Individual Disinfection By-products Research Articles

Effects of ozone dose on brominated DBPs in subsequent chlor(am)ination: A comprehensive study of aliphatic, alicyclic and aromatic DBPs

Ozone‒chlor(am)ine is a commonly used combination of disinfectants in drinking water treatment. Although there are quite a few studies on the formation of some individual DBPs in the ozone‒chlor(am)ine disinfection, an overall picture of the DBP formation in the combined disinfection is largely unavailable. In this study, the effects of ozone dose on the formation and speciation of organic brominated disinfection byproducts (DBPs) in subsequent chlorination, chloramination, or chlorination‒chloramination of simulated drinking water were investigated. High-molecular-weight, aliphatic, alicyclic and aromatic brominated DBPs were selectively detected and studied using a powerful precursor ion scan method with ultra performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (UPLC/ESI-tqMS). Two groups of unregulated yet relatively toxic DBPs, dihalonitromethanes and dihaloacetaldehydes, were detected by the UPLC/ESI-tqMS for the first time. With increasing ozone dose, the levels of high-molecular-weight (m/z 300–500) and alicyclic and aromatic brominated DBPs generally decreased, the levels of brominated aliphatic acids were slightly affected, and the levels of dihalonitromethanes and dihaloacetaldehydes generally increased in the subsequent disinfection processes. Despite different molecular compositions of the detected DBPs, increasing ozone dose generally shifted the formation of DBPs from chlorinated ones to brominated analogues in the subsequent disinfection processes. This study provided a comprehensive analysis of the impact of ozone dose on the DBP formation and speciation in subsequent chlor(am)ine disinfection.

Risks of obstructive genitourinary birth defects in relation to trihalomethane and haloacetic acid exposures: expanding disinfection byproduct mixtures analyses using relative potency factors.

Some disinfection byproducts (DBPs) are teratogens based on toxicological evidence. Conventional use of predominant DBPs as proxies for complex mixtures may result in decreased ability to detect associations in epidemiological studies. We assessed risks of obstructive genitourinary birth defects (OGDs) in relation to 12 DBP mixtures and 13 individual component DBPs. We designed a nested registry-based case-control study (210 OGD cases; 2100 controls) in Massachusetts towns with complete quarterly 1999-2004 data on four trihalomethanes (THMs) and five haloacetic acids (HAAs). We estimated temporally-weighted average DBP exposures for the first trimester of pregnancy. We estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for OGD in relation to individual DBPs, unweighted mixtures, and weighted mixtures based on THM/HAA relative potency factors (RPF) from animal toxicology data for full-litter resorption, eye defects, and neural tube defects. We detected elevated aORs for OGDs for the highest of bromodichloromethane (aOR = 1.75; 95% CI: 1.15-2.65), dibromochloromethane (aOR = 1.71; 95% CI: 1.15-2.54), bromodichloroacetic acid (aOR = 1.56; 95%CI: 0.97-2.51), chlorodibromoacetic acid (aOR = 1.97, 95% CI: 1.23-3.15), and tribromoacetic acid (aOR = 1.90; 95%CI: 1.20-3.03). Across unweighted mixture sums, the highest aORs were for the sum of three brominated THMs (aOR = 1.74; 95% CI: 1.15-2.64), the sum of six brominated HAAs (aOR = 1.43; 95% CI: 0.89-2.31), and the sum of nine brominated DBPs (aOR = 1.80; 95% CI: 1.05-3.10). Comparing eight RPF-weighted to unweighted mixtures, the largest aOR differences were for two HAA metrics, which both were higher with RPF weighting; other metrics had reduced or minimally changed ORs in RPF-weighted models.

Bacterial diversity across four drinking water distribution systems in Croatia: impacts of water management practices and disinfection by-products.

