Effects of dibromoacetonitrile on rats following 13-week drinking water exposure

Urinary haloacetic acid concentrations in relation to sex and thyroid hormones among reproductive-aged men

Sex and thyroid hormones are critical for male reproductive health. However, the associations between haloacetic acid (HAA) exposure - a known endocrine disruptor - and sex and thyroid hormones in humans remains unclear. We thus recruited 502 male participants seeking fertility evaluation from a reproductive center. We measured concentrations of sex and thyroid hormones in a single blood sample and dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in repeated urine samples. Multivariable linear regression models were constructed to evaluate the associations between HAA concentrations and hormone measurements. After adjusting for potential confounders and urinary creatinine concentrations, urinary concentrations of TCAA were inversely associated with serum levels of sex hormone-binding globulin (SHBG), testosterone (T), T/luteinizing hormone ratio (T/LH), and thyroid stimulating hormone (TSH) (all P for trend < 0.10). Compared with participants in the lowest quartile of TCAA concentrations, those in the highest quartile had reduced serum levels of SHGB by 14.2 % (95% CI: -26.7, -3.0 %), T by 11.1 % (95% CI: -21.7, -1.3 %), T/LH by 21.0 % (95% CI: -36.7, -7.1 %), and TSH by 19.1 % (95% CI: -39.7, -1.5 %). Additionally, we observed inverse associations between continuous measurements of urinary HAAs and serum levels of free T, bioactive T, and estradiol. Our findings suggest that male HAA exposure may be associated with disrupted sex and thyroid function.

Protective role of electrophile-reactive glutathione for DNA damage repair inhibitory effect of dibromoacetonitrile

Dibromoacetonitrile (DBAN) is a disinfection byproduct (DBP) and linked with cancer in rodents, but the mechanism of its carcinogenicity has not been fully elucidated. We recently reported that DBAN induced inhibition of nucleotide excision repair (NER). In this study, we investigated if glutathione (GSH) is involved in the DBAN-induced inhibition of NER. Human keratinocytes HaCaT were pretreated with L-buthionine-(S,R)-sulfoximine (BSO) to deplete intracellular GSH. BSO treatment markedly potentiated the DBAN-induced NER inhibition as well as intracellular oxidation. The recruitment of NER proteins (transcription factor IIH, and xeroderma pigmentosum complementation group G) to DNA damage sites was inhibited by DBAN, which was further exacerbated by BSO treatment. Our results suggest that intracellular GSH protects cells from DBAN-induced genotoxicity including inhibition of DNA damage repair.

Identification of endocrine active disinfection by-products (DBPs) that bind to the androgen receptor

The formation of disinfection by-products (DBPs) in drinking water occurs when chemical disinfectants such as chlorine and chloramine react with natural organic matter and anthropogenic pollutants. Some DBPs have been linked to bladder cancer and infertility; however, the underlying mechanism of action is unknown. One possibility is disruption of the endocrine system, with DBPs binding to the androgen receptor and subsequently altering gene expression. Using the androgen receptor-binding assay and in silico molecular docking, the binding affinity of 21 suspected and known DBPs were tested individually at concentrations over the range 0.1 nM-2 mM. 14 DBPs were found to bind at IC₅₀ values ranging from 1.86 mM for 2,3-dichloropropionamide to 13.5 μM for 3,4,5,6-tetrachloro-benzoquinone as compared to the positive control, 4-n-nonylphenol which bound at 31.6 μM. Since DBPs are present in drinking waters as mixtures, the question of how IC₅₀ values for individual DBPs might be affected by the presence of other chemicals is addressed. Seven of the chemicals with the strongest binding affinities and one chemical with no binding affinity were tested in binary mixtures with 4-n-nonylphenol, a known androgenic chemical found in some surface waters. In these binary mixtures, concentration additive binding was observed. While typical levels of individual androgenic DBPs in drinking water are below their measured IC₅₀ values, their combined binding abilities in mixtures could be a source of androgen disruption.

