical forms and reactivities of metals in sediments
Abstract
Sediment analyses are used to pin-point major sources of pollutants and to estimate the toxicity potential of dredged material on agricultural land. For source assessment starndardization is needed with respect to grain size effects; various methods are described, e.g., extrapolation techniques, mineral corrections, mechanical fractionation, chemmical extraction of mobilie fractions of metals, comparison with conservative elements. Only paart of the metals present in sediments or sludges are involved in short-term geochemical processes and/or are bioavailable. Hydrous Fe- and Mn-oxides as well as organic matter, partly as coatings or films on detrital grains, are important substrates for the interactioons with dissolved metaö species in aquatic systems. For the differentiation of the relative bonding strength of metals on various solid phases and for the estimation of their potential reactivity under variable environmental conditions sequential extraction procedures were used. While these determinations seem to pose basically operational problems, the correlation of the data from solid speciation with the processes and extent of biological uptake is still unsatisfactory. This is maiinly due to the competition between sorption sites on solid matter and biological processes for dissolved metals. A uniform assessment scheme for the "bioavailability" can, therefore, not be established on the basis of extraction chemical data from sediment samples.
... Trace metals are introduced into the river water-sediment system through several complex natural and anthropogenic sources such as chemical weathering of source rocks, riverbank erosion processes, atmospheric particulate matter fall outs, industrial effluents, pesticides from agricultural fields, municipal wastes and sewerages etc. (Singh et al. 2008). Trace metals after their release from source areas enter the solid-liquid phases of the riverine systems in different proportions depending upon the physico-chemical conditions and river dynamics and exist in colloidal, particulate and dissolved phases (Forstner 1985 andLuoma 1990). ...
Krishna delta along the east coast of India presents a complex hydrogeological and hydrogeochemical situation with Holocene marine transgression events marked by paleo strand lines and subsequent evolutionary trends of the delta marked by numerous paleochannels/lobes. These paleochannels/lobes act as huge repositories for groundwater in the near surface aquifer systems with depth levels varying between 10 and 80 m bgl (below ground level) with high recharge potentials and are underlained by brackish water aquifers deposited during the marine transgressional events. These near surface aquifer systems have been subjected to over abstraction of groundwater to meet the irrigation and drinking water demands through multiple shallow well field systems resulting in vertical migration of brackish water and mixing with near surface freshwater aquifers. These processes are dominant in the regions with high abstractions and relatively low or insignificant mixing in the low abstraction and high recharge regions. Sixteen trace metals Beryllium (Be), Cobalt (Co), Strontium (Sr), Boron (B), Nickel (Ni), Molybdenum (Mo), Lead (Pb), Vanadium (V), Copper (Cu), Chromium (Cr), Zircon (Zn), Manganese (Mn), Arsenic (As), Iron (Fe), Selenium (Se) and Barium (Ba) were analyzed from the groundwater of the near surface aquifer systems at 29 sites covering the entire delta complex. Almost all the trace metals incorporated lie within safe and acceptable limits prescribed by WHO/BIS excepting Sr, B, Mo, Pb, V, Mn, As, and Fe located at few isolated sites due to localized pollution impacts prevailing in the low-lying delta regions. The spatial distributional trends, intensity levels and their impacts on natural/ anthropogenic processes are analyzed and presented. Pollution indices related to Contamination Factor (CF) and Pollution Load Index (PLI) are estimated and applied to arrive at different levels of contamination against each element. A number of graphical cross plots are also drawn between TDS and different trace metal levels to assess the trends of each element in relation to fresh and brackish water zones and their impacts on salinization and anthropogenic processes. Multivariate statistical analysis (correlation matrix and factor analysis) are also used to assess the natural/ anthropogenic impacts. The overall analysis indicates dominant brackish water mixing processes and low to moderate impacts due to several automobile units, agro-based fertilizer units, aqua forms, electro chemicals and coal-based industries in addition to municipal wastes and sewerage disposal sites existing in the delta region.