Several factors may impact bacterial diversity in drinking water distribution systems (DWDSs) including the origin of the raw water, the water treatment technologies, and the disinfection practices applied. 16S rRNA metabarcoding was used for the in-depth characterization of bacterial communities in the four studied Croatian DWDSs (A, B, C, D) two of which had residual disinfectant (A, B) and two were without (C, D), while only B utilized the conventional water treatment technology. Significantly higher diversity and species richness were evidenced in non-disinfected DWDSs (p<0.05) compared to disinfected DWDSs. The phylum Proteobacteria was the most abundant in all the DWDSs, being proportionately higher in non-disinfected systems (p<0.05). The most abundant genera in DWDS-A Mycobacterium and Sphingomonas both positively correlated, whereas Lactobacillus negatively correlated with the concentration of disinfection by-products (DBPs) as a sum of haloacetic acids (HAAs). Conversely, the genus Ralstonia positively correlated with the individual DBP dichloroacetic acid. These results indicate that genera Sphingomonas, Mycobacterium, Lactobacillus and Ralstonia could have an effect on promoting the formation of DBPs, in a similar manner to how negatively correlated taxa may influence their degradation.

Effect of chlorine dioxide pre-oxidation on algal non-protein amino acid degradation and DBPs formation during subsequent chlor(am)ination

As a neurotoxin produced by cyanobacteria, 2,4-diaminobutyric acid (DAB) posed a significant threat to human health and served as an important precursor to disinfection by-products (DBPs). In this study, ClO2 showed the highest DAB oxidation efficiency among the four oxidants, in the order of ClO2 (86%) > HOCl (80%) > KMnO4 (20%) > NH2Cl (13%). The increase of ClO2 dosage (from 0.06 to 1.4 mg L-1) not only increased the oxidation efficiency of DAB, but also decreased the formation of DBPs after ClO2 pre-oxidation during post-chlorination, but the DBPs formation varied during post-chloramination. The enhanced formation of dichloroacetic acid (DCAA) and dichloroacetonitrile (DCAN) should be of concern when ClO2 pre-oxidation was performed at pH 7.0. In the presence of Br−, the overall concentration of formed THMs and brominated species increased. ClO2 pre-oxidation of β-N-methylamino-l-alanine (BMAA), alanine, leucine, and serine followed by post-chloramination has advantages over post-chlorination in controlling the overall and individual DBPs concentration. A possible degradation pathway and reaction schemes during ClO2 pre-oxidation of DAB were proposed. ClO2 pre-oxidation followed by post-chloramination could be an effective treatment process in the abatement of both DAB and toxicity. Results of this study about DAB oxidation and DBP formation contributed to the guidance of ClO2 pre-oxidation in the water treatment plants to cope with cyanobacterial blooms.

Disinfection byproducts in chlorinated or brominated swimming pools and spas: Role of brominated DBPs and association with mutagenicity

Although the health benefits of swimming are well-documented, health effects such as asthma and bladder cancer are linked to disinfection by-products (DBPs) in pool water. DBPs are formed from the reaction of disinfectants such as chlorine (Cl) or bromine (Br) with organics in the water. Our previous study (Daiber et al., Environ. Sci. Technol. 50, 6652; 2016) found correlations between the concentrations of classes of DBPs and the mutagenic potencies of waters from chlorinated or brominated swimming pools and spas. We extended this study by identifying significantly different concentrations of 21 individual DBPs in brominated or chlorinated pool and spa waters as well as identifying which DBPs and additional DBP classes were most associated with the mutagenicity of these waters. Using data from our previous study, we found that among 21 DBPs analyzed in 21 pool and spa waters, the concentration of bromoacetic acid was significantly higher in Br-waters versus Cl-waters, whereas the concentration of trichloroacetic acid was significantly higher in Cl-waters. Five Br-DBPs (tribromomethane, dibromochloroacetic acid, dibromoacetonitrile, bromoacetic acid, and tribromoacetic acid) had significantly higher concentrations in Br-spa versus Cl-spa waters. Cl-pools had significantly higher concentrations of Cl-DBPs (trichloroacetaldehyde, trichloromethane, dichloroacetic acid, and chloroacetic acid), whereas Br-pools had significantly higher concentrations of Br-DBPs (tribromomethane, dibromoacetic acid, dibromoacetonitrile, and tribromoacetic acid). The concentrations of the sum of all 4 trihalomethanes, all 11 Br-DBPs, and all 5 nitrogen-containing DBPs were each significantly higher in brominated than in chlorinated pools and spas. The 8 Br-DBPs were the only DBPs whose individual concentrations were significantly correlated with the mutagenic potencies of the pool and spa waters. These results, along with those from our earlier study, highlight the importance of Br-DBPs in the mutagenicity of these recreational waters.