The drinking water contaminant dibromoacetonitrile delays G1-S transition and suppresses Chk1 activation at broken replication forks

Chlorination of drinking water protects humans from water-born pathogens, but it also produces low concentrations of dibromoacetonitrile (DBAN), a common disinfectant by-product found in many water supply systems. DBAN is not mutagenic but causes DNA breaks and elevates sister chromatid exchange in mammalian cells. The WHO issued guidelines for DBAN after it was linked with cancer of the liver and stomach in rodents. How this haloacetonitrile promotes malignant cell transformation is unknown. Using fission yeast as a model, we report here that DBAN delays G1-S transition. DBAN does not hinder ongoing DNA replication, but specifically blocks the serine 345 phosphorylation of the DNA damage checkpoint kinase Chk1 by Rad3 (ATR) at broken replication forks. DBAN is particularly damaging for cells with defects in the lagging-strand DNA polymerase delta. This sensitivity can be explained by the dependency of pol delta mutants on Chk1 activation for survival. We conclude that DBAN targets a process or protein that acts at the start of S phase and is required for Chk1 phosphorylation. Taken together, DBAN may precipitate cancer by perturbing S phase and by blocking the Chk1-dependent response to replication fork damage.

Metabolomics evaluation of the in vivo toxicity of bromoacetonitriles: One class of high-risk nitrogenous disinfection byproducts

Bromoacetonitriles (BANs), one class of nitrogenous disinfection byproducts (N-DBPs), have frequently been detected in drinking water. The cytotoxicity and genotoxicity of BANs have been demonstrated in mammalian cells. However, a systematic study of the in vivo toxicity of BANs is rare. In this study, metabolomics combined with histopathology and oxidative stress analysis were used to evaluate the toxicity of BANs in mice. The results indicated that BAN exposure induced liver and kidney injury in mice. Furthermore, the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities decreased, and the level of malonaldehyde (MDA) increased in mice livers due to BANs exposure, which indicated that hepatic oxidative stress was induced. These toxicities increased with an increasing number of bromine at the α carbon. In addition, BAN exposure disrupted the metabolic pathways of amino acid, energy and lipid metabolism in mice. Our results provide evidence for the comprehensive omics endpoints of the in vivo toxicity of BANs.

Multibiomarker responses upon exposure to tetrabromobisphenol A in the freshwater fish Carassius auratus

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant. It has been released into aquatic environments, where it is toxic to aquatic organisms. In the present study, five enzymes, glutathione-S-transferase (GST), aspartate aminotransferase (AST), alanine aminotransferase (ALT), UDP-glucuronosyltransferase (UDPGT), and the antioxidant enzyme glutathione reductase (GR) in serum and liver of crucian carp (Carassius auratus) were selected for screening. These enzymes may be suitable for use as early warning indicators of chronic TBBPA exposure. UDPGT, AST, ALT, and GR activities in serum were found to be as more sensitive to TBBPA as those of the liver. When the concentration of TBBPA exceeded 0.50-0.71 mg/L for an exposure period of 32 days, GST, AST, ALT, and UDPGT activities cannot be restored to normal levels, suggesting that fish exposed to TBBPA above this threshold may incur irreversible damage. The activities of AST, ALT, and GR increased more significantly than GST and UDPGT at the lowest concentration of 0.35 mg/L. AST showed the strongest activity with respect to toxic kinetics, followed by ALT and GR. This remained true from day 4 of exposure to TBBPA to day 32. However, GR showed the clearest and most significant dose-effect relationship. This shows that each of these three enzymes can be used as a biomarker for early warning applications focusing on TBBPA pollution. AST and ALT are suitable for use in conventional monitoring of water quality in areas at risk for TBBPA pollution, and GR is more suitable for use in burst TBBPA pollution accidents where GR activity in fish would change with the TBBPA concentration of the flowing water.

Potential carcinogenic hazards of non-regulated disinfection by-products: haloquinones, halo-cyclopentene and cyclohexene derivatives, N-halamines, halonitriles, and heterocyclic amines

Drinking water disinfectants react with natural organic material (NOM) present in source waters used for drinking water to produce a wide variety of by-products. Several hundred disinfections by-products (DBPs) have been identified, but none have been identified with sufficient carcinogenic potency to account for the cancer risks projected from epidemiological studies. In a search for DBPs that might fill this risk gap, the present study projected reactions of chlorine and chloramine that could occur with substructures present in NOM to produce novel by-products. A review of toxicological data on related compounds, supplemented by use of a quantitative structure toxicity relationship (QSTR) program TOPKAT®) identified chemicals with a high probability of being chronically toxic and/or carcinogenic among 489 established and novel DBPs. Classes of DBPs that were specifically examined were haloquinones (HQs), related halo-cyclopentene and cyclohexene (HCP&H) derivatives, halonitriles (HNs), organic N-chloramines (NCls), haloacetamides (HAMs), and nitrosamines (NAs). A review of toxicological data available for quinones suggested that HQs and HCP&H derivatives appeared likely to be of health concern and were predicted to have chronic lowest observed adverse effect levels (LOAELs) in the low μg/kg day range. Several HQs were predicted to be carcinogenic. Some have now been identified in drinking water. The broader class of HNs was explored by considering current toxicological data on haloacetonitriles and extending this to halopropionitriles. 2,2-dichloropropionitrile has been identified in drinking water at low concentrations, as well as the more widely recognized haloacetonitriles. The occurrence of HAMs has been previously documented. The very limited toxicological data on HAMs suggests that this class would have toxicological potencies similar to the dihaloacetic acids. Organic N-halamines are also known to be produced in drinking water treatment and have biological properties of concern, but no member has ever been characterized toxicologically beyond bacterial or in vitro studies of genotoxicity. The documented formation of several nitrosamines from secondary amines from both natural and industrial sources prompted exploration of the formation of additional nitrosamines. N-diphenylnitrosamine was identified in drinking waters. Of more interest, however, was the formation of phenazine (and subsequently N-chorophenazine) in a competing reaction. These are the first heterocyclic amines that have been identified as chlorination by-products. Consideration of the amounts detected of members of these by-product classes and their probable toxicological potency suggest a prioritization for obtaining more detailed toxicological data of HQs>HCP&H derivatives>NCls>HNs. Based upon a ubiquitous occurrence and virtual lack of in vivo toxicological data, NCls are the most difficult group to assign a priority as potential carcinogenic risks. This analysis indicates that research on the general problem of DBPs requires a more systematic approach than has been pursued in the past. Utilization of predictive chemical tools to guide further research can help bring resolution to the DBP issue by identifying likely DBPs with high toxicological potency.

Determinants of whether or not mixtures of disinfection by-products are similar

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.

Neurotoxicological evaluation of two disinfection by-products, bromodichloromethane and dibromoacetonitrile, in rats

The Safe Drinking Water Act requires that the U.S. EPA consider noncancer endpoints for the assessment of adverse human health effects of disinfection by-products (DBPs). As an extension of our studies in which we demonstrated neurotoxicity at relatively low levels of dibromo- and dichloroacetic acids, we examined the potential neurotoxicity of other classes of DBPs. Bromodichloromethane (BDCM) and dibromoacetonitrile (DBAN) were administered to male and female F-344 rats via drinking water for 6 months. During exposure, rats were tested for neurobehavioral effects using a functional observational battery and motor activity, followed by perfusion fixation for neuropathological evaluation at the end of exposure. Calculating for chemical loss, fluid consumption, and body weight, average intakes were approximately: 9, 27, and 72mg/(kgday) BDCM, and 5, 12, and 29mg/(kgday) DBAN. Fluid consumption was decreased in most treatment groups, but body weight gain was altered only at the high concentrations. There were few neurobehavioral changes, and these were not considered toxicologically relevant. Of the general observations, there was only minimally decreased body tone in DBAN-treated high-dose males. Treatment-related neuropathological findings were not observed. Lowered fluid consumption was the most sensitive and consistent endpoint in the present studies. Thus, unlike the haloacetic acids, neurotoxicity may not be a concern for toxicity of halomethanes or haloacetonitriles.