... The MVT deposits in the Benassal Formation contain the following minerals: galena (Pb-rich), sphalerite (Zn-rich), barite (Ba and S-rich), goethite and hematite (Fe-rich) and pyrite (S-rich) Martín-Martín et al. (2013). To explain the enrichment in Zn of the fluid but not Pb or Fe, interaction with the MVT deposits, an acidic fluid (pH < 7) can be invoked as the relative mobility of the Zn 2+ is much higher than Pb 2+ at low pH (Förstner, 1985). Additionally, the redox conditions of dedolomitization can be obtained using trace elements such as Mn, V and U (Chen et al., 2015;Huang et al., 2011;Zhang et al., 2014). ...
... As mentioned above, one promising approach for pollution assessment is based on the analysis of sediment cores (Bigus et al., 2014;Korosi et al., 2015). Due to variable accumulation of contaminants over time, depending on entry into the aqueous layer above and the contaminants' physical chemical properties, sediments serve as time records of aquatic systems' pollution and can thus serve as a powerful indicator for contaminant presence and allow the assessment of a time-integrated pollution status (Bigus et al., 2014;Förstner, 1985;Johannessen and MacDonald, 2012;Korosi et al., 2015). Several powerful examples exist for the application of sediment cores to reconstruct pollution over time, for example monitoring the beginning of industrialization or contamination phase-outs (Arp et al., 2011;Combi et al., 2019;Götz et al., 2007;MacInnis et al., 2019;Pérez-Fernández et al., 2016;Peters et al., 2020;Shahabi-Ghahfarokhi et al., 2020;Sobek et al., 2015); however, the technique requires that sediment layers are not disturbed by bioturbation, sediment transport processes, or other processes that disturb regular sediment deposition (Johannessen and MacDonald, 2012;Noji et al., 2002). ...
The North Sea and its coastal zones are heavily impacted by anthropogenic activities, which has resulted in significant chemical pollution ever since the beginning of the industrialization in Europe during the 19th century. In order to assess the chemical Anthropocene, natural archives, such as sediment cores, can serve as a valuable data source to reconstruct historical emission trends and to verify the effectiveness of changing environmental legislation. In this study, we investigated 90 contaminants covering inorganic and organic pollutant groups analyzed in a set of sediment cores taken in the North Seas' main sedimentation area (Skagerrak). We thereby develop a chemical pollution fingerprint that records the constant input of pollutants over time and illustrates their continued great relevance for the present. Additionally, samples were radiometrically dated and PAH and PCB levels in porewater were determined using equilibrium passive sampling. Furthermore, we elucidated the origin of lead (Pb) contamination utilizing non-traditional stable isotopic analysis. Our results reveal three main findings: 1. for all organic contaminant groups covered (PAHs, OCPs, PCBs, PBDEs and PFASs) as well as the elements lead (Pb) and titanium (Ti), determined concentrations decreased towards more recent deposited sediment. These decreasing trends could be linked to the time of introductions of restrictions and bans and therefor our results confirm, amongst possible other factors, the effectiveness of environmental legislation by revealing a successive change in contamination levels over the decades. 2. concentration trends for ΣPAH and ΣPCB measured in porewater correspond well with the ones found in sediment which suggests that this method can be a useful expansion to traditional bulk sediment analysis to determine the biologically available pollutant fraction. 3. Arsenic (As) concentrations were higher in younger sediment layers, potentially caused by emissions of corroded warfare material disposed in the study area after WW II.
... Trace metal concentration in the sediments often reflects their lithological source (Govindasamy and Azariah, 1999;Gopinath et al., 2010;Prabakaran et al., 2020) but sometimes anthropogenic contamination (Barath Kumar et al., 2017;Lu and Kang, 2018;Sajimol et al., 2021). The physicochemical changes occurring in the overlying water column and within sediments remobilize the trace metals (Förstner, 1985;Chakraborty et al., 2015;Tiquio et al., 2017;Xie et al., 2019). After remobilization, various physicochemical and biological processes recycle the trace metals (Xu et al., 2017), which undergo bioaccumulation and biomagnification through a complex food web structure that initiates adverse health effects to aquatic organisms and humans (Gleyzes et al., 2002;Barath Kumar et al., 2017;Liang et al., 2018;Anandkumar et al., 2020). ...