Evaluation of N-acetylcysteine and glutathione as quenching agents for the analysis of halogenated disinfection by-products

Disinfection by-products (DBPs), formed from the reactions of disinfectants with natural organic matter and halides in drinking water, were considered to be cytotoxic and genotoxic, and might trigger various cancers. The relatively low concentration of DBPs in finished water (low µg/L or even ng/L levels) and the interference from water matrix inhibited in situ determination of DBPs. Moreover, the further formation and degradation of DBPs by disinfectants during the holding time (several hours to several days) from sample collection to analysis could adversely affect the determination of DBPs. To obtain accurate, precise and reliable data of DBP occurrence and formation, robust and reliable sample preservation is indispensable. However, the commonly used quenching agents (e.g., sodium sulfite, sodium thiosulfate, and ascorbic acid) for sample preservation can decompose reactive DBPs by reductive dehalogenation. This study evaluated the performance of N-acetylcysteine (NAC) and glutathione (GSH) as quenching agents for the analysis of halogenated DBPs by investigating the stoichiometry of the disinfectant-quenching agent reaction, the formation of DBPs during chlor(am)ination of NAC or GSH, and the effects of NAC or GSH on the stability of 18 individual DBPs and total organic halogen (TOX). Based on the results of this study, NAC and GSH were considered to be ideal quenching agents for the analysis of most DBPs and TOX, except halonitromethanes.

Formation and control of C- and N-DBPs during disinfection of filter backwash and sedimentation sludge water in drinking water treatment

Drinking water treatment plants (DWTPs) produce filter backwash water (FBW) and sedimentation sludge water (SSW) that may be partially recycled to the head of DWTPs. The impacts of key disinfection conditions, water quality parameters (e.g., disinfection times, disinfectant types and doses, and pH values), and bromide concentration on controlling the formation of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloacetamides (HAMs) during disinfection of FBW and SSW were investigated. Concentrations of most disinfection byproducts (DBPs) and associated calculated toxicity increased with extended chlorination for both FBW and SSW. During chlorination of both FBW and SSW, elevated chlorine doses significantly increased THM yields per unit dissolved organic carbon (DOC), but decreased HAN and HAM yields, with minimum effect on HAA yields. Chloramine disinfection effectively inhibited C-DBP formation but promoted N-DBPs yields, which increased with chloramine dose. Calculated toxicities after chloramination increased with chloramine dose, which was opposite to the trend found after free chlorine addition. An examination of pH effects demonstrated that C-DBPs were more readily generated at alkaline pH (pH=8), while acidic conditions (pH=6) favored N-DBP formation. Total DBP concentrations increased at higher pH levels, but calculated DBP toxicity deceased due to lower HAN and HAM concentrations. Addition of bromide markedly increased bromo-THM and bromo-HAN formation, which are more cytotoxic than chlorinated analogues, but had little impact on the formation of HAAs and HAMs. Bromide incorporation factors (BIFs) for THMs and HANs from both water samples all significantly increased as bromide concentrations increased. Overall, high bromide concentrations increased the calculated toxicity values in FBW and SSW after chlorination. Therefore, while currently challenging, technologies capable of removing bromide should be explored as part of a strategy towards controlling cumulative toxicity burden (i.e., hazard) while simultaneously lowering individual DBP concentrations (i.e., exposure) to manage DBP risks in drinking water.

Chloramination of iopamidol- and bromide-spiked waters containing natural organic matter

AbstractIopamidol (an iodinated X-ray contrast medium) and bromide are precursors in the formation of halogenated disinfection byproducts (DBPs). The interactions of these precursors are vital to elucidate the formation of halogenated DBPs during chloramination. This work investigated the formation of total organic halogen and select individual DBPs in two laboratory-chloraminated source waters containing iopamidol and bromide. Experiments were carried out in batch reactors containing Barberton source water (BSW) and Cleveland BSW (CSW), spiked with iopamidol (5 μM), bromide (15 μM), and 100 μM monochloramine. Total organic iodine concentrations were approximately equal regardless of source water since they are mostly unreacted iopamidol and iopamidol DBPs. Almost equal amounts of total organic chlorine (3–4 nM) were produced in the source waters, but higher quantities of total organic bromine were formed in BSW than CSW. Substantial quantities of regulated trihalomethanes (THMs) and haloacetic acids (HAAs) were formed in the source waters, along with appreciable concentrations of iodinated trihalomethanes (CHBrClI, CHCl2I, and CHBr2I). Low concentrations of iodo-HAAs were detected, especially at low pH. Overall, bromide concentrations appeared to suppress iodo-DBP formation during chloramination of iopamidol in the presence of natural organic matter. A good correlation (R2 = 0.801) between the yields of regulated DBPs and iodo-DBPs was observed.

