Studies on the in vivo and in vitro mutagenicity and the lipid peroxidation of chlorinated surface (drinking) water in rats and metabolically competent human cells

DNA damage of human derived liver cell line HL-7702 induced by organic extracts from surface water in Pearl River Delta, China

Many organic pollutants attract public health concern due to their genotoxicity. To investigate the genotoxicity of organic matter in surface water of the Pearl River Delta (PRD). Organic substances of 24 samples (dry and wet season) from North River, West River and East River were extracted from 60 L source water by XAD-2 macroporous resin. DNA damage effect of organic extracts was tested in human derived liver cells (HL-7702), using single cell gel electrophoresis (SCGE) assay. The results showed that 100% organic extracts (24/24) could induce DNA damage in HL-7702 cells when the concentration was above 1.0 L surface water/ml culture, no significant difference of DNA damage between dry and wet seasons was observed. The organic substance-induced DNA damage in HL-7702 cells was significantly (P < 0.05) correlated with the contents of Dissolved Organic Carbon in both seasons and Total Suspended Solids in dry season. In conclusion, organic extracts induced genetic damage in HL-7702 cells, indicating potential genotoxicity of organic pollutants of surface water from PRD, South China.

Association of Blood Trihalomethane Concentrations with Risk of All-Cause and Cause-Specific Mortality in U.S. Adults: A Prospective Cohort Study

Water chlorination can lead to the formation of disinfection byproducts, including trihalomethanes (THMs). However, few epidemiologic studies have explored associations between THM exposure and mortality. This study included 6720 adults aged ≥40 years from the National Health and Nutrition Examination Survey 1999-2012 who had blood THM concentrations quantified. A higher risk of all-cause mortality was found across increasing quartile concentrations of blood chloroform (TCM) and total THMs (TTHMs; sum of all four THMs) (both p for trend = 0.02). Adults in the highest quartile of TCM and TTHM concentrations had hazard ratios (HRs) of 1.35 (95% confidence intervals: 1.05-1.74) and 1.37 (1.05-1.79), respectively, for all-cause mortality, compared with adults in the lowest quartile. When cause-specific mortality was evaluated, a positive relationship was found between blood bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (TBM), total brominated THMs (Br-THMs; sum of BDCM, DBCM, and TBM), and TTHM concentrations and risk of cancer death and between blood TCM and TTHMs and risk of other cause (noncancer/nonheart disease) mortality. Our findings suggest that higher exposure to Br-THMs was associated with increased cancer mortality risk, whereas TCM was associated with a greater risk of noncancer/nonheart disease mortality.

Toxicological aspects of trihalomethanes: a systematic review

Chlorine is considered the most used chemical agent for water disinfection worldwide. However, water chlorination can lead to by-product generation which can be toxic to humans. The present study aimed to perform a systematic review on the toxicity of trihalomethanes (THMs) through bioindicators of cytotoxicity, genotoxicity, and mutagenicity. The results showed that studies on the effects of THMs on DNA are a current research concern for evaluating the toxicity of the pure compounds and real samples involving several types including water for recreational use, reused water, and drinking water. THMs deleterious effects have been assessed using several biosystems, where the Ames test along with experimental animal models were the most cited. A wide range of THM concentrations have been tested. Nevertheless, DNA damage was demonstrated, highlighting the potential human health risk. Among the studied THMs, chloroform presented a different action mechanism when compared with brominated THMs, with the former being cytotoxic while brominated THMs (bromodichloromethane, bromoform, and dibromochloromethane) were cytotoxic, genotoxic, and mutagenic. The described evidence in this research highlights the relevance of this topic as a human health issue. Nevertheless, research aimed to represent THMs current exposure conditions in a more accurate way would be needed to understand the real impact on human health.

