Disinfection By-products In Water Research Articles

Formation of disinfection byproducts during chlorination of mixed nitrogenous compounds in swimming pools

Disinfection byproducts (DBPs) in swimming pool waters are receiving increasing attention because of their toxicity and widespread occurrence. Current studies rarely investigate the formation of DBPs from typical precursors in swimming pools under mixed exposure. They also rarely investigate the formation of carbonaceous DBPs (C-DBPs) and nitrogenous DBPs (N-DBPs) simultaneously. In this study, the formation of C-DBPs and N-DBPs were investigated during chlorination of mixed precursors (i.e., tryptophan, urea, creatinine, and ammonia). The effects of precursors and operation parameters were also investigated. Among the four precursors, tryptophan had the highest DBP formation potential. Urea and ammonia restrained the formation of C-DBPs but promoted the formation of more toxic N-DBPs. C-DBP yields were significantly higher than N-DBP yields under all experimental conditions. Longer reaction time and higher chlorine dosage promoted the formation of C-DBPs, while higher temperature decreased the concentration of N-DBPs. The presence of bromide not only improved the sum yields of DBPs, but also shifted chlorinated DBPs to brominated species.

Analysis of the Kinetics of Swimming Pool Water Reaction in Analytical Device Reproducing Its Circulation on a Small Scale.

The most common cause of diseases in swimming pools is the lack of sanitary control of water quality; water may contain microbiological and chemical contaminants. Among the people most at risk of infection are children, pregnant women, and immunocompromised people. The origin of the problem is a need to develop a system that can predict the formation of chlorine water disinfection by-products, such as trihalomethanes (THMs). THMs are volatile organic compounds from the group of alkyl halides, carcinogenic, mutagenic, teratogenic, and bioaccumulating. Long-term exposure, even to low concentrations of THM in water and air, may result in damage to the liver, kidneys, thyroid gland, or nervous system. This article focuses on analysis of the kinetics of swimming pool water reaction in analytical device reproducing its circulation on a small scale. The designed and constructed analytical device is based on the SIMATIC S7-1200 PLC driver of SIEMENS Company. The HMI KPT panel of SIEMENS Company enables monitoring the process and control individual elements of device. Value of the reaction rate constant of free chlorine decomposition gives us qualitative information about water quality, it is also strictly connected to the kinetics of the reaction. Based on the experiment results, the value of reaction rate constant was determined as a linear change of the natural logarithm of free chlorine concentration over time. The experimental value of activation energy based on the directional coefficient is equal to 76.0 . These results indicate that changing water temperature does not cause any changes in the reaction rate, while it still affects the value of the reaction rate constant. Using the analytical device, it is possible to constantly monitor the values of reaction rate constant and activation energy, which can be used to develop a new way to assess pool water quality.

Comparison of chlorination and chloramination practices on microbial inactivation efficiencies within a scaled‐up water distribution network using central composite design

AbstractDisinfection practices reduce the incidence of water‐borne diseases but may result in formation of disinfection byproducts (DBPs) in raw water that are reported to be carcinogenic. Central composite design (CCD) was employed in the present study for optimization of disinfectant dose and contact time with the rationale to evaluate if an optimal balance could be achieved between minimal DBPs formation and effective microbial inactivation with either free or combined chlorine in treated water within a lab‐scale prototype network to simulate real water distribution network conditions. After a series of experimental runs based upon design of experiments (DoE) by CCD, dose was found to be the most significant factor (P < 0.01) in determining DBPs formation in both disinfectant’s applications. Where, contact time significantly (P < 0.01) affected bacterial inactivation in chlorination experiments, in contrast, dose was effective in chloramination experiments. Thus, it was concluded that the optimal balance may be achieved in the water networks with the help of multifactorial optimization when disinfectant dose was maintained near 3 mg/L as applied chlorine dose in both disinfection cases, while contact time was 62 and 155 min for chlorine and chloramine, respectively.

The Alleviative Effect of Vitamin B2 on Potassium Bromate-Induced Hepatotoxicity in Male Rats.