Exposure Misclassification: Temporal and Spatial Variability in Estimates of Individual Species and Mixtures of Disinfection Byproducts

Disinfection of drinking water is a public health advance, but the potential risk of unintended consequences of disinfection byproduct (DBP) formation remains unclear. Over 600 DBPs have been identified to date, although most have not been analytically quantified in disinfected drinking water. Some DBP exposures occur through multiple routes which can complicate exposure assessment in epidemiological studies especially based on aggregate data derived from routinely-collected monitoring data. Therefore it is important to quantify the spatiotemporal variability in occurrence to minimize measurement error and exposure misclassification. In the absence of biomonitoring data, concentration-based exposure scores based on routinely-collected monitoring data can be spatial water system averages or location-specific estimates. However, intra-water system variation in DBP concentrations results from formation and degradation processes occurring over space and residence time. Temporal variability can also occur from diurnal variation to longer-term trends such as seasonality noted for trihalomethanes (THMs) and haloacetic acids (HAAs). Temporally averaged data may estimate lifetime exposure for cancer outcomes or trimester-specific windows for developmental effects, but they ill fully account for the potential impact of peak exposures. Although the DBP surrogacy issue is beyond the scope here, data availability limitations may preclude examination and delineation of potential risk for individual DBPs or DBP mixtures especially when the measurement error structures can vary due to use of aggregate exposure estimates. With few DBPs regulated or routinely measured, this review will characterize strengths and limitations of existing approaches based on HAAs and THMs and will offer evidence from simulations and sensitivity analyses and offer recommendations to help address the aforementioned challenges. Disclaimer: The views expressed in this abstract are those of the author and do not necessarily reflect the views or policies of the U.S. EPA. Keywords: Water, water quality, disinfection byproducts, environmental epidemiology

Disinfection byproducts and their toxicity in wastewater effluents treated by the mixing oxidant of ClO2/Cl2

Mixing oxidant of chlorine dioxide (ClO2) and chlorine (Cl2) often applied in water disinfection. Two secondary wastewater effluents at different ammonium-N levels (0.1 and 1.6 mg N L−1) were treated with the mixing oxidant (ClO2/Cl2) to evaluate the formation of disinfection byproducts (DBPs) and the associated cytotoxicity of treated wastewaters. The total chlorine concentrations of ClO2 and Cl2 were maintained at 10 mg L−1 as Cl2 with varied mixing ratios of ClO2 to Cl2. The formation of 37 halogenated DBPs, including nitrogenous, brominated and iodinated analogues, and 2 inorganic DBPs (chlorite and chlorate) was examined. The sum concentrations of the halogenated DBPs were reduced remarkably with decreasing Cl2 percentages, but each individual DBP group had distinct features. The regulated trihalomethanes reduced the most when ClO2 was present in chlorination, but decreasing Cl2 percentage from 70% to 30% was not quite effective to reduce the formation of iodinated trihalomethanes, haloacetic acids and haloacetontriles in low ammonium-N wastewater. The bromine and iodine substitution factors tend to increase with decreasing Cl2 percentages, indicating that destruction of DBP precursors by ClO2 favored bromine and iodine incorporation. Additionally, decreasing Cl2 percentages in the mixing oxidant (ClO2/Cl2) was often accompanied with lower chlorate formation but higher chlorite formation. The toxicity of treated wastewaters was evaluated through two approaches: the calculated cytotoxicity based on the concentrations of detected DBPs and the experimental cytotoxicity using the Chinese hamster ovary (CHO) cells. The calculated cytotoxicity decreased with decreasing Cl2 percentages, with haloacetonitriles and haloacetaldehydes as predominate contributors. However, the experimental cytotoxicity tests showed that treatment of high ammonium-N wastewater with ClO2/Cl2 exhibited considerable higher (> 3 times) cytotoxicity potency than using single disinfectant.