Primary green turtle (Chelonia mydas) skin fibroblasts as an in vitro model for assessing genotoxicity and oxidative stress

Little is known about the effects of contaminants that accumulate in sea turtles. When in vivo exposure studies have ethical and logistical barriers, as is the case with sea turtles, in vitro tools can provide important information on the effects of contaminants. Several in vitro studies have assessed cytotoxicity of contaminants to sea turtles cells, however to gain a more refined mechanistic understanding of the effects of contaminants, sub-lethal effects also require investigation. Considering the complex mixture of contaminants that sea turtles are potentially exposed to, high throughput testing methods are necessary so that a large number of contaminants (and mixtures) can be rapidly tested. This study examined oxidative stress (reactive oxygen species production) and genotoxicity (micronucleus formation) in primary green turtle skin fibroblasts in response to 16 organic and inorganic contaminants found in coastal environments. Significant induction of oxidative stress was found with Cu, Co, Cr, and Hg. Significant effects on genotoxicity were found with Cu, Co, Cr, Hg, Pb and metolachlor. Effect concentrations from the bioassays were used in a simple risk assessment of turtles worldwide using accumulation values from the literature to identify populations at risk. Cu, Co, Cr and Hg were identified as posing the biggest threat to sea turtles. This study demonstrated the validity of using primary turtle cell cultures in the assessment of risk associated with a large number of contaminants using a high-throughput toxicity testing format.

Increased levels of urinary biomarkers of lipid peroxidation products among workers occupationally exposed to diesel engine exhaust

Diesel engine exhaust (DEE) was found to induce lipid peroxidation (LPO) in animal exposure studies. LPO is a class of oxidative stress and can be reflected by detecting the levels of its production, such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), and etheno-DNA adducts including 1,N(6)-etheno-2'-deoxyadenosine (ɛdA) and 3,N(4)-etheno-2'-deoxycytidine (ɛdC). However, the impact of DEE exposure on LPO has not been explored in humans. In this study, we evaluated urinary MDA, 4-HNE, ɛdA, and ɛdC levels as biomarkers of LPO among 108 workers with exclusive exposure to DEE and 109 non-DEE-exposed workers. Results showed that increased levels of urinary MDA and ɛdA were observed in subjects occupationally exposed to DEE before and after age, body mass index (BMI), smoking status, and alcohol use were adjusted (all p < 0.001). There was a statistically significant relationship between the internal exposure dose (urinary ΣOH-PAHs) and MDA, 4-HNE, and ɛdA (all p < 0.001). Furthermore, significant increased relations between urinary etheno-DNA adduct and MDA, 4-HNE were observed (all p < 0.05). The findings of this study suggested that the level of LPO products (MDA and ɛdA) was increased in DEE-exposed workers, and urinary MDA and ɛdA might be feasible biomarkers for DEE exposure. LPO induced DNA damage might be involved and further motivated the genomic instability could be one of the pathogeneses of cancer induced by DEE-exposure. However, additional investigations should be performed to understand these observations.

Evaluation of genotoxic effects caused by extracts of chlorinated drinking water using a combination of three different bioassays

Potential genotoxic effects of chlorinated drinking water now are of a great concern. In this study, raw water, finished water, and tap water from a water plant in Wuhan, China were collected in two different sampling times of the year (January and July). Genotoxic effects of water extracts were evaluated using a combination of three different bioassays: SOS/umu test, HGPRT gene mutation assay, and micronucleus assay, which were separately used to detect DNA damage, gene mutation, and chromosome aberration. The results of three different bioassays showed that all water samples in January and July induced at least one types of genotoxic effects, of which the DNA-damage effects were all detectable. The levels of DNA-damage effects and gene-mutation effects of finished water and tap water in January were higher than those in July. Chlorination could increase the DNA-damage effects of drinking water in January and the gene-mutation effects of drinking water in both January and July, but did not increase the chromosome-aberration effects of drinking water in both January and July. Our results highlighted the importance of using a combination of different bioassays to evaluate the genotoxicity of water samples in different seasons.

