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Correlations of Water Quality Parameters with Mutagenicity of Chlorinated Drinking Water Samples
Abstract
Adverse health effects that may result from chronic exposure to mixtures of disinfection by-products (DBPs) present in drinking waters may be linked to both the types and concentrations of DBPs present. Depending on the characteristics of the source water and treatment processes used, both types and concentrations of DBPs found in drinking waters vary substantially. The composition of a drinking-water mixture also may change during distribution. This study evaluated the relationships between mutagenicity, using the Ames assay, and water quality parameters. The study included information on treatment, mutagenicity data, and water quality data for source waters, finished waters, and distribution samples collected from five full-scale drinking water treatment plants, which used chlorine exclusively for disinfection. Four of the plants used surface water sources and the fifth plant used groundwater. Correlations between mutagenicity and water quality parameters are presented. The highest correlation was observed between mutagenicity and the total organic halide concentrations in the treated samples.
... Chlorine as a strong oxidant can react with the natural organic matters (NOM), anthropogenic contaminants and bromide/iodide in raw water leading to the formation of a wide variety of toxic DBPs, such as 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone together with several other chlorinated hydroxy furanones accounting for up to 76% of the observed drinking water genotoxicity (Nissinen et al., 2002;Myllykangas et al., 2003;Richardson et al., 2007). Drinking water genotoxicity was reported to increase with increasing the total organic carbon (TOC) concentration and correlate with the total organic halide and haloacetic acid (HAAs) concentrations in the treated waters, but has no obviously relationship with the concentrations of total trihalomethanes (THMs) (Schenck et al., 2009;Takanashi et al., 2009). The formation of the genotoxins including genotoxic DBPs may present the changes of the DOM characters, such as the organic composition and molecular weight, in water samples during the purification processes. ...
... This result indicated that brominated THMs played a more important role in finished water genotoxicity than brominated HAAs. It was different from the former report (Schenck et al., 2009). All of these findings warned us that although it was difficult to forecast the genotoxicity of drinking water from the water quality parameters because of the variability of drinking water mixtures in connection with the characteristics of the source water and the treatment processes, some water quality parameters could provide useful information for the research of drinking water genotoxicity. ...
... For the toxicity tests, the organic compounds in the water samples were extracted by adsorption on XAD resins according to the method described by Schenck et al. (Schenck et al. 2009). The resins (XAD-2 and XAD-8) were conditioned with acetone, methanol, and n-hexane in a Soxhlet extractor for > 8 h before extraction. ...
Drinking water safety is threatened by numerous toxic organic pollutants difficult to chemically monitor. This study aimed to determine the toxicological profiles of organic extracts (OEs) of water samples from source to tap in two drinking water supply systems in a metropolitan city, Central China, during different hydrological periods. Mortality, DNA damage, growth, and development of Caenorhabditis elegans were evaluated following exposure to OEs. The median lethal doses of OEs of drinking water samples (n = 48) ranged from 266 REF (relative enrichment factor) to > 1563 REF. When tested at a dose of 100 REF, 56.25% (27/48) of OEs induced genotoxicity, 4.17% (2/48) inhibited the growth, and 45.83% (22/48) decreased the offspring number in C. elegans. No clear temporal-spatial variation patterns of the OEs toxicity indicators were observed. The correlations among the toxicity indicators were generally poor. The observed toxicities were not closely related to the level of dissolved organic carbon in drinking water. These findings support using multiple endpoint bioassays, such as C. elegans-based approaches, as complementary tools to conventional chemical analysis for drinking water quality monitoring.
... Over the last two decades, water quality problems pertaining to NPS pollution have also been dealt effectively by using correlation analysis. The water quality can be assessed by developing empherical relationships among physicochemical parameters of the river with external factors such as land-use and land cover characteristics, cropping pattern, climatic changes, runoff risk etc. (Schenck et al., 2009;Pandey and Singh, 2017). have developed a scenario-based impact assessment model for river Ganges by coupling multivariate regression analysis with fuzzy decision-making approach. ...
Assessing the impact of land use cover on the river water quality is a pre-requisite to sustainable river basin planning and management. In recent times, non-point source pollution generated from agricultural watersheds has been significantly deteriorating water quality of major rivers such as river Ganges in India as described in this case study. The present work develops a Geographical Information System based mechanism to model non-point source pollution using multivariate regression analysis. The watershed model delineates runoff direction and identifies its lowest elevation points (outlets) near the river body where maximum pollution is caused by non-point source pollution, and thus provides a concrete evidence that agricultural runoff is the primary cause of increasing concentration of nitrogen and phosphorus compounds in the river. A case study of river Ganges basin, India is considered to demonstrate the applicability of the model. Relationships among six land cover and eleven critical water quality parameters are studied using multivariate regression near three selected sampling stations obtained using geographical information systems model. The results indicate that inorganic farming practices have a direct impact on the river water quality, leading to positive correlation (R2 ≥ 0.65) amongst ‘double-crop cover’ and ‘build-up area’ with Temperature, nitrogen as nitrite, nitrogen as nitrate, nitrite + nitrate, phosphorous as orthophosphate within the river body. Trend analysis study of temperature using Mann-Kendall test and Sen slope reveals an average of 0.23 °C/year positive trend in river temperature due to discharge of NPS pollution through agricultural watersheds. The study alarms the policymakers to educate the farmers to adopt best management practices such as increasing soil matter, usage of tile drainage, bioreactors, nutrient removal wetlands, using cover crops, etc. not only to increase crop productivity, but also to enhance the water quality in the riverine ecosystem.
... Therefore, targeted analysis of select chemical constituents could be inadequate for determining similarity. In addition to examples that rely on chemical analysis alone, a few studies with environmental mixtures have also included in vitro biological data in the evaluation of similarity (Schenck et al., 2009;Grimm et al., 2016). In this manuscript, we explore sufficient similarity in terms of both chemical and biological-response similarity as applied to a complex botanical mixture: Ginkgo biloba extract (GBE). ...
Botanical dietary supplements are complex mixtures with numerous potential sources of variation along the supply chain from raw plant material to the market. Approaches for determining sufficient similarity (i.e., complex mixture read-across) may be required to extrapolate efficacy or safety data from a tested sample to other products containing the botanical ingredient(s) of interest. In this work, screening-level approaches for generating both chemical and biological-response profiles were used to evaluate the similarity of black cohosh (Actaea racemosa) and Echinacea purpurea samples to well-characterized National Toxicology Program (NTP) test articles. Data from non-targeted chemical analyses and gene expression of toxicologically-important hepatic receptor pathways (AhR, CAR, PXR, FXR, and PPARα) in primary human hepatocyte cultures were used to determine similarity through hierarchical clustering. Although there were differences in chemical profiles across black cohosh samples, these differences were not reflected in the biological-response profiles. These findings highlight the complexity of biological-response dynamics that may not be reflected in chemical composition profiles. Thus, biological-response data could be used as the primary basis for determining similarity among black cohosh samples. Samples of Echinacea purpurea displayed better correlation in similarity across chemical and biological-response measures. The general approaches described herein can be applied to complex mixtures with unidentified active constituents to determine when data from a tested mixture (e.g., NTP test article) can be used for hazard identification of sufficiently similar mixtures, with the knowledge of toxicological targets informing assay selection when possible.