Miri city has a dynamic coastal environment, mainly influenced by intensive sedimentation from the Baram River and excessive trace metal loading by the Miri River, which are significant environmental concerns. As the mobility, bioavailability, and toxicity of the trace metals in the sediments are largely controlled by their particulate speciation, the modified BCR sequential extraction protocol was applied to determine the particulate speciation of trace metals in the coastal sediments of Miri, to unravel the seasonal geochemical processes responsible for known observations, and to identify possible sources of these trace metals. The granulometric analysis results showed that littoral currents aided by the monsoonal winds have influenced the grain size distribution of the sediments, enabling us to divide the study area into north-east and south-west segments where the geochemical composition are distinct. The Cu (>84%) and Zn (82%) concentrations are predominantly associated with the exchangeable fraction, which is readily bioavailable. Pb and Cd are dominant in non-residual fractions and other metals viz., Fe, Mn, Co, Ni, and Cr are dominant in the residual fraction. Using Pearson's correlation and factor analysis, the major mechanisms controlling the chemistry of the sediments are identified as association of Cu and Zn with fine fraction sediments, sulphide oxidation in the Ssegment of the study area, atmospheric fallout of Pb and Cd in the river basins, precipitation of dissolved Fe and Mn supplied from the rivers and remobilization of Mn from the coastal sediments. Based on various pollution indices, it is inferred that the coastal sediments of NW Borneo are contaminated with Cu and Zn, and are largely bioavailable, which can be a threat to the local aquatic organisms, coral reefs, and coastal mangroves.
... All heavy metals have varying behaviours under different environmental conditions. Hence, it is necessary to determine the forms in which they are present to assess their toxicity in the sediment samples (Förstner, 1985). Cd, Mn and Mg were found to be primarily in the exchangeable (F1) form for all the sampling locations. ...
The present study has been conducted for three objectives for the assessment of sediment pollution loadings and their ecological risk. Firstly, the hierarchical clustering of the raw sediment dataset was carried out, which categorized the sampling locations into three statistically significant clusters, depending on their similarities in behaviours. Clusters 1, 2, and 3 corresponded to high, moderate, and low pollution sites, respectively. The principal component analysis was then carried out on the dataset for three different seasons; pre-monsoon, monsoon and post-monsoon respectively, which showed significant temporal changes in the pollution sources. Various indices such as contamination factor, pollution load index, enrichment factor, and the geo-accumulation index showed that the wetland is most affected in the post-monsoon season as compared to other seasons. At the same time, monsoon remains the best. This was attributed to the significant increase in the wetland’s water depth during the monsoon, coupled with the rise in precipitation capacity during the post-monsoon. Secondly, the potential ecological risk due to the contaminants displayed that the post-monsoon period has the greatest number of sites under the moderate risk category. In contrast, all the sites during the monsoon attributed to low risk. Also, Cd was found to be the primary contributor to ecological risk. Finally, chemical speciation analyses of all the heavy metals were conducted to determine their available forms in the sediment column. Cr, Mn, and Mg were observed to have a profoundly negative impact on aquatic ecology (available in F1 fraction in higher percentages). While Fe was predominant in reducible (F3) form, Cd was found to have equal contributions in reducible and oxidizable (F3 and F4, respectively) forms. Cu and Pb displayed typical complex characteristics of all the fractions in almost equal proportions. The results of the study indicated that although the anthropogenic interventions to the wetland have not been significant till yet, as far as the sediment contamination is concerned, it would be too late if swift and appropriate measures are not taken for restricting future probable contaminations.