Ingested nitrate, disinfection by-products, and risk of colon and rectal cancers in the Iowa Women's Health Study cohort

BackgroundN-nitroso compounds (NOC) formed endogenously after nitrate/nitrite ingestion and disinfection by-products (DBPs) are suspected colorectal carcinogens, but epidemiologic evidence of these associations is limited. ObjectivesWe investigated the relationship between drinking water exposures and incident colorectal cancers in a cohort of postmenopausal women. MethodsUsing historical nitrate-nitrogen (NO3-N) measurements and estimates of total trihalomethanes (TTHM), the sum of 5 or 6 haloacetic acids (HAAs), and individual DBPs in public water supplies (PWS), we computed average exposures and years of exposure above one-half the U.S. maximum contaminant level (>1/2-MCL; >5 mg/L NO3-N and >40 μg/L TTHM). Nitrate/nitrite intakes from dietary sources were estimated using a food frequency questionnaire. We estimated hazard ratios (HR) and 95% confidence intervals (CI) from Cox regression models. We assessed NO3-N interactions with DBPs and with factors influencing endogenous NOC formation. ResultsWe identified 624 colon and 158 rectal cancers (1986–2010) among 15,910 women reporting PWS use >10 years. Ingestion of NO3-N from drinking water was not associated with risk. Colon cancer risks were non-significantly associated with the average TTHM levels >17.7 μg/L (HRQ5vsQ1 = 1.13, CI = 0.89–1.44; ptrend = 0.11) and were elevated for any duration of exposure >1/2-MCL. Rectal cancer risks were associated with the highest TTHM levels (HRQ5vsQ1 = 1.71, CI = 1.00–2.92; ptrend = 0.22) but not with years >1/2-MCL. Bromodichloromethane (HRQ4vsQ1 = 1.89, CI = 1.17–3.00; ptrend = 0.09) and trichloroacetic acid (HRQ4vsQ1 = 1.92, CI = 1.20–3.09; ptrend = 0.18) levels were also associated with risk of rectal cancer. We found no evidence of interaction between TTHM and NO3-N on the risk of either cancer. Dietary analyses yielded a positive colon cancer association with red meat, but not with processed meat intake or estimated nitrate/nitrite from specific dietary sources. ConclusionsOur results suggest that exposure to TTHM in drinking water is associated with increased risk of rectal cancer. Positive findings for individual THMs and HAAs for both colon and rectal cancers require replication in other studies. We found no associations for nitrate overall or in subgroups with presumed higher NOC exposure.

Conversion of haloacid disinfection byproducts to amino acids via ammonolysis

Haloacetic acids (HAAs) are the major disinfection byproducts (DBPs) that are formed during chlorination of drinking water. In this paper, the conversion of HAAs to amino acids (e.g., glycine) via ammonolysis was studied. First, a new and sensitive method for detecting glycine was developed by setting selected ion recording m/z 76 in positive electrospray ionization mass spectrometry coupled with ultra performance liquid chromatography. Second, among the mono-HAAs under the same test conditions, iodoacetic acid (49.3%) showed a considerably higher conversion to glycine during ammonolysis than chloroacetic acid (4.2%) and bromoacetic acid (27.7%). The conversion of iodoacetic acid to glycine increased with increasing temperature, increasing reaction time, or decreasing the ratio of (NH4)2CO3 to NH3·H2O in the aminating agent. Hydrolysis of iodoacetic acid to glycolic acid was also observed during ammonolysis, and it accounted for at most 50% of the iodoacetic acid conversion. The conversion to amino acids and the hydrolysis were the two major pathways during ammonolysis of HAAs. Third, compared with the iodoacetic acid sample and the simulated tap water sample without ammonolysis, the developmental toxicity of the corresponding samples with ammonolysis decreased by up to 10.4% and 32.1%, respectively. The ammonolysis was thus demonstrated to be a detoxification process for both individual HAAs and DBP mixture in chlorinated tap water. In practice, the ammonolysis of haloacid DBPs in tap water may be realized by simply adding an appropriate amount of an aminating agent during cooking.