... Therefore, targeted analysis of select chemical constituents could be inadequate for determining similarity. In addition to examples that rely on chemical analysis alone, a few studies with environmental mixtures have also included in vitro biological data in the evaluation of similarity (Schenck et al., 2009;Grimm et al., 2016). In this manuscript, we explore sufficient similarity in terms of both chemical and biological-response similarity as applied to a complex botanical mixture: Ginkgo biloba extract (GBE). ...
Botanical dietary supplements are complex mixtures that can be highly variable in composition and quality, making safety evaluation difficult. A key challenge is determining how diverse products in the marketplace relate to chemically and toxicologically characterized reference samples (i.e., how similar must a product be in order to be well-represented by the tested reference sample?). Ginkgo biloba extract (GBE) was used as a case study to develop and evaluate approaches for determining sufficient similarity. Multiple GBE extracts were evaluated for chemical and biological-response similarity. Chemical similarity was assessed using untargeted and targeted chemistry approaches. Biological similarity was evaluated using in vitro liver models and short-term rodent studies. Statistical and data visualization methods were then used to make decisions about the similarity of products to the reference sample. A majority of the 26 GBE samples tested (62%) were consistently determined to be sufficiently similar to the reference sample, while 27% were different from the reference GBE, and 12% were either similar or different depending on the method used. This case study demonstrated that approaches to evaluate sufficient similarity allow for critical evaluation of complex mixtures so that safety data from the tested reference can be applied to untested materials.
... Wei et al. (2010) reported correlations for total trihalomethanes, total haloacetic acids, total haloacetonitriles, total haloketones, chloral hydrate and chloropicrin; however, these correlations were moderate (<0.6) and are not wholly comparable in that these authors reported Pearson correlation coefficients. Schenck et al. (2009) reported correlations for total trihalomethane, six haloacetic acids (combined), mutagenicity (estimated by the Ames test), total organic carbon and total organic halide, with the highest correlation being observed between mutagenicity and total organic halide content (r = 0.95). Villanueva et al. (2012) reported Spearman correlations for trihalomethanes, haloacetic acids and MX, which were similar to our results. ...
Chronic consumption of water, which contains contaminants, may give rise to adverse health effects. The Madrid region, covered by the population-based multicase-control (MCC-Spain) study, includes two drinking water supply areas. The different sources of the water, coupled together with the possible differences in water management, mean that there may be differences in drinking water quality. In the context of the MCC study, our aims were to describe contaminant concentrations in tap water drawn from various sampling points distributed around the region, assess these concentrations by reference to guideline values and study possible differences between the two supply areas. Tap water samples were collected from 34 sampling points in 7 towns in the Madrid region (19–29 April 2010), and 23 contaminants (metals, nitrates, disinfection by-product and Mutagen X levels) were quantified. We undertook a descriptive analysis of the contaminant concentrations in the water and compared them between the two water supply areas (Wilcoxon test). We created maps representing the distribution of the concentrations observed at water sampling points and assessed the correlations (Spearman’s coefficient) between the different parameters measured. The concentrations of the contaminants were below guideline values. There were differences between the two supply areas in concentration of nitrates (p value = 0.0051) and certain disinfection by-products. While there were positive correlations (rho >0.70) among some disinfection by-products, no correlations were found in metals or nitrates. The differences in nitrate levels could be linked to differences in farming/industrial activities in the catchment areas and in disinfection by-products might be related to the existence of different treatment systems or bromine content in source waters.
... HAAs represent the second most prevalent group of DBPs (Richardson et al. 2008). Previous studies have reported that the genotoxicity of drinking water correlated with HAAs concentrations (Schenck et al. 2009) and suggested that HAAs should be regarded as primary factors for controlling cancer risk from exposure to DBPs in drinking water (Zhang and Li 2000). Five HAAs currently regulated in the USA include monochloroacetic acid (MCA), monobromoacetic acid (MBA), dichloroacetic acid (DCA), dibromoacetic acid (DBA), and trichloroacetic acid (TCA) (US Environmental Protection Agency 1998). ...
Plant-based bioassays have gained wide use among the toxicological and/or ecotoxicological assessment procedures because of their simplicity, sensitivity, low cost, and reliability. The present study describes the use of Vicia faba (V. faba) micronucleus (MN) test and V. faba comet assay in the evaluation of the genotoxic potential of disinfection by-products (DBPs) commonly found in chlorine-disinfected drinking water. Five haloacetic acids and three halogenated acetonitriles were chosen as representatives of DBPs in this study because they are of potentially great public health risk. Results of the MN test indicated that monochloroacetic acid (MCA), monobromoacetic acid (MBA), dichloroacetic acid (DCA), dibromoacetic acid (DBA), trichloroacetic acid (TCA), and trichloroacetonitrile (TCAN) caused a statistically significant increase in MN frequency in V. faba root tip cells. However, no genotoxic response was observed for dichloroacetonitrile (DCAN) and dibromoacetonitrile (DBAN). Results of the comet assay showed that all tested DBPs induced a statistically significant increase in genomic DNA damage to V. faba root tip cells. On considering the capacity to detect genomic damage of a different nature, we suggest that a combination of V. faba MN test and V. faba comet assay is a useful tool for the detection of genotoxic effects of DBPs. It is worthy of assessing the feasibility of using V. faba comet assay combined with V. faba MN test to screen for the genotoxic activity of chlorinated drinking water in future work.
... described the comprehensive chemical analyses of the treated drinking-water concentrates developed for these experiments.Claxton et al. (2008) evaluated Salmonella mutagenicityand Crosby et al. (2008) evaluated the gene expression in rat hepatocytes for these Four Lab Study concentrates.Rice et al. (2009) andBull et al. (2009) assessed the ability to compare the composition of DBP mixtures andSchenk et al. (2009) evaluated correlation of DBP mixture composition with Salmonella mutagenicity. ...
2014 marks the 40th anniversary of the seminal discovery by Johannes Rook, in 1974, that trihalomethanes (THMs) were formed by the chlorination of natural organic matter (NOM) in drinking water. Since this discovery, which revolutionized how we viewed drinking water safety and quality, hundreds of other classes of disinfection by-products (DBPs) have been discovered. The finding in 1976 by the US National Cancer Institute that chloroform, the dominant THM, was a rodent carcinogen spurred a large number of epidemiology and toxicology studies into chlorinated drinking water. In 1985, this cancer finding was shown to be wrong. We should now be asking: What do we know about the human health impacts of DBPs in drinking water? Bladder cancer has been the most consistent finding from epidemiologic studies in North America and Europe and the possibility that chlorinated drinking water contributes an increased risk of bladder cancer remains a viable hypothesis. Despite some recent improvements in exposure assessments to focus on inhalation and dermal exposures rather than ingestion, no causal agent with sufficient carcinogenic potency has been identified, nor has a mechanistic model been validated. Consequently, a sensible precautionary approach to managing DBPs remains the only viable option based on four decades of evidence.
... described the comprehensive chemical analyses of the treated drinking-water concentrates developed for these experiments.Claxton et al. (2008) evaluated Salmonella mutagenicityand Crosby et al. (2008) evaluated the gene expression in rat hepatocytes for these Four Lab Study concentrates.Rice et al. (2009) andBull et al. (2009) assessed the ability to compare the composition of DBP mixtures andSchenk et al. (2009) evaluated correlation of DBP mixture composition with Salmonella mutagenicity. ...
