Mutagenic analysis of six disinfection by-products in the Tk gene of mouse lymphoma cells.

Drinking water must be disinfected prior to its distribution for human consumption. This water treatment process generates disinfection by-products (DBPs), formed by the interaction of the disinfectant with organic matter, anthropogenic contaminants and inorganic (bromide/iodide) matter naturally present in source water. Due to the potential genotoxic/carcinogenic risk of these DBPs, we have investigated the mutagenic potential of six of such compounds on the thymidine kinase (Tk) gene in the well-validated mouse lymphoma assay (MLA). The MLA quantifies a wide range of genetic alterations affecting the expression of this gene in L5178Y/Tk(+/-)-3.7.2C cells. In this study we selected six emerging DBPs, corresponding to three different chemical classes: halonitromethanes (bromonitromethane and trichloronitromethane), halogenated acetaldehydes (tribromoacetaldehyde and chloral hydrate) and hydroxyfuranones (mucobromic and mucochloric acids), each class including one chlorinated and one brominated form. The results showed that after 4h of treatment, only mucobromic acid increased the frequency of mutant colonies, with a higher proportion of small colonies, which would indicate a clastogenic potential. This is the first study reporting mutagenicity data in mammalian cells for the six selected DBPs.

Genotoxic effects in swimmers exposed to disinfection by-products in indoor swimming pools.

BACKGROUND: Exposure to disinfection by-products (DBPs) in drinking water has been associated with cancer risk. A recent study (Villanueva et al. 2007; Am J Epidemiol 165:148-156) found an increased bladder cancer risk among subjects attending swimming pools relative to those not attending. OBJECTIVES: We evaluated adults who swam in chlorinated pools to determine whether exposure to DBPs in pool water is associated with biomarkers of genotoxicity. METHODS: We collected blood, urine, and exhaled air samples from 49 nonsmoking adult volunteers before and after they swam for 40 min in an indoor chlorinated pool. We estimated associations between the concentrations of four trihalomethanes (THMs) in exhaled breath and changes in micronuclei (MN) and DNA damage (comet assay) in peripheral blood lymphocytes before and 1 hr after swimming; urine mutagenicity (Ames assay) before and 2 hr after swimming; and MN in exfoliated urothelial cells before and 2 weeks after swimming. We also estimated associations and interactions with polymorphisms in genes related to DNA repair or to DBP metabolism. RESULTS: After swimming, the total concentration of the four THMs in exhaled breath was seven times higher than before swimming. The change in the frequency of micronucleated lymphocytes after swimming increased in association with higher exhaled concentrations of the brominated THMs (p = 0.03 for bromodichloromethane, p = 0.05 for chlorodibromomethane, p = 0.01 for bromoform) but not chloroform. Swimming was not associated with DNA damage detectable by the comet assay. Urine mutagenicity increased significantly after swimming, in association with the higher concentration of exhaled bromoform (p = 0.004). We found no significant associations with changes in micronucleated urothelial cells. CONCLUSIONS: Our findings support potential genotoxic effects of exposure to DBPs from swimming pools. The positive health effects gained by swimming could be increased by reducing the potential health risks of pool water.

Genotoxicity testing of three monohaloacetic acids in TK6 cells using the cytokinesis-block micronucleus assay.

Chemical disinfection of water generates harmful chemical compounds, known as disinfection by-products (DBPs). One class of DBPs is constituted by haloacetic acids (HAAs), the second major group in prevalence (after trihalomethanes) detected in finished drinking water. In this article, we report the results obtained in the evaluation of the chromosome damage induced by three monohaloacetic acids, namely iodoacetic acid (IAA), bromoacetic acid (BAA) and chloroacetic acid (CAA). To evaluate the induction of chromosome damage, we used the cytokinesis-block micronucleus test that measures the ability of genotoxic agents to induce both clastogenic and/or aneugenic effects. No previous data exist on the effects of these compounds on human chromosomes. We tested five doses of each HAA, in addition to the negative and positive controls. The highest dose tested for each HAA was that immediately lower than the dose producing total cytotoxicity. Our results show that none of the three HAAs tested was able to increase significantly the frequency of micronucleus in binucleated TK6 cells, the rank order in decreasing cytotoxicity was IAA > BAA >> CAA.

Genotoxicity of water concentrates from recreational pools after various disinfection methods.