Effects of chlorination on the fluorescence of seawater: Pronounced changes of emission intensity and their relationships with the formation of disinfection byproducts

Chlorination of coastal (CS) and deep ocean (DO) seawater was accompanied by a prominent decrease (of up to 70%) of the intensity of its emission which was measured using a 315 nm excitation wavelength. Deconvolution of the emission spectra of CS and DO seawater showed that these spectra comprised three Gauss-shaped bands. The intensities of two of these bands decreased rapidly as the halogenation proceeded. For both DO and CS seawater, two stages of changes of their fluorescence were observed. The first stage in which the relative changes of the fluorescence intensity (ΔF/F) were between zero to 0.30 and 0.40 was not accompanied by the release of individual disinfection byproduct (DBP) species. For ΔF/F values above the corresponding thresholds, the relative changes of fluorescence intensity were well correlated with the concentrations of individual DBP species such as trihalomethanes and haloacetonitriles. R2 values for CHBr3, CHBr2Cl and CHBrCl2 formed in DO seawater were 0.83, 0.80 and 0.68, respectively while for CS seawater, the corresponding R2 values were 0.91, 0.93 and 0.92. The presented data demonstrate that the intrinsic chemistry of DBP formation and dissolved organic matter (DOM) halogenation in seawater can be well quantified based on the examination of changes of its fluorescence. This approach can also be employed for practical monitoring of changes of properties of marine DOM and generation of DBPs in desalination, marine aquaculture and other processes.

The contribution of atmospheric particulate matter to the formation of CX3R-type disinfection by-products in rainwater during chlorination

Atmospheric particulate matter (PM) can be scavenged by rainfall and contribute dissolved organic matter (DOM) to rainwater. Rainwater may serve as a part or the whole of drinking water sources, leading to the introduction of PM-derived DOM into drinking water. However, little information is available on the role of PM-derived DOM as a remarkable precursor of CX3R-type disinfection by-products (DBPs) in rainwater. In this study, samples were collected from ten occurrences of rainfall in Shanghai and batch experiments were executed to explore the contribution of PM-derived DOM to CX3R-type DBP formation in rainwater and to further understand some of unknowns regarding its characteristics. Results revealed that a part of PM was scavenged by rainfall and the scavenge performance was better for smaller PM. The formation potentials (FPs) of individual CX3R-type DBP were similar among size-isolated PM. TCM was predominant (around 0.5–4.5 μg-C/mg-C) and TCAA was the secondary (around 0.6–3.2 μg-C/mg-C) among all detectable CX3R-type DBPs. Based on the PM removal data and DBP FP results, the contribution of PM-derived DOM to CX3R-type DBP formation in rainwater was modeled. Furthermore, aromatic proteins and soluble microbial product-like compounds were found to be significant compositions, which were reported to be DBP precursors. And low molecular weight (< 10 kDa) DOM derived from total PM and rainwater exhibited higher CX3R-type DBP FPs. DOM fractions with higher SUVA254 and SUVA285 values gave relatively higher yields of CX3R-type DBPs, indicating that aromatic compounds played an important role in DBP formation.

Formation of disinfection by-products under influence of shale gas produced water

Accidental spills and surface discharges of shale gas produced water could contaminate water resources and generate health concerns. The study explored the formation and speciation of disinfection by-products (DBPs) during chlorination of natural waters under the influence of shale gas produced water. Results showed the presence of produced water as low as 0.005% changed the DBP profile measurably. A shift to a more bromine substitution direction for the formation of trihalomethanes, dihaloacetic acids, trihaloacetic acids, and dihaloacetonitriles was illustrated by exploring the individual DBP species levels, bromine substitution factors, and DBP species fractions, and the effect was attributable to the introduction of bromide from produced water. The ratio of dichloroacetic and trichloroacetic acids also increased, which was likely affected by different bromination degrees at elevated bromide concentrations. Increasing blend ratios of produced water enhanced the formation of DBPs, especially the brominated species, while such negative effects could be alleviated by pre-treating the produced water with ozone/air stripping to remove bromide. The study advances understandings about the impacts of produced water spills or surface discharges regarding potential violation of Stage 2 DBP rules at drinking water treatment facilities.