Exposure to chlorination disinfection by-products (CxDBPs) is prevalent in populations using chlorination-based methods to disinfect public water supplies. Multifaceted research has been directed for decades to identify, characterize, and understand the toxicology of these compounds, control and minimize their formation, and conduct epidemiologic studies related to exposure. Urinary bladder cancer has been the health risk most consistently associated with CxDBPs in epidemiologic studies. An international workshop was held to (1) discuss the qualitative strengths and limitations that inform the association between bladder cancer and CxDBPs in the context of possible causation, (2) identify knowledge gaps for this topic in relation to chlorine/chloramine-based disinfection practice(s) in the United States, and (3) assess the evidence for informing risk management. Epidemiological evidence linking exposures to CxDBPs in drinking water to human bladder cancer risk provides insight into causality. However, because of imprecise, inaccurate, or incomplete estimation of CxDBPs levels in epidemiologic studies, translation from hazard identification directly to risk management and regulatory policy for CxDBPs can be challenging. Quantitative risk estimates derived from toxicological risk assessment for CxDBPs currently cannot be reconciled with those from epidemiologic studies, notwithstanding the complexities involved, making regulatory interpretation difficult. Evidence presented here has both strengths and limitations that require additional studies to resolve and improve the understanding of exposure response relationships. Replication of epidemiologic findings in independent populations with further elaboration of exposure assessment is needed to strengthen the knowledge base needed to better inform effective regulatory approaches.
... TOC is an indicator of the mass of organic matter, whereas UV 254 accounts for the specific structure and functional groups 48,49 . Schenck et al. (2009) reported that chlorinated drinking water in a test with TA100 without S9 correlated well with TOC, with the correlation coefficient between finished water and the total organic halogen content being the highest, approximately 0.95 50 , which is in agreement with our results. The total nitrogen content of the water correlated well with the mutagenicity, whereas ammonia nitrogen was not correlated; thus, we can deduce that nitrate nitrogen plays a major role in mutagenicity, which is in agreement with a previous study 5,51 . ...
A total of 54 water samples were collected during three different hydrologic periods (level period, wet period, and dry period) from Plant A and Plant B (a source for Yangtze River and Hanshui River water, respectively), and several water parameters, such as chemical oxygen demand (COD), turbidity, and total organic carbon (TOC), were simultaneously analyzed. The mutagenicity of the water samples was evaluated using the Ames test with Salmonella typhimurium strains TA98 and TA100. According to the results, the organic compounds in the water were largely frame-shift mutagens, as positive results were found for most of the tests using TA98. All of the finished water samples exhibited stronger mutagenicity than the relative raw and distribution water samples, with water samples collected from Plant B presenting stronger mutagenic strength than those from Plant A. The finished water samples from Plant A displayed a seasonal-dependent variation. Water parameters including COD (r = 0.599, P = 0.009), TOC (r = 0.681, P = 0.02), UV254 (r = 0.711, P = 0.001), and total nitrogen (r = 0.570, P = 0.014) exhibited good correlations with mutagenicity (TA98), at 2.0 L/plate, which bolsters the argument of the importance of using mutagenicity as a new parameter to assess the quality of drinking water.
... Similarly, a sharp rise in the activities of serum transaminases (aspartate aminotransferase (AST) and ALT), albumin, lactate dehydrogenase (LDH) and bilirubin in the birds that have been given a single dose of aflatoxin is indicative of an acute liver injury and kidney damage (Friedwald, Levy & Fredickson 1997). Studies have suggested an association between chlorination disinfection by-products and congenital anomalies, induction of oxidative stress, apoptosis and mutagenicity (Nieuwenhuijsen et al. 2009;Schenck et al. 2009). However, other studies have failed to establish an association between cancers or miscarriage and exposure to chlorinated drinking water (Sharma & Goel 2007;Goel 2008). ...
This study was designed to investigate the effects of prolonged oral administration of calcium hypochlorite in the drinking water of commercial cockerels. It was carried out in order to ascertain probable toxicity associated with prolonged exposure to calcium hypochlorite. Thirty-two healthy birds were used; they were grouped into four groups of eight. Group 1, which served as the control, received 10 mL/kg body weight of physiological saline. Groups 2, 3 and 4 received 0.0375 g, 0.375 g and 0.75 g of calcium hypochlorite per 10 litres of drinking water for six weeks respectively. Six weeks after the administration of calcium hypochlorite, blood was collected from the jugular vein to assess liver function, lipid profiles and for markers of oxidative stress. The results revealed a significant (p < 0.05) increase in alanine aminotransferase activity in a dose-dependent manner when compared with the control. Also, there was a significant (p < 0.05) increase in aspartate aminotransferase and alkaline phosphatase activity. Similarly, there was a significant (p < 0.05) increase in total cholesterol, triglycerides, high-density lipoprotein and low-density lipoprotein levels compared with the control. There was a significant increase in malondialdehyde and hydrogen peroxide generation with a concomitant significant (p < 0.05) decrease in serum glutathione level in a dose-dependent manner when compared with the control. In this study, calcium hypochloriteinduced hepatic damage via oxidative stress and decrease in antioxidant defense system was found. Therefore, prolonged exposure of chickens to calcium hypochlorite is potentially harmful.
... Correlations between mutagenicity and water quality parameters are presented. The highest correlation was observed between mutagenicity and the total organic halide concentrations in treated samples [6]. Since bromide serves as a precursor in some of the organic by-products, which are brominated, and probably affects the formation of some of the non-halogenated by-products, it is important to understand its effect upon the formation of these by-products. ...
The effects of pH and bromide ion concentration on the formation of nine haloacetic acids (HAAs) and total organic halogens (TOX) in chlorinated drinking water have been evaluated. In an extensive study, the relationships of nine HAAs with TOX have been investigated. Honesty Significant Differences test (HSD) and ANOVA tests were used for the statistical analyses. The study determined the concentration range of nine HAAs as of a percentage of TOX at varying experimental conditions. Statistical analyses showed that the parameters pH and Br had significant effects on the formation of nine HAAs and TOX. This study also showed that brominated and mixed species of HAAs would be dominant in the presence of high bromide ion concentration which contributes a high percentage of the TOX. The results of this study could be used to set up a maximum contaminant level of TOX as a water quality standard for chlorination by-products.
... Although some studies have been conducted on water samples that were assumed to contain mixtures of some water disinfection by-products, they were limited as for the definition of the composition of those mixtures and the toxic end points studied. Using Ames assay, a high correlation between mutagenicity and total organic halide concentrations was found in water samples collected from different drinking water treatment plants that used surface water from different locations [19]. Cytotoxicity and gene expression were found to be altered in cultured hepatocytes exposed to various dilutions of concentrates of chlorinated or ozonated/postchlorinated water that was originally collected from the Ohio River [20]. ...
In this study, groups of B6C3F1 male mice were treated with dichloroacetate (DCA), trichloroacetate (TCA), and mixtures of the compounds (Mix I, II, and III) daily by gavage, for 13 weeks. The tested doses were 7.5, 15, and 30 mg DCA/kg/day and 12.5, 25, and 50 mg TCA/kg/day. The DCA: TCA ratios in Mix I, II, and III were 7.5:12.5, 15:25, and 30:50 mg/kg/day, respectively. Peritoneal lavage cells were collected at the end of the treatment period and assayed for the biomarkers of phagocytic activation, including superoxide anion and tumor necrosis factor-alpha production, and myeloperoxidase activity. The mixtures produced nonlinear effects on the biomarkers of phagocytic activation, with Mix I and II effects were found to be additive, but Mix III effects were found to be less than additive.