Evaluation of the genotoxicity of waters impacted by domestic and industrial effluents of a highly industrialized region of São Paulo State, Brazil, by the comet assay in HTC cells

The problems that most affect the quality of the waters of rivers and lakes are associated with the discharges performed in these environments, mainly industrial and domestic effluents inappropriately treated or untreated. The comet assay is a sensitive tool and is recommended for studies of environmental biomonitoring, which aim to determine the genotoxicity potential of water pollutants. This study aimed to assess the genotoxic potential of the Ribeirão Tatu waters, region of Limeira, São Paulo (SP), by the comet assay with mammalian cells (hepatoma tissue culture (HTC)). Water samples were collected along the Ribeirão Tatu at three distinct periods: November 2008, February 2009 and August 2009, and five collection sites were established: P1, source of the stream; P2, site located downstream the urban perimeter of the municipality of Cordeirópolis and after receiving the pollution load of this city; P3, collection site located upstream the urban perimeter of the city of Limeira; P4, urban area of Limeira; and P5, rural area of Limeira, downstream the discharges of the city sewage. The results showed that for the November 2008 collection, there was no water sample-induced genotoxicity; for the February 2009 collection, the sites P1 and P2 were statistically significant in relation to the negative control (NC), and for the August 2009 collection, the site P5 was statistically significant. These results could be explained by the content of different metals during the different seasons that are under the influence of domestic, industrial and agricultural effluents and also due to the seasonality, since the water samples collected in the period of heavy rain (February 2009) presented a higher genotoxicity possibly due to the entrainment of contaminants into the bed of the stream promoted by the outflow of rainwaters. The comet assay showed to be a useful and sensitive tool in the evaluation of hydric resources impacted by pollutants of diverse origins, and a constant monitoring should be done in order to verify the influence of different factors (season, amount of contaminants) in the water quality.

A comparative toxicity evaluation of Escherichia coli-targeted ssDNA and chlorine in HepG2 cells

In this study, a comparative assessment of the effectiveness of ssDNA and chlorine as disinfectants for treating water contaminated with Escherichia coli (E. coli) was investigated on the basis of cytotoxicity and genotoxicity. The gene targets addressed for the ssDNA based inhibition method were marA (multiple antibiotic resistance) and groL (essential gene Hsp60) in E. coli. Based on the maximum log reduction in E. coli cell numbers when compared to no ssDNA control, groL-1 was chosen as the optimized ssDNA for gene silencing-based inactivation. For toxicity assessment, HepG2 cells were exposed to extracts corresponding to concentrations of 0.2, 1, 5, 25 and 50 mL water/mL medium of chlorine doped water and 1, 10, 100, 300 nM of ssDNA. Compared with ssDNA, HepG2 cells exposed to extracts of chlorine doped water for 24 h showed higher cytotoxicity, caspase 3/7 levels, DNA damage, micronuclei frequency, and decreased cell viability. Water doped with chlorine was found to be more toxic than that by ssDNA when exposed to HepG2 cells. The results of this study provide a scientific basis for comparative evaluation of new and conventional disinfection methods by taking into consideration the outcome of cytotoxicity and genotoxicity assessments.

In vitro toxicity of surface water disinfected by different sequential treatments

The in vitro toxicity of extracts of Hanjiang water disinfected by different sequential treatments was evaluated. Hanjiang water was disinfected using ozone, chloride dioxide or chlorine as the primary disinfectant followed by chlorine as the secondary disinfectant. HepG(2) cells were exposed to extracts corresponding to concentrations of 0.2, 1, 5, 25 and 125 mL water/mL medium. Compared with control, HepG(2) cells exposed to extracts of raw water and all disinfected water for 24h increased oxidative stress level, DNA damage and micronuclei frequency, and decreased cell viability. Water disinfected by Cl(2)+Cl(2) had the highest DNA double-strand breaks. All disinfected water and raw water increased micronuclei frequency via clastogenic and aneugenic effects. Oxidative stress induced DNA strand breaks and micronuclei frequency and therefore reduced cell viability either in disinfected water or raw water. Compared with raw water, water after disinfection increased DNA strand breaks, decreased cell viability and changed oxidative stress potential. Compared with chlorination, sequential treatment using O(3) or ClO(2) as primary disinfectant followed by chlorine disinfection reduced chlorinated by-products, DNA double-strand breaks and cell viability, but did not decrease micronuclei frequency and other DNA damage such as DNA single-strand break, alkali liable sites and incomplete excision sites. Sequential treatments did not significantly reduce in vivo toxicity of disinfected Hanjiang water.