Potassium bromate (PB) is a food enhancer, water disinfection by-product, and a proven carcinogen. It elicits toxicities in the living organism due to exposure and in a dose-dependent manner. The present study discourses the ameliorative efficacy of riboflavin (RF) in PB-administered rodents. The animals were distributed into five treatment groups: control (group I), PB alone (group II, 150 mg/kg), RF alone (group III, 2 mg/kg), PB+RF1 (group IV, 150 mg/kg + 2 mg/kg), and PB+RF2 (group V, 150 mg/kg + 4 mg/kg). After the round of the treatment, the animals were sacrificed to collect their blood and liver samples for the detailed analysis. Group II depicted perturbed liver functions evidenced by altered serum and toxicity markers along with the disturbed redox balance. Also, these biochemical results were found harmonious with histopathological analysis and comet assay. However, group III showed no noticeable alteration in the same parameters, whereas the combination groups (IV and V) exhibited dose-dependent amelioration in the PB-induced toxicities. Interestingly, RF favored apoptosis concomitant with suppressing the necrosis in the PB-challenged groups, as shown by the activity of caspase-3 and lactate dehydrogenase. Histopathological analysis and comet assay further consolidate these results. Hence, RF has significant alleviative property against PB-induced hepatotoxicity in vivo that can be used in the consumer items containing the toxicant.

Degradation of aliphatic halogenated contaminants in water by UVA/Cu–TiO2 and UVA/TiO2 photocatalytic processes: Structure-activity relationship and role of reactive species

This study investigated the degradation of eight aliphatic halogenated contaminants (one brominated flame retardant and seven disinfection by-products) in synthetic drinking water by the UVA/TiO2 and UVA/Cu–TiO2 processes. The degradation rate constants of 2,2-bis(bromomethyl)-1,3-propanediol and trichloromethane in the UVA/Cu–TiO2 process were 10.1 and 1.29 times, respectively, higher than those in the UVA/TiO2 process. In contrast, the degradation rate constants of dichloroacetaldehyde, monochloroacetonitrile, monobromoacetonitrile and dibromonitromethane in the UVA/Cu–TiO2 process were 8.15, 2.33, 2.84 and 1.80 times, respectively, lower than those in the UVA/TiO2 process. The degradation rate constants of monobromonitromethane and dichloronitromethane were comparable in the two processes. The relationships between the degradation rate constants and the structural characteristics of the selected contaminants were examined to explain the different degradation efficacies of the contaminants in the two processes. As suggested by a quantitative structure-activity relationship (QSAR) model, the UVA/TiO2 process favored the degradation of contaminants with more polar electron-withdrawing moieties and higher degrees of chlorination. While the UVA/Cu–TiO2 process favored the degradation of hydrophilic unsaturated contaminants with multiple bonds. The concentrations of the reactive species (e.g., HO and e−) generated in the two photocatalytic processes were quantified using competition kinetics. The UVA/Cu–TiO2 process generated >10 times higher concentrations of HO than the UVA/TiO2 process, suggesting that the former process was more suitable for the degradation of contaminants that are reactive towards HO, while e− and e−-derived superoxide radicals were non-negligible contributors to contaminant degradation in the UVA/TiO2 process.

Chemopreventive effect of riboflavin on the potassium bromate-induced renal toxicity in vivo.

Potassium bromate (PB) is a general food additive, flavor enhancer, a by-product of water disinfection, and a class 2 carcinogen. It exerts various toxic effects in a dose- and time-dependent manner in vivo. This study is to explore the chemopreventive efficacy of vitamin B2 (riboflavin, RF) in PB-administered Swiss albino rats. The rats were distributed into five groups: control (group 1), PB alone (group 2, 150mg/kg), RF alone (group 3, 2mg/kg), PB + RF1 (group 4, 150 and 2mg/kg), and PB + RF2 (group 5, 150 and 4mg/kg). All the rodents were sacrificed after the completion of the treatment cycle. Then, blood and kidney samples were subjected to biochemical analysis. Group 2 demonstrated vivid signs of renal toxicities evidenced by altered renal function markers (urea, creatinine, albumin, glutathione-S-transferase) and redox status parameters (superoxide dismutase, catalase, glutathione reductase, reduced glutathione, lipid, and protein oxidation products). However, group 3 exhibited a slight alteration in many of the parameters while groups 4 and 5 demonstrated dose-dependent chemopreventive efficiency of RF against PB-induced alterations. Besides, RF seemed to facilitate apoptosis as well as inhibition of the necrosis in the PB-pre-challenged groups, as demonstrated by the cleaved PARP and lactate dehydrogenase activity. Also, the histopathological analysis and comet assay validate the biochemical results of the treatment groups significantly. All these results plead that RF has a significant chemopreventive property against PB-induced toxicity in vivo. Therefore, RF is a suitable agent in preventing the PB-induced toxicities at the clinical and industrial levels.