... However, results are not completely comparable to ours since Wei et al. (2010) reported Pearson correlation coefficients. Correlations among total trihalomethanes, 6 haloacetic acids (combined), mutagenicity (estimated by the Ames test), total organic carbon and total organic halogen were evaluated by Schenck et al. (2009). In 18 finished water samples from five different treatment plants, the highest correlation occurred between mutagenicity and the total organic halogen content (r¼0.95). ...
... humic and fulvic acids) in surface waters may react with disinfectants to produce volatile and non-volatile disinfection by-products (DBP) that are potentially harmful to human and aquatic organisms. In particular, it has been demonstrated that chlorination, the most widely used method for water disinfection, leads to the formation of DBP with mutagenic and/or carcinogenic activity (Sujbert et al., 2006; Umbuzeiro Gde et al., 2006; Schenck et al., 2009 ). Moreover, several epidemiological studies revealed a positive association between the use of chlorinated drinking water obtained from surface sources with the incidence of cancer (e.g. ...
... Many of these compounds are not identified, raising concerns about safety and health effects of water treatment methods (Richardson et al., & 2007. Schenck et al., (2009) demonstrated a dose dependent correlation between the mutagenicity and chlorination of the drinking water. The nature and concentrations of disinfection byproducts are mainly influenced by type of disinfectant used and also by the distribution time of the treated water (reviewed by Bull et al., 2009). ...
In May of 2006 we suddenly began to observe neural tube defects (NTDs) in embryos of untreated control mice. We hypothesized the mice were being exposed unknowingly to a teratogenic agent and investigated the cause. Our results suggested that NTDs were not resulting from bedding material, feed, strain, or source of the mice. Additionally, mice were negative for routine and comprehensive screens of pathogens. To further test whether the NTDs resulted from infectious or genetic cause localized to our facility, we obtained three strains of timed pregnant mice from commercial suppliers located in four different states. All strains and sources of mice arrived in our laboratory with NTDs, implying that commercially available mice were possibly exposed to a teratogen prior to purchase. Our investigation eventually concluded that exposure to tap water was causing the NTDs. The incidence of NTDs was greatest in purchased mice provided tap water and lowest in purchased mice provided distilled deionized water (DDI). Providing mice DDI water for two generations (F2-DDI) eliminated the NTDs. When F2-DDI mice were provided tap water from three different urban areas prior to breeding, their offspring again developed NTDs. Increased length of exposure to tap water significantly increased the incidence of NTDs. These results indicate that a contaminant in municipal tap water is likely causing NTDs in mice. The unknown teratogen appears to have a wide geographic distribution but has not yet been identified. Water analysis is currently underway to identify candidate contaminants that might be responsible for the malformations.
Chlorination is important to the safeness of recouped water; though it shows concern about disinfection by-products (DBPs) formation and its toxic effects. DBPs generation mostly specified by category of disinfectant utilized and naturally occurring organic matter present in the water pre and post disinfection. Plants are exposed to diverse stresses of environment across their lifespan. Reactive oxygen species (ROS) perform significant roles in preserving ordinary plant growth and enhancing their tolerance towards stress. This study is focused on the generation and elimination of ROS in apical meristematic growth and responses in Vigna radiata towards DBPs exposure. Phytotoxic and genotoxic effect of selected DBPs, TCAA (trichloroacetic acid), TCM (trichloromethane), TBM (tribromomethane) revealed concentration-dependent root length inhibition, germination index, vigour index, tolerance index, root/shoot ratio with higher EC50 value for TCM (6000 mg/L, 50.26 mM) over TCAA and TBM (1850 mg/L, 11.32 mM; 4000 mg/L, 15.83 mM). DNA laddering assay demonstrated DBP induced DNA damage to be concentration-dependent too. The concentration-dependent increase in the lipid peroxidation, H2O2 generation for each DBPs examined with highest oxidative stress for TCAA over TBM and TCM at fixed concentration illustrates that possible mechanism behind observed toxicity may be via ROS. Its regulation by antioxidative defense enzymes activities can be attributed to observed decline in these enzymes (catalase, ascorbate peroxidase, guaiacol peroxidase) activities with increasing concentration again where TCAA found more significantly affected than TBM and TCM over control. Results thus provide a useful understanding of the mechanism of DBP induced phytotoxicity and genotoxicity in V.radiata.
This chapter discusses whole mixture approaches to assessing the risks of potentially hazardous chemical mixtures in the environment within the context of the risk assessment paradigm. Here, “whole mixtures” represent the combination of chemicals in the exposure being assessed. For risk assessment purposes, the environmental mixtures considered as a whole mixture can range from complex mixtures, consisting of perhaps hundreds of component chemicals, to less complex whole mixtures, such as all of the members (i.e., components) of a defined class of compounds. Whole mixture approaches are preferred to component approaches in mixture risk assessments. Because of the variability of whole mixtures encountered in the environment and the paucity of health effect studies, including dose-response studies, conducted on whole mixtures, if toxicity data are not available for an environmental mixture, the risk assessment could be based on surrogate toxicity information obtained from testing a sufficiently similar mixture. Biostatistical approaches for evaluating whether mixtures are sufficiently similar are included here as potential approaches that may, with further evaluation, prove useful in regulatory risk assessment contexts. The chapter concludes with a discussion of future directions for whole mixture risk assessment research.
Consideration of cumulative risk is necessary to evaluate properly the safety of, and the risks associated with, combined exposures. These combined exposures (“mixtures”) commonly occur from exposure to: environmental contaminants in air, soil, and water; pharmaceuticals and dietary supplements; consumer and personal care products; food additives and residues; and nonchemical stressors (e.g., physical and psychosocial). Risk assessments of mixtures of chemicals are more complex than those of single chemicals for two major reasons: (1) in combining chemicals to estimate mixture risk, it is necessary to rely on multiple assumptions; and (2) the potential for pharmacokinetic and/or pharmacodynamic interactions among mixture components. Additional difficulties exist for complex environmental mixtures, which typically contain a large fraction of total mixture mass of unknown identity and toxicity. The influence of data type, quality and quantity on the risk assessment approach is illustrated. Guidance is provided on when whole mixture risk assessment approaches are possible and when component-based approaches are needed. Advantages and disadvantages of whole mixture risk assessment approaches are discussed, including concerns due to unknown mixture mass and the current status of sufficient similarity methodology. Component-based methods based on dose-addition represent the majority of chemical mixture risk assessments that have been conducted to date; both hazard index-based (Hazard Index, Target Organ Toxicity Hazard Index, Interaction-Weighted Hazard Index) and index chemical (Relative Potency Factor and Toxic Equivalency Factor) approaches are reviewed. There is recognition of the need to consider the cumulative effects of both chemical and nonchemical stressors, but standard methods with a history of use are not available.