A stable and sensitive testing system for potential carcinogens based on DNA damage-induced gene expression in human HepG2 cell

In order to analyze potential carcinogenic and genotoxic responses caused by exposure to pollutants existing in environment, a screening method has been established in our laboratory that uses a stably transfected HepG2 cell lines containing gadd153 promoter regions which drive a luciferase reporter gene. Activation of the exogenous gadd153 promoter was quantified using the luciferase activity following drug exposure. Twenty four agents were used to evaluate this screening assay. We selected the agents, ranging from DNA alkylating agents, oxidative agent, radiation, DNA cross-linking agent, nongenotoxic carcinogens, precarcinogenic agents, which included cadmium chloride, chromium trichloride, mercuric chloride, lead nitrate, dichloro-diphenyl-trichloroethane, deltamethrin, biphenylamine, 2-aminofluorene, benzo[a]pyrene, 2,3,7,8,-tetracblorodibenzo-p-dioxin, diethyl-stilbestrol, carbon tetrachloride, mitomycin C, hydroxycamptothecin, UV, sodium fluoride, acrylamide, hydrogen peroxide. In addition, two complex genotoxic agents (water samples) existing in the environment were selected. The results showed that all 20 tested known carcinogenic and genotoxic agents were able to induce gadd153-Luc expression at a sublethal dose. In contrast, four tested non-carcinogens, included 4-acetylaminofluorene, pyrene, benzylpenicillin sodium and vitamin C, were unable to induce gadd153-Luc expression. In conclusion, this reporter system can facilitate in vitro screening for potential carcinogens. Therefore, the gadd153-Luc test system we have developed appears to be a useful and complementary system to existing genotoxic and mutagenic tests.

Toxicity evaluation of surface water treated with different disinfectants in HepG2 cells

It is well known that water disinfection through chlorination causes the formation of a mixture of disinfection by-products (DBPs), many of which are genotoxic and carcinogenic. To demonstrate the formation of such compounds, a pilot water plant supplied with water from Lake Trasimeno was set up at the waterworks of Castiglione del Lago (PG, Italy). The disinfectants, continuously added to pre-filtered lake water flowing into three different basins, were sodium hypochlorite, chlorine dioxide and peracetic acid, an alternative disinfectant used until now for disinfecting waste waters, but not yet studied for a possible use in drinking water treatment. The aim of this study was to evaluate the formation during the disinfection processes of some toxic compounds that could explain the genotoxic effects of drinking waters. Differently treated waters were concentrated by solid-phase adsorption on silica C(18) columns and toxicity was assessed in a line of human hepatoma cells (HepG2), a metabolically competent cellular line very useful for human risk evaluation. The seasonal variability of the physical-chemical water characteristics (AOX, UV 254 nm, potential formation of THM, pH and temperature) made indispensable experimentation with water samples taken during the various seasons. Autumn waters cause greater toxicity compared to those of other seasons, in particular dilution of the concentrate at 0.5l equivalent of disinfected waters with chlorine dioxide and peracetic acid causes a 55% reduction in cellular vitality while the cellular vitality is over 80% with the all other water concentrates. Moreover it is very interesting underline that non-cytotoxic quantities of the autumnal water concentrates cause, after 2h treatment, a decrease in GSH and a statistically significant increase in oxygen radicals, while after prolonged treatment (24h) cause a GSH increase, without variations in the oxygen radical content. This phenomenon could be interpreted as the cellular adaptation response to an initial oxidative stress.