Associations of urinary dichloroacetic acid and trichloroacetic acid exposure with platelet indices: Exploring the mediating role of blood pressure in the general population

Human exposure to drinking water disinfection by-products (DBPs) is potentially linked to high blood pressure (BP), which may be associated with abnormal platelet activation. This study investigated whether the relationship between DBP exposure with platelet change was mediated by BP. DBP biomarkers, such as urinary dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), BP and platelet indices from 505 adults from a hospital in Shijiazhuang, China were measured. The cross-sectional associations among DCAA and TCAA exposure, BP and platelet indices were explored through multivariable linear regressions, and the mediation effect of BP was evaluated using the Sobel–Goodman test. We observed that DCAA and TCAA were positively associated with systolic BP (all p for trends < 0.01), which was positively associated with platelet count (PLC) (p for trend < 0.05). Mediation analysis indicated that systolic BP fully mediated the associations of DCAA and TCAA with PLC. When BP was controlled, a previously inverse significant relation between DCAA and platelet distribution width (PDW) remained significant (p < 0.05). Obtained results suggested that exposure to DCAA may contribute to decreased PDW in humans. Systolic BP is a possible mediator of the association between DCAA exposure and PLC. TCAA may indirectly positively affect PLC by increasing systolic BP.

Toxicological assessment of seven unregulated drinking water Disinfection By-products (DBPs) using the zebrafish embryo bioassay

Disinfection By-products (DBPs) are formed during the chemical treatment of water for human consumption, by the reaction of raw water with chemical agents used in the different steps of the process. Disinfection is one of the most important steps, inactivating pathogens and preventing their regrowth during water distribution. However, it is also involved in DBPs formation due to the use of disinfectant agents, such as chlorine, which reacts with dissolved precursors, such as pharmaceuticals, toxins, pesticides, among others. Given their widespread occurrence, potential human health and (eco) toxicological impacts are of particular interest due to their potential carcinogenicity and various non-carcinogenic effects, such as endocrine disruption. In this study, the developmental toxicity of chemically- different unregulated DBPs was evaluated using zebrafish embryo bioassay. Embryos were exposed to different concentrations of the target DBPs and multiple endpoints, including, mortality, morphological abnormalities and locomotor behavior were assessed at specific developmental stages (24, 48, 72 and 96 hpf). The different families of DBPs tested included nitrosamines, aldehydes, alcohols and ketones. The results show that the effects were compound dependent, with EC10 values varying between 0.04 mg/L (2-ethyl-1-hexanal) to 9.2 mg/L (hexachloroacetone). Globally, several of the tested unregulated DBPs displayed higher toxicity when compared with the available data for some already regulated, such as trihalomethanes (THMs), which highlights the importance of screening the toxicity of still untested and poorly characterized DBPs.

The impact of nutrition and lifestyle on male fertility.

Male unexplained infertility has long been suspected to result from environmental, lifestyle and nutritional factors. However, the literature on the subject is still scarce, and clinical studies providing robust evidence are even scarcer. In addition, some similar studies come to different conclusions. Dietary pattern can influence spermatogenesis by its content of fatty acids and antioxidants. Yet, in an age of industrialized mass food production, human bodies become more exposed to the ingestion of xenobiotics, as well as chemicals used for production, preservation, transportation and taste enhancement of foods. We attempted in this paper to collect the available evidence to date on the effect of nutritional components on male fertility. A systematic search of the relevant literature published in PubMed, ScienceDirect and Cochrane Central Register of Controlled Trials Database was conducted. Literature was evaluated according to the Newcastle-Ottawa- Scale. Epidemiological observations are concordant in demonstrating an association of low-quality sperm parameters with higher intake of red meat, processed and organ meat and fullfat dairy. On the contrary, better semen parameters were observed in subjects consuming a healthy diet, rich in fruit, vegetables, whole grains and fish. Evidences of the negative impact on male fertility of by-products of water disinfection, accumulation in food chain of persistent organochlorine pollutants, pesticides, phthalates from food and water containers and hormones used in breeding cattle have been reported. Clinical trials of the effects of micronutrients on semen parameters and outcomes