Surveillance of drinking water quality is extremely important to human health, assuming greater relevance in hospital environments, especially to those individuals who are immunocompromised. This study is aimed to determine the effect of increasing free chlorine (Cl) concentration in a hospital water network in regard to water quality monitoring and microbial growth control, between 2010 and 2013 in Porto. The average of free Cl concentration in the period under analysis showed some heterogeneity per floor, varying between 0.84 and 1.25 mg/L. In addition, there was a rise in proportion of samples that exceeded WHO guidelines (free Cl ≥ 0.5 mg/L), particularly in the last two years of the same period. With respect to microbial analysis, 22.4% of the samples were positive for Legionella spp., 6.4% for Pseudomonas aeruginosa, 15% and 30.4% for aerobic plate counts at 36 and 22 ºC, respectively. The proportion of positive samples decreased throughout the period under analysis, in particular for Legionella spp. (41.7% in 2010 vs. non-detectable in 2013) and P. aeruginosa (10.8% in 2010 vs. 3.3% in 2013). These results are in accordance with the gradual rise in free Cl concentration (0.78 ± 0.94 mg/L in 2010 vs. 1.16 ± 0.51 mg/L in 2013). In conclusion, a suitable plan for drinking water quality was instituted which resulted in reducing microbiological growth in the waterwork network, improving public health protection. However, the detection of critical points associated with lower levels of free Cl were found on certain floors/points-of-use, requiring the need to improve the monitoring water treatment system and/or implementation of additional technologies.
Humans are exposed to chemicals through voluntary and involuntary actions; to natural and synthetic chemicals all day, every day. Single chemical risk assessments are complex in and of themselves, and the assessment of chemical mixtures exponentially increases the complexity for toxicologists, regulators, and the public. Chemicals produce effects in biological systems which may or may not be related to their toxicity; some effects may be adaptive or may not be a direct part of their mode or mechanism of toxic action. These terms are commonly used and may be distinguished based on the level of detail implied. Mode of action usually describes the effect of a toxicant at the cellular or organ level, while mechanism of action implies an understanding of the interaction of the toxicant at the molecular level. Chemicals can have the same mode of action, but act via different mechanisms. Components in a chemical mixture are characterized by mode and/or mechanism for the purpose of grouping, described later.
Activated carbon fiber bio-film curtain with dynamic auxiliary was used to simulate the polluted source water in situ restoration. The effects of different temperatures and initial ammonia nitrogen concentrations on the remediation were discussed. The results indicated that the middle temperature was advantageous to the microorganisms on the biodegradation of organic matter and ammonia nitrogen, and low temperature was more conducive to microbial phosphorus removal. At 35℃, the removal efficiencies of CODMn and NH3-N were the best, 90% and 94%, respectively, whereas the highest removal rate of TP could reach 54% at 15℃. Under the different ammonia nitrogen concentrations (1.27,1.68 and 2.54 mg/L),the removal efficiency of CODMn was good and stabilized at approximately 85%. With the increase of initial ammonia nitrogen concentrations, the removal efficiency of NH3-N and TP decreased gradually. The removal rate of NH3-N reduced from 96% to 92%, while the removal rate of TP reduced from 40% to 30%.
The National Institute of Environmental Health Sciences (NIEHS) organized a workshop called “Advancing Research on Mixtures. New Perspectives and Approaches for Predicting Adverse Human Health Effects” (also called the NIEHS Mixtures Workshop) that was held in Chapel Hill, North Carolina.
The goal of the NIEHS Mixtures Workshop was to identify and focus on key issues that presented challenges in mixtures research (for this workshop, "mixtures" included combined independent exposures). The NIEHS used the results from the workshop to inform the development of an intramural and extramural mixtures research strategy. The workshop also provided input to the scientific community for advancing mixtures research. The summary document presented information from plenary and breakout group sessions that communicated results of the workshop to the greater scientific community.
In chemical mixtures risk assessment, the use of dose-response data developed for one mixture to estimate risk posed by a second mixture depends on whether the two mixtures are sufficiently similar. While evaluations of similarity may be made using qualitative judgments, this article uses nonparametric statistical methods based on the “bootstrap” resampling technique to address the question of similarity among mixtures of chemical disinfectant by-products (DBP) in drinking water. The bootstrap resampling technique is a general-purpose, computer-intensive approach to statistical inference that substitutes empirical sampling for theoretically based parametric mathematical modeling. Nonparametric, bootstrap-based inference involves fewer assumptions than parametric normal theory based inference. The bootstrap procedure is appropriate, at least in an asymptotic sense, whether or not the parametric, distributional assumptions hold, even approximately. The statistical analysis procedures in this article are initially illustrated with data from 5 water treatment plants (Schenck et al., 200910.
Schenck , K. M. ,
Sivaganesan , M. and
Rice , G. E. 2009. Correlations of water quality parameters with mutagenicity of chlorinated drinking-water samples. J. Toxicol. Environ. Health A, 72: 461–467. [Taylor & Francis Online], [PubMed], [Web of Science ®]View all references), and then extended using data developed from a study of 35 drinking-water utilities (U.S. EPA/AMWA, 198913.
U.S. Environmental Protection Agency/Association of Metropolitan Water Agencies . 1989. Disinfection by-products in United States drinking waters. Final report, La Verne, CA: James M. Montgomery Consulting Engineers and the Metropolitan Water District of Southern California. View all references), which permits inclusion of a greater number of water constituents and increased structure in the statistical models.
For evaluation of the adverse health effects associated with exposures to complex chemical mixtures in the environment, the U.S. Environmental Protection Agency (EPA) (2000)16.
U.S. Environmental Protection Agency. 2000. Supplementary guidance for conducting health risk assessment of chemical mixtures. EPA/630/R-00/002. Washington, DC: U.S. Environmental Protection Agency, Risk Assessment Forum http://www.epa.gov/ncea/raf/pdfs/chem_mix/chem_ mix_08_2001.pdf View all references states, “if no data are available on the mixture of concern, but health effects data are available on a similar mixture … a decision must be made whether the mixture on which health effects are available is ‘sufficiently’ similar to the mixture of concern to permit a risk assessment.” This article provides a detailed discussion of statistical considerations for evaluation of the similarity of mixtures. Multivariate statistical procedures are suggested to determine whether individual samples of drinking-water disinfection by-products (DBPs) vary significantly from a group of samples that are considered to be similar. The application of principal components analysis to (1) reduce the dimensionality of the vectors of water samples and (2) permit visualization and statistical comparisons in lower dimensional space is suggested. Formal analysis of variance tests of homogeneity are illustrated. These multivariate statistical procedures are applied to a data set describing samples from multiple water treatment plants. Essential data required for carrying out sensitive analyses include (1) identification and measurement of toxicologically sensitive process input and output characteristics, and (2) estimates of variability within the data to construct statistically efficient estimates and tests.
Reactive chemicals have been used to disinfect drinking waters for over a century. In the 1970s, it was first observed that the reaction of these chemicals with the natural organic matter (NOM) in source waters results in the production of variable, complex mixtures of disinfection by-products (DBP). Because limited toxicological and epidemiological data are available to assess potential human health risks from complex DBP mixture exposures, methods are needed to determine when health effects data on a specific DBP mixture may be used as a surrogate for evaluating another environmental DBP mixture of interest. Before risk assessors attempt such efforts, a set of criteria needs to be in place to determine whether two or more DBP mixtures are similar in composition and toxicological potential. This study broadly characterizes the chemical and toxicological measures that may be used to evaluate similarities among DBP mixtures. Variables are discussed that affect qualitative and quantitative shifts in the types of DBP that are formed, including disinfectants used, their reactions with NOM and with bromide/iodide, pH, temperature, time, and changes in the water distribution system. The known toxicological activities of DBP mixtures and important single DBPs are also presented in light of their potential for producing similar toxicity. While DBP exposures are associated with a number of health effects, this study focuses on (1) mutagenic activity of DBP mixtures, (2) DBP cancer epidemiology, and (3) toxicology studies to evaluate similarity among DBP mixtures. Data suggest that further chemical characterization of DBP mixtures and more systematic study of DBP toxicology will improve the quality and usefulness of similarity criteria.