2,4-Diaminotoluene (2,4-DAT)-induced DNA damage, DNA repair and micronucleus formation in the human hepatoma cell line HepG2

2,4-Diaminotoluene (2,4-DAT) is a widely used industrial intermediate and human exposure is possible in the dye and plastics industries. We investigated the genotoxicity of the environmental pollutant, 2,4-DAT, in human HepG2 cells using the unscheduled DNA synthesis (UDS) test, the micronucleus (MN) assay and single-cell gel electrophoresis (SCGE). 2,4-DAT was first tested by the RNA synthesis inhibition test as a cytotoxicity assay: the IC(50) of 2,4-DAT was 5.2 mM after 20 h of exposure. The compound had a genotoxic effect at concentrations from 1.45 to 6.80 mM in both micronucleus and comet assays. In the micronucleus assay, the number of MN/1000 BNC was 3.5 times higher at a concentration of 6.80 mM 2,4-DAT than in the negative control. At the same concentration, DNA migration (SCGE) showed an Olive tail moment (OTM) of 3.56+/-0.45, as compared to 0.19+/-0.02 for the negative control. The UDS test detected genotoxic effects at lower concentrations than did the other assays (0.01-5 mM). The percentage of cells in repair increased in a concentration-dependent manner to a maximum of 57% at 1mM. At the highest concentration tested (5 mM), the NNG/cell score was 13.6+/-0.5 whereas it was -2.7+/-0.5 for the negative control. These data, based on various endpoints, show a midly genotoxic effect of 2,4-DAT in the HepG2 cells and confirm that this cell line is a suitable model to study the toxic effects of aromatic amines.

Chlorinated river and lake water extract caused oxidative damage, DNA migration and cytotoxicity in human cells

Consumption of chlorinated drinking water is suspected to be associated with adverse health effects, including mutations and cancer. In the present study, the genotoxic potential of water from Donghu lake, Yangtze river and Hanjiang river in Wuhan, an 8-million metropolis in China, was investigated using HepG2 cells and the alkaline version of the comet assay. It could be shown that all water extracts caused dose-dependent DNA migration in concentrations corresponding to dried extracts of 0.167-167 ml chlorinated drinking water per ml medium. To explore whether the intracellular redox status is regulated by chlorinated drinking water, we determined lipid peroxidation (LPO) and depletion of reduced glutathione (GSH). The malondialdehyde (thiobarbituric acid (TBA)-reactive aldehydes) concentration increased after chlorinated drinking water treatment of HepG2 cells in a dose-dependent manner, the GSH content decreased. The activity of lactate dehydrogenase (LDH) increased in chlorinated drinking water treated HepG2 cells indicating cytotoxicity. In accordance with former studies which dealt with in vivo and in vitro micronucleus induction the present study shows that chlorinated drinking water from polluted raw water may entail genetic risks.

Study of potential toxic effects on rainbow trout hepatocytes of surface water treated with chlorine or alternative disinfectants

This study evaluates the effects of disinfection on the formation of toxic compounds in lake water treated with sodium hypochlorite, chlorine dioxide and peracetic acid (a disinfectant not previously used in drinking water processes). Chlorine reacts with the natural organic matter or contaminants in surface waters and produces a complex mixture of disinfection by-products (DBPs), some of which have been shown to be carcinogenic, mutagenic and/or teratogenic in animal studies. To define the potential toxicity on aquatic animals, disinfected drinking waters obtained from a pilot plant fed with water coming from Lake Trasimeno (Perugia) were collected, adsorbed by using silica C18 cartridges, and then eluted in sequence with ethylacetate, dichloromethane and methanol. The eluates were concentrated under vacuum and resuspended in dimethylsulfoxide (DMSO). Primary cultures of rainbow trout hepatocytes were exposed to three amounts of water concentrate (equivalent to 0.5, 0.25 and 0.125 l of disinfected water per ml of culture medium) for 24 h at 20 degrees C, after which their viability, glutathione content (GSH), free radical production (ROS) and cytochrome P4501A3 expression were determined. The disinfected water samples were collected during different seasons in order to evaluate a possible correlation between seasonal water variations and formation of toxic compounds. None of the water concentrates showed any cytotoxic effect or variations in GSH content, but significant increases in ROS production were detected in the autumn water concentrates from the treatments with sodium hypochlorite and chlorine dioxide. Cytochrome P4501A3 expression was not modified in the hepatocytes exposed to the water concentrates irrespective to the sampling season.