Hazard assessment of three haloacetic acids, as byproducts of water disinfection, in human urothelial cells

Disinfection by-products (DBPs) are compounds produced in the raw water disinfection processes. Although increased cancer incidence has been associated with exposure to this complex mixture, the carcinogenic potential of individual DBPs remains not well known; thus, further studies are required. Haloacetic acids (HAAs) constitute an important group among DBPs. In this study, we have assessed the in vitro carcinogenic potential of three HAAs namely chloro-, bromo-, and iodoacetic acids. Using a long-term (8 weeks) and sub-toxic doses exposure scenario, different in vitro transformation markers were evaluated using a human urothelial cell line (T24). Our results indicate that long-term exposure to low doses of HAAs did not reproduce the genotoxic effects observed in acute treatments, where oxidative DNA damage was induced. No changes in the transformation endpoints analyzed were observed, as implied by the absence of significant morphological, cell growth rate and anchorage-independent cell growth pattern modifications. Interestingly, HAA-long-term exposed cells developed resistance to oxidative stress damage, what would explain the observed differences between acute and long-term exposure conditions. Accordingly, data obtained under long-term exposure to sub-toxic doses of HAAs could be more accurate, in terms of risk assessment, than under acute exposure scenarios.

Use of differential absorbance to estimate concentrations of chlorinated disinfection by-product in drinking water: Critical review and research needs

ABSTRACTDifferential UV absorbance (ΔA) has been proposed as a method for estimating disinfection by-products (DBP) concentrations in drinking water at a lower cost and at higher frequencies than the sampling programs required by regulations. Various equations developed in laboratory settings between individual DBP concentrations and ΔA272 have been reported in the literature. Although the form of the DBP–ΔA relationships (linear or exponential) is shared by most published studies, the fitting parameters vary and must be calibrated for each site. This is usually explained by differences in the nature of the natural organic matter (NOM) reacting with free chlorine. This literature review suggests that future research should first focus on improving our understanding of the reaction between NOM moieties and chlorine, and its impact on UV absorbance spectra, and second on overcoming the challenges of applying ΔA for estimating DBPs in full-scale facilities.

In vitro studies on the tumorigenic potential of the halonitromethanes trichloronitromethane and bromonitromethane

Epidemiological data indicate that chronic exposure to water disinfection by-products (DBPs) may result in increased risk of cancer. However, the real carcinogenic potential of individual DBPs is not well known. In this study, we assessed the in vitro carcinogenic potential of trichloronitromethane (TCNM) and bromonitromethane (BNM), two halonitromethanes (HNMs) commonly found in DBPs' mixtures at comparably high concentrations. Human lung BEAS-2B cells were exposed for 8weeks to TCNM and BNM, and the acquisition of different in vitro cancer-like features was evaluated. The results indicate that long-term exposure to non-cytotoxic doses of TCNM and BNM did not cause carcinogenic transformation as indicated by the absence of morphological changes, no effects on cell growth, no changes in the level of matrix metalloproteinases (MMPs) secretion, and no increased anchorage-independent cell growth capacity. Furthermore, TCNM- and BNM-exposed BEAS-2B cells were unable to enhance tumour growth directly or by indirect influence of the surrounding stroma. Our results indicate that the carcinogenic effects of DBP mixtures cannot be attributed to the evaluated HNMs. This is the first study evaluating the cell transformation effects of TCNM and BNM under a long-term exposure scenario using suitable hallmarks of the cancer process.

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.

Method to assess component contribution to toxicity of complex mixtures: Assessment of puberty acquisition in rats exposed to disinfection byproducts

A method based on regression modeling was developed to discern the contribution of component chemicals to the toxicity of highly complex, environmentally realistic mixtures of disinfection byproducts (DBPs). Chemical disinfection of drinking water forms DBP mixtures. Because of concerns about possible reproductive and developmental toxicity, a whole mixture (WM) of DBPs produced by chlorination of a water concentrate was administered as drinking water to Sprague–Dawley (S–D) rats in a multigenerational study. Age of puberty acquisition, i.e., preputial separation (PPS) and vaginal opening (VO), was examined in male and female offspring, respectively. When compared to controls, a slight, but statistically significant delay in puberty acquisition was observed in females but not in males. WM-induced differences in the age at puberty acquisition were compared to those reported in S–D rats administered either a defined mixture (DM) of nine regulated DBPs or individual DBPs. Regression models were developed using individual animal data on age at PPS or VO from the DM study. Puberty acquisition data reported in the WM and individual DBP studies were then compared with the DM models. The delay in puberty acquisition observed in the WM-treated female rats could not be distinguished from delays predicted by the DM regression model, suggesting that the nine regulated DBPs in the DM might account for much of the delay observed in the WM. This method is applicable to mixtures of other types of chemicals and other endpoints.