Humans are exposed daily to complex mixtures of environmental chemical contaminants, which arise as releases from sources such as engineering procedures, degradation processes, and emissions from mobile or stationary sources. When dose-response data are available for the actual environmental mixture to which individuals are exposed (i.e., the mixture of concern), these data provide the best information for dose-response assessment of the mixture. When suitable data on the mixture itself are not available, surrogate data might be used from a sufficiently similar mixture or a group of similar mixtures. Consequently, the determination of whether the mixture of concern is "sufficiently similar" to a tested mixture or a group of tested mixtures is central to the use of whole mixture methods. This article provides an overview for a series of companion articles whose purpose is to develop a set of biostatistical, chemical, and toxicological criteria and approaches for evaluating the similarity of drinking-water disinfection by-product (DBPs) complex mixtures. Together, the five articles in this series serve as a case study whose techniques will be relevant to assessing similarity for other classes of complex mixtures of environmental chemicals. Schenck et al. (2009) describe the chemistry and mutagenicity of a set of DBP mixtures concentrated from five different drinking-water treatment plants. Bull et al. (2009a, 2009b) describe how the variables that impact the formation of DBP affect the chemical composition and, subsequently, the expected toxicity of the mixture. Feder et al. (2009a, 2009b) evaluate the similarity of DBP mixture concentrates by applying two biostatistical approaches, principal components analysis, and a nonparametric "bootstrap" analysis. Important factors for determining sufficient similarity of DBP mixtures found in this research include disinfectant used; source water characteristics, including the concentrations of bromide and total organic carbon; concentrations and proportions of individual DBPs with known toxicity data on the same endpoint; magnitude of the unidentified fraction of total organic halides; similar toxicity outcomes for whole mixture testing (e.g., mutagenicity); and summary chemical measures such as total trihalomethanes, total haloacetic acids, total haloacetonitriles, and the levels of bromide incorporation in the DBP classes.
Recent epidemiological studies conducted in Finland have reported a positive correlation between the mutagenicity of chlorinated drinking waters and certain human cancers. In these studies, past exposure to drinking water mutagenicity was assessed using a model developed by Vartiainen et al. [1] based on data collected in Finland. In this model, mutagenicity, as determined in the Ames assay, is a function of the total organic carbon (TOC) concentration of the water, chlorine dose, and to a minor extent, the concentration of ammonia. A study has been initiated to assess the applicability of this model to source waters and water treatment practices in the United States. Water samples were collected from three full-scale treatment plants and one pilot-scale plant. All the plants used chlorine exclusively for disinfection. One full-scale plant used ground water. Surface water sources were used by the other plants. TOC and ammonia concentrations were determined analytically and chlorine doses were obtained from the treatment plants. The water samples were concentrated by XAD resin adsorption for testing in the Ames assay. The observed levels of mutagenicity in the finished waters were 1.5 to 2-fold higher than those predicted using the model as specified in Vartiainen et al. [1]. Consequently, further validation is needed prior to widespread use of the Finnish model to assess exposure to mutagenicity in chlorinated drinking waters in the United States.
Although disinfection was one of the major public health advances in the last century and continues to be so in the twenty-first century, the disinfectants themselves may react with naturally occurring materials in treated water to form unintended by-products, which may themselves pose risks. This is of particular concern with regard to the use of chlorine. Generation of disinfection by-products (DBPs) has been shown to be a function of various factors including total organic carbon concentration, type of organic precursor, chlori-nation level, pH, temperature, reaction time, and UV-254 absorbance. Another factor affecting DBP formation is the presence and concentration of the bromide ion in the raw or finished water. Bromine substitutes for chlorine to produce bromine-containing homologues of the more familiar chlorine species. The current list of by-products targeted for regulation contains brominated and mixed bromine-chlorine species of total trihalo-methanes and haloacetic acids. These are known to form in bromide-containing waters when chlorinated. To control chlorination DBPs therefore requires an understanding of the factors that influence their formation. This paper presents a model that can be used to predict the formation of chlorinated, brominated, and mixed species compounds based on initial chlorine concentration, chlorine consumption, bromide ion concentration, and pH. The model clearly shows that higher levels of bromide in the water favor the formation of brominated compounds. Brominated compounds also form faster than chlorinated compounds.
Although chemical disinfection of drinking water is a highly protective public health practice, the disinfection process is known to produce toxic contaminants. Epidemiological studies associate chlorinated drinking water with quantitatively increased risks of rectal, kidney, and bladder cancer. One study found a significant exposure-response association between water mutagenicity and relative risk for bladder and kidney cancer. A number of studies found that several types of disinfection processes increase the level of mutagens detected by the Salmonella assay. As part of a comprehensive study to examine chlorinated and ozonated/postchlorinated drinking water for toxicological contaminants, the Salmonella mutagenicity assay was used to screen both volatile and nonvolatile organic components. The assay also compared the use of reverse osmosis and XAD resin procedures for concentrating the nonvolatile components. Companion papers provide the results from other toxicological assays and chemical analysis of the drinking water samples. The volatile components of the ozonated/postchlorinated and chlorinated water samples and a trihalomethane mixture were mutagenic to a Salmonella tester strain transfected with a rat theta-class glutathione S-transferase and predominantly nonmutagenic in the control strain. In this study, the nonvolatile XAD concentrate of the untreated water possessed a low level of mutagenic activity. However, compared to the levels of mutagenicity in the finished water XAD concentrates, the contribution from the settled source water was minimal. The mutagenicity seen in the reverse osmosis concentrates was < 50% of that seen in the XAD concentrates. Overall, mutagenic responses were similar to those observed in other North American studies and provide evidence that the pilot plant produced disinfection by-products similar to that seen in other studies.
This article describes the disinfection by-product (DBP) characterization portion of a series of experiments designed for comprehensive chemical and toxicological evaluation of two drinking-water concentrates containing highly complex mixtures of DBPs. This project, called the Four Lab Study, involved the participation of scientists from four laboratories and centers of the U.S. Environmental Protection Agency (EPA) Office of Research and Development, along with collaborators from the water industry and academia, and addressed toxicologic effects of complex DBP mixtures, with an emphasis on reproductive and developmental effects that are associated with DBP exposures in epidemiologic studies. Complex mixtures of DBPs from two different disinfection schemes (chlorination and ozonation/postchlorination) were concentrated successfully, while maintaining a water matrix suitable for animal studies. An array of chlorinated/brominated/iodinated DBPs was created. The DBPs were relatively stable over the course of the animal experiments, and a significant portion of the halogenated DBPs formed in the drinking water was accounted for through a comprehensive qualitative and quantitative identification approach. DBPs quantified included priority DBPs that are not regulated but have been predicted to produce adverse health effects, as well as those currently regulated in the United States and those targeted during implementation of the Information Collection Rule. New by-products were also reported for the first time. These included previously undetected and unreported bromo- and chloroacids, iodinated compounds, bromo- and iodophenols, and bromoalkyltins.