Chromosome damage in peripheral lymphocytes of sheep induced by chlorine in drinking water

The potential of chromosomal damage associated with the effects of chlorine in drinking water was evaluated using chromosome aberrations and micronuclei as cytogenetic endpoints in the lymphocytes of peripheral blood of ewe lambs. The study assessed the in vivo effects of high chlorine doses (1.8 mg l(-1), based on Savo-Super disinfectant) in drinking water on the peripheral lymphocytes of sheep after 30 days. The frequency of aberrant cells (AB.C.) in the experimental and control groups was 31.80+/-13.68% AB.C. and 4.50+/-2.07% AB.C. respectively, and the increased AB.C. in the treated group was highly significant (P=/<0.001). In the experimental group chromatid breaks (26.20+/-10.47%) and gaps (24.20+/-13.94%) were the dominant types of aberrations, but statistically significant chromosome gaps and exchanges were also present. The frequency of micronuclei in peripheral lymphocytes of sheep in the control group was 21.17+/-4.36 per 1,000 binucleated cells and 64.20+/-22.51 per 1,000 binucleated cells in the experimental group. A significant increase in the frequency of micronuclei in peripheral lymphocytes of sheep was observed between the two groups (P=0.001).

DNA damage caused by extracts of chlorinated drinking water in human derived liver cells (HepG2)

Dong (D) lake and the Yangtze (Y) river are the main water supplies of the city of Wuhan, PR China. In the present study, the genotoxic effect of chlorinated drinking water (CDW) processed from raw water of D lake and Y river was evaluated in human HepG2 cells using the Comet assay and the micronucleus test. For that, HepG2 cells were exposed to XAD extracts of CDW corresponding to 0.167, 1.67, 16.7 and 167 ml CDW/ml cell culture. All CDW extracts caused a significant and dose-dependent increase of DNA migration in HepG2 cells. The level of DNA damage varied depending on the sampling time (season) and sampling site. The lowest concentration which caused a significant increase of DNA migration was 1.67 ml CDW/ml culture for water samples collected in August. Water samples collected in March showed their lowest observable effect levels in 167 ml and 16.7 ml CDW/ml culture for Y river and D lake, respectively. Additionally, significant increases of micronuclei (MN) frequencies were found in HepG2 cells after CDW treatment. However, in the MN assay the CDW samples collected in March exhibited higher genotoxicity than the August samples. In conclusion, HepG2 cells provide a useful tool for the detection of genotoxic effects of environmental mixtures.

Evaluation of EMS-induced DNA damage in the single cell gel electrophoresis (Comet) assay and with flow cytometric analysis of micronuclei

Toxic agents in the environment pose serious threats to ecosystems and to the public health. The single cell gel electrophoresis (SCGE) or Comet assay quantitatively measures genomic damage as DNA strand breaks. The micronucleus (MCN) test is an established assay that measures chromosomal damage. Micronuclei are formed from chromosome fragments or from whole chromosomes that have not undergone mitosis properly. This test is usually conducted microscopically. However, micronuclei can also be analyzed using flow cytometry. Chinese hamster ovary (CHO) cells were exposed to ethylmethanesulfonate (EMS), for 4 h in a total volume of 25 microl. These cells were immediately analyzed for genomic DNA damage by SCGE. In concurrent parallel experiments, CHO cells were treated with EMS in 6-well plates for 4 h, the cells were washed and fresh medium was added. The cells were allowed to grow for 45 to 48 h to express micronuclei. The data demonstrated that both DNA strand breaks and micronuclei were induced in a significant and concentration-dependent manner. There was a significant and high correlation (r = 0.91; P < or = 0.001) between the acute induction of DNA strand breaks and the subsequent generation of micronuclei. These data indicate that using molecular and computer technologies, the genotoxic impact of toxic and environmental agents can be rapidly and comprehensively evaluated in mammalian cell systems.