Swimming and hot tub bathing are popular exercises and diversions. Disinfection of recreational pools is essential to prevent outbreaks of infectious disease. Recent research demonstrated an association between the application of disinfectants to recreational pools and adverse health outcomes. These pool waters represent extreme cases of disinfection that differ from disinfecting drinking waters. Pool waters are continuously exposed to disinfectants over average residence times extending to months. Disinfection byproduct (DBP) precursors include natural humic substances plus inputs from bathers through urine, sweat, hair, skin, and consumer products including cosmetics and sunscreens. This study presents a systematic mammalian cell genotoxicity analysis to evaluate different recreational waters derived from a common tap water source. The data demonstrated that all disinfected recreational pool water samples induced more genomic DNA damage than the source tap water. The type of disinfectant and illumination conditions altered the genotoxicity of the water. Accordingly, care should be taken in the disinfectant employed to treat recreational pool waters. The genotoxicity data suggest that brominating agents should be avoided. Combining chlorine with UV may be beneficial as compared to chlorination alone. During the recycling of pool water the organic carbon could be removed prior to disinfection. Behavior modification by swimmers may be critical in reducing the genotoxicity of pool water. Actions such as showering before entering the water and informing patrons about the potential harm from urinating in a pool could reduce the precursors of toxic DBPs.

DNA damage induction by two halogenated acetaldehydes, byproducts of water disinfection.

Drinking water contains disinfection byproducts, generated by the interaction of chlorine (or other disinfecting chemicals) with organic matter, anthropogenic contaminants, and bromide/iodide naturally present in most source waters. One class of these chemicals is the halogenated acetaldehydes (HAs), identified in high quantities when ozone is used as primary or secondary disinfectant. In this study, an analysis of the genotoxic potential of two HAs, namely tribromoacetaldehyde (TBA) and chloral hydrate (CH) has been conducted in human cells (TK6 cultured cells and peripheral blood lymphocytes). The comet assay was used to 1) measure the induction of single and double-strand DNA breaks, 2) evaluate the capacity of inducing oxidative DNA damage, and 3) determine the DNA repair kinetics of the induced primary genetic damage. In addition, chromosome damage, as a measure of fixed damage, was evaluated by means of the micronucleus test. The results of the comet assay show that both compounds are clearly genotoxic, inducing high levels of DNA breaks, TBA being more effective than CH. According to the comet results, both HAs produce high levels of oxidized bases, and the induced DNA damage is rapidly repaired over time. Contrarily, the results obtained in the micronucleus test, which measures the capacity of genotoxic agents to induce clastogenic and aneugenic effects, are negative for the two HAs tested, either using TK6 cells or human peripheral blood lymphocytes. This would indicate that the primary damage induced by the two HAs is not fixed as chromosome damage, possibly due to an efficient repair or the death of damaged cells, which is an important point in terms of risk assessment of DBPs exposure.

Genotoxicity analysis of two hydroxyfuranones, byproducts of water disinfection, in human cells treated in vitro.

In general, water for human consumption is chemically disinfected, usually by adding chlorine. As well as producing safe drinking water however, the chlorine treatment, also results in a number of disinfection byproducts (DBPs). One important class of these DBPs is made up of hydroxyfuranones (HFs). In this article, we report the results of a recent investigation to assess the genotoxicity of two HFs, namely mucobromic acid (MBA) and mucochloric acid (MCA), in cultured human cells. The comet assay is used to measure the induction of primary DNA damage and to determine the DNA repair kinetics and the ability of the tested compounds to cause oxidative damage. In addition, the micronucleus (MN) assay is applied to evaluate chromosome damage. The results of the comet assay reveal that both HFs are clearly genotoxic leading to high levels of DNA breaks, and that MBA is more effective than MCA. According to the comet results, the DNA damage induced by MBA repairs well over time, but not the one induced by MCA. Furthermore, HFs produce high levels of oxidized bases. In contrast, the results from the MN assay, which measures the induction of clastogenic and/or aneugenic effects, are mainly negative for the two HFs tested, although MCA is able to increase significantly the frequency of micronuclei in binucleated TK cells, at the concentration of 10 microM.

Genotoxicity analysis of two halonitromethanes, a novel group of disinfection by-products (DBPs), in human cells treated in vitro.

Halonitromethanes (HNMs) constitute an emerging class of disinfection by-products (DBPs) produced when chlorine and/or ozone are used for water treatment. The HNMs are structurally similar to halomethanes, but have a nitro-group in place of hydrogen bonded to the central carbon atom. Since little information exists on the genotoxic potential of HNMs, a study has been carried out with two HNM compounds, namely trichloronitromethane (TCNM) and bromonitromethane (BNM) by using human cells. Primary damage induction has been measured with the Comet assay, which is used to determine both the repair kinetics of the induced damage and the proportion of induced oxidative damage. In addition, the fixed DNA damage has been evaluated by using the micronucleus (MN) assay. The results obtained indicate that both compounds are genotoxic, inducing high levels of DNA breaks in the Comet assay, and that this DNA damage repairs well over time. In addition, oxidized bases constitute a high proportion of DNA-induced damage (50-75%). Contrarily, no positive effects were observed in the frequency of micronucleus, which measures both clastogenic and aneugenic effects, neither using TK6 cells nor peripheral blood lymphocytes. This lack of fixed genetic damage would minimize the potential mutagenic risk associated with HNMs exposure.