Disinfection by-products (DBPs) are formed when disinfectants (chlorine, ozone, chlorine dioxide, or chloramines) react with naturally occurring organic matter, anthropogenic contaminants, bromide, and iodide during the production of drinking water. Here we review 30 years of research on the occurrence, genotoxicity, and carcinogenicity of 85 DBPs, 11 of which are currently regulated by the U.S., and 74 of which are considered emerging DBPs due to their moderate occurrence levels and/or toxicological properties. These 74 include halonitromethanes, iodo-acids and other unregulated halo-acids, iodo-trihalomethanes (THMs), and other unregulated halomethanes, halofuranones (MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] and brominated MX DBPs), haloamides, haloacetonitriles, tribromopyrrole, aldehydes, and N-nitrosodimethylamine (NDMA) and other nitrosamines. Alternative disinfection practices result in drinking water from which extracted organic material is less mutagenic than extracts of chlorinated water. However, the levels of many emerging DBPs are increased by alternative disinfectants (primarily ozone or chloramines) compared to chlorination, and many emerging DBPs are more genotoxic than some of the regulated DBPs. Our analysis identified three categories of DBPs of particular interest. Category 1 contains eight DBPs with some or all of the toxicologic characteristics of human carcinogens: four regulated (bromodichloromethane, dichloroacetic acid, dibromoacetic acid, and bromate) and four unregulated DBPs (formaldehyde, acetaldehyde, MX, and NDMA). Categories 2 and 3 contain 43 emerging DBPs that are present at moderate levels (sub- to low-mug/L): category 2 contains 29 of these that are genotoxic (including chloral hydrate and chloroacetaldehyde, which are also a rodent carcinogens); category 3 contains the remaining 14 for which little or no toxicological data are available. In general, the brominated DBPs are both more genotoxic and carcinogenic than are chlorinated compounds, and iodinated DBPs were the most genotoxic of all but have not been tested for carcinogenicity. There were toxicological data gaps for even some of the 11 regulated DBPs, as well as for most of the 74 emerging DBPs. A systematic assessment of DBPs for genotoxicity has been performed for approximately 60 DBPs for DNA damage in mammalian cells and 16 for mutagenicity in Salmonella. A recent epidemiologic study found that much of the risk for bladder cancer associated with drinking water was associated with three factors: THM levels, showering/bathing/swimming (i.e., dermal/inhalation exposure), and genotype (having the GSTT1-1 gene). This finding, along with mechanistic studies, highlights the emerging importance of dermal/inhalation exposure to the THMs, or possibly other DBPs, and the role of genotype for risk for drinking-water-associated bladder cancer. More than 50% of the total organic halogen (TOX) formed by chlorination and more than 50% of the assimilable organic carbon (AOC) formed by ozonation has not been identified chemically. The potential interactions among the 600 identified DBPs in the complex mixture of drinking water to which we are exposed by various routes is not reflected in any of the toxicology studies of individual DBPs. The categories of DBPs described here, the identified data gaps, and the emerging role of dermal/inhalation exposure provide guidance for drinking water and public health research.
The formation of mutagenic activity in drinking waters containing various amounts of organic matter was studied in Finland. It was found possible to model the mutagenicities of chlorinated drinking waters as a function of the total organic carbon (TOC), of the chlorine dose, and as a minor factor, of the amount of ammonia. The equation was the sum of the two chlorination steps, each of them of the same form: ,where c=[TOC] [Cl2]. Here [TOC] is the concentration of total organic carbon and [Cl2] the chlorine dose, in units of mg per liter; A and K are constants. The regression coefficient R for the measured mutagenicities in TA 100 and the modelled mutagenicities was 0.854 in 86 drinking water samples.Ozone or chlorine dioxide preoxidation combined with chlorine postdisinfection resulted in lower mutagenicities than if chlorine was used in both steps.The mutagenicities were slightly higher in winter than in summer.
On a monthly basis, over a one year period, disinfection by-products (DBPs) were measured in raw water and in treated water at four locations in the distribution system of three water treatment plants that applied different treatment processes. DBP levels fluctuated as a function of water treatment practice (and variations therein) and the age and temperature of the water. Trihalomethane levels were higher in the summer than in the winter and increased in the distribution system with increasing distance from the plant. Levels of haloacetic acids and other DBPs were usually higher in summer than in winter but their levels did not increase consistently within the distribution system. After an initial increase, levels of dichloro- and trichloroacetic acids often decreased within the distribution system. No single sampling event captured the complete image of the behaviour of DBPs in drinking water. The authors recommend that in-depth studies be carried out to develop sampling strategies for DBPs.
Concentrates of drinking water in Tokyo and the neighboring prefecture were tested with Ames assays. The correlation of mutagenesis with total organic halogen (TOX) indicated that TOX of 100 μ g/l was equivalent to 300 net rev./l with TA100.
An inventory on the presence of mutagenic activity (Ames test) in 18 cities (20 drinking water types) was carried out in The Netherlands. Fourteen drinking water types of twenty showed mutagenic activity in the Ames test in volumes varying from 0.5 to 3 litre. Classifying these cities to their water source it appeared that only three of the fifteen cities which prepare their drinking water from surface water or a mixture of surface and ground water, did not show mutagenic activity. Two of the five cities which use ground water as water source showed mutagenic activity although; in one city the activity was marginal. Correlating some chemical parameters in drinking water with mutagenic activity of organic drinking water concentrates revealed, that AOC1 showed the highest correlation with the direct mutagenic activity in strain TA 98 and TA 100. From these data concentration levels of chemical parameters were calculated above which a doubling of revertants may be expected.Finally it was also shown that a chlorine treatment applied during drinking water preparation correlated well with the direct mutagenic activity in strain TA 98 and TA 100.
Drinking water disinfection by-products (DBPs) are an unintended consequence of using chemical disinfectants to kill harmful pathogens in water. DBPs are formed by the reaction of disinfectants with naturally occurring organic matter, bromide, and iodide, as well as from anthropogenic pollutants. Potential health risks of DBPs from drinking water include bladder cancer, early-term miscarriage, and birth defects. Risks from swimming pool DBP exposures include asthma and other respiratory effects. Several DBPs, such as trihalomethanes (THMs), haloacetic acids (HAAs), bromide, and chlorite, are regulated in the U.S. and in other countries, but other “emerging” DBPs, such as iodo-acids, halonitromethanes, haloamides, halofuranones, and nitrosamines, are not widely regulated. DBPs have been reported for the four major disinfectants: chlorine, chloramines, ozone, and chlorine dioxide (and their combinations), as well as for newer disinfectants, such as UV treatment with post-chlorination. Each disinfectant can produce its own suite of by-products. Several classes of emerging DBPs are increased in formation with the use of alternative disinfectants (e.g., chloramines), including nitrogen-containing DBPs (“N-DBPs”), which are generally more genotoxic and cytotoxic than those without nitrogen. Humans are exposed to DBPs not only through ingestion (the common route studied), but also through other routes, including bathing, showering, and swimming. Inhalation and dermal exposures are now being recognized as important contributors to the overall human health risk of DBPs. Analytical methods continue to be developed to measure known DBPs, and research continues to uncover new highly polar and high-molecular-weight DBPs that are part of the missing fraction of DBPs not yet accounted for. New studies are now combining toxicology and chemistry to better understand the health risks of DBPs and uncover which are responsible for the human health effects.
Sample pH and the presence of a chlorine residual were evaluated for their effects of the recovery of mutagenicity in drinking water following concentration by XAD resins. The levels of mutagenicity in the pH 2 concentrates were 7-8-fold higher than those of the pH 8 concentrates, suggesting that acidic compounds accounted for the majority of the mutagenicity. The presence of a chlorine residual had little effect on the levels of mutagenicity at either pH. Comparisons of the mutagenic activity for the pH 2 resin concentrates vs. pH 8 concentrates prepared by lyophilization further indicated that the acidic mutagens were products of disinfection with chlorine and not artifacts of the sample acidification step in the concentration procedure. 27 references, 6 figures, 1 table.