... Adsorption and desorption process controls the mobility and bioavailability of metals in soil (Gedik et al., 2016). Organic matter, Fe and Al oxides, soil texture, pH and Oxidation-Redox Potential (ORP) are the most significant factors prevailing elements mobility and release into the overlying water column (Forstner, 1985;Chakraborty et al., 2015;Anandkumar et al., 2019). A metal, unlike other pollutants, are nonbiodegradable and can accumulate in soils and sediments over longer periods and enters into aquatic organisms via breathing and feeding and affect the top level predators including human (Gedik and Boran, 2013). ...
The accumulation and potential health risks of eight trace elements (Cu, Cd, Cr, Mn, Zn, Pb, Hg and As) were analyzed in the commercially important crayfish and oriental river prawn species from the Zhenjiang City, Jiangsu Province, China. The accumulation sequence of elements in different tissues were as gill > walking leg > muscle. Among the analyzed elements, majority of the elements were accumulated in the gill tissue, while Hg was concentrated in abdominal muscle and Zn in walking leg tissues. The elements Zn (95.9 μg g⁻¹) and Cd (0.02 μg g⁻¹) were the most and the least accumulated elements in the abdominal muscle tissue. The calculated estimated daily intake (EDI) and hazard indices (HI) of the analyzed elements in the tissue organs of Procambarus clarkii and Macrobrachium nipponense species were lower than the Chinese Food Health Criterion and international guideline values and results in no acute toxicities and thus, safe for human consumption. This study also suggests that Procambarus clarkii species can be used as an effective bio-indicator organism for examining the toxic heavy metals in the freshwater ecosystems.
... Mining is one of the most important sources of toxic metals into the environment and mine tailing disposal may result in acid mine drainage and the release of metals of toxic levels that impact on human health and the environment (Davies and Rice, 2001). Many studies such as Forstner (1985), Giller et al. (1988), Kozak (1991) and Grzebisz et al. (2002) have shown that metals are extremely persistent in the environment, non-biodegradable and readily accumulate to toxic levels. Contamination of soil is a constant danger due to pollution by toxic metals resulting in the infertility and unsuitability of the soil for plant growth and thus affecting the organisms in the food web (Marques et al. (2011). ...
Geo-accumulation index, enrichment factor, contamination factor and pollution load indexes were employed to evaluate Pb, Zn, As, Cd and Cr in soils near New Union mine dump. Arsenic and Cd were graded as unpolluted to moderately polluted whilst, Pb, Zn and Cr indicated no contamination (Igeo ≤0) in the soil. The EF values for Pb, Zn and Cr where attributed natural processes with no evidence of anthropogenic source. Meanwhile, As and Cd showed significant contamination in soil with CF>4. The PLI values for 95% of the sample sites were ≥1.5, which consequently indicated deterioration of soil quality.
Background
The environment is always subjected to exposure from different natural and anthropogenic sources of trace elements. The excessive intake of these trace elements may become toxic and cause health disorders to the people when the concentration exceeds certain threshold limits. The measurement of trace elements concentration in general and toxic trace elements concentration in particular is important for the assessment and prediction of risk to the environment and public. Distribution of trace elements in various environmental matrices depends on the nature of the element itself and the site-specific characteristics such as type of the matrices and its physicochemical parameters. In view of these aspects, an attempt is made to assess the concentration of trace elements and pollution indices in the sediment samples collected from the coastal belt of Kerala and possible conclusions were drawn.
Results
The results of pollution indices clearly indicate the moderate level of trace elements contamination in the coastal belts of Kerala. Significant correlations were observed between the concentration of trace elements and physicochemical parameters of the sediments.
Conclusion
Most of the trace elements enrichment in the coastal belt is due the crustal materials or natural weathering process and atmospheric deposition. The investigation revealed the sources of most of the elements present in the coastal belt of Kerala are lithogenic such as weathering and atmospheric deposition.
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