A universal and novel strategy for the immobilization of polymers has been developed for studying the interaction between plasmid DNA and synthetic polymers with surface plasmon resonance spectrometry. The introduction of thiol moieties in polymers has been applied for a reliable determination of apparent kinetic rate constants between plasmid DNA and the nonviral carrier polymers. Thiolated poly(L-lysine) and poly[(2-dimethylamino)ethyl methacrylate] yielded reproducible sensor surfaces, contrary to the nonthiolated polymers. The knowledge of the kinetic parameters may play a crucial role in the development of nonviral carrier systems for gene therapy, because the dissociation rate constant is strongly correlated to the effectiveness of cell transfection.
Humic acid chlorination products are being studied in an effort to identify the chemicals responsible for the mutagenicity formed during water chlorination. In the present report, 19 chlorinated organic compounds have been identified and quantified in ether extracts of chlorinated humic acid solutions. 10 of these compounds, including a number of chlorinated propanones and chlorinated propenals, are direct-acting mutagens in the Salmonella/microsome mutagenicity assay. The position of the chlorine substituent has been found to be an important factor in the mutagenic activity of these two classes of compounds. The total mutagenicity of the compounds identified thus far, when tested either individually or as a composite, accounts for only 7-8% of the total TA100 mutagenicity, and less than 2% of the TA98 mutagenicity formed during humic acid chlorination. The addition of bromide to the humic acid chlorination reaction results in up to a 2-fold increase in the level of mutagenicity formed.
The organic extract from the drinking water of Kuopio, Eastern Finland, turned out to be highly mutagenic in the Ames test. The direct mutagenic activities of the acid/neutral fractions of 48 drinking water samples were on an average 1700 net revertants/l in strain TA100. The highest activities were more than 6000 net revertants/l, and one drinking water sample exceeded 10 000 net revertants/l. The drinking water of Kuopio is produced from lake water which has a relatively high content of humic substances. Water processing involved two chlorination phases. The organic constituents of the water samples were isolated either by continuous liquid-liquid extraction or by absorption on XAD 8 resin.
Five toxicological tests were performed using concentrated drinking water samples collected at a pilot-scale drinking water treatment plant that had streams treated with different disinfectants (no disinfectant, ozone, chlorine dioxide, monochloramine, or chlorine) before treatment with granular activated carbon (GAC). The toxicological tests used in this study were the Ames Salmonella assay, a subchronic in vivo toxicity assay in mice, the SENCAR mouse skin initiation-promotion assay, a rat liver foci assay, and the lung adenoma assay in strain A mice. These tests were conducted to determine the general toxicity and the mutagenic/carcinogenic potential associated with the use of disinfection and/or GAC in the treatment of drinking water. The stability of the mutagenic activity of the samples tested was determined by repeated analysis using the Ames Salmonella assay. Results indicated that the samples remained mutagenic for the duration of the tests. All the drinking water concentrates (4000 X) prepared by the XAD resin adsorption procedure failed to provide statistically significant indication of carcinogenic activity in the SENCAR mouse, rat liver foci, and the lung adenoma assays. However, concentrates of the chlorine, chlorine dioxide, and monochloramine treated waters gave consistent mutagenic responses in the Ames Salmonella assay. GAC was effective for 6 months in removing both the mutagenicity of chlorine-treated water and the potential of water to become mutagenic when treated with chlorine. In the in vivo, subchronic 30-day toxicity test in mice, some statistically significant differences in organ weights and body weights of animals exposed to different concentrates of some of the samples were observed. However, a consistent pattern of these differences indicating overt toxicity was not detected.
Aqueous chlorination of humic acids results in the formation of compounds with direct-acting mutagenic activity in the Ames/Salmonella plate assay for tester strains TA98, TA100, TA1535, TA1537 and TA1538. The addition of a rat-liver microsomal fraction (S9) plus cofactors causes a substantial decrease of activity, the extent of which is tester strain dependent. The non-chlorinated humic acids are not mutagenic either in the presence or absence of S9. Formation of mutagenic activity and of total organic halogen (TOX) is linearly related to humic concentration in the range of 0.2-1.6 mg/ml total organic carbon (TOC), and to chlorine concentration in the range of 0.1-1.0 chlorine equivalents per mole of carbon. The mutagenic activity is due predominantly to non-volatile compounds. Mutagenic activity is also detectable, after sample concentration by lyophilization, upon chlorination at a humic acid level of 0.02 mg/ml TOC. The specific mutagenic activities (per mg TOX), and also the degree of chlorine incorporation into humic acid, at 0.02 mg/ml TOC are similar to those present after chlorination at 1 mg/ml TOC. Production of mutagens is greatly dependent on the chlorination pH, with a pattern of decreasing mutagenic activity with increasing pH. This order of activity can be at least partially explained by the alkali liability of the compounds. Chlorination of commercial humic acids is proposed as a model for examination of mutagen formation during water chlorination.
The methods for detecting carcinogens and mutagens with the Salmonella mutagenicity test were described previously (Ames et al., 1975b). The present paper is a revision of the methods. Two new tester strains, a frameshift strain (TA97) and a strain carrying an ochre mutation on a multicopy plasmid (TA102), are added to the standard tester set. TA97 replaces TA1537. TA1535 and TA1538 are removed from the recommended set but can be retained at the option of the investigator. TA98 and TA100 are retained. We discuss other special purpose strains and present some minor changes in procedure, principally in the growth, storage, and preservation of the tester strains. Two substitutions are made in diagnostic mutagens to eliminate MNNG and 9-aminoacridine. Some test modifications are discussed.
A number of recent papers have suggested basing the statistical analysis of Salmonella (Ames) mutagenicity test results on a mathematical model of the complete dose-response curve. For most mutagens at low doses the curve increases linearly; then, as the dose increases, the curve may flatten and finally turn downwards due primarily to effects of toxicity. The exact mechanism underlying this shape is, however, not well understood and is likely to vary for different chemicals. A different approach is to assume that the initial part of the curve is linear and to base the statistical analysis solely on this region, reasoning that it contains most of the interpretable information about the mutagenesis dose response. In this paper a formal method of deciding which points are on the initial linear part of the curve is described, and a statistical method is proposed for analyzing these points. Computer simulations are used to examine the properties of the procedure and comparisons are made with a previously proposed mathematical model of the whole curve. It is concluded that the method suggested here provides a very satisfactory, robust method for the standard analysis of Salmonella data.
In concentrates of water produced in a laboratory simulation of a drinking water treatment process, direct-acting, nonvolatile
mutagens were readily detected by means of the Ames Salmonella test. The mutagens were shown to be produced by the chlorination
process. Treatment of the water with chloramine resulted in less mutagenic activity than treatment with free chlorine. Dechlorination
of drinking water with sulfite sharply reduced the mutagenic activity. Treatment with sulfur dioxide is proposed as an effective,
inexpensive method of reducing the direct-acting mutagenic activity of drinking water and of aqueous industrial effluents.
A call for analytical techniques to determine unidentified disinfection byproducts in drinking water.
Impact of biomass on the stability of haloacetic acids and trihalomethanes in a simulated distribution system
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Mutagenicity of drink-ing water samples before and after distribution Application of a Finnish mutagenicity model to drinking waters in the United States
- K M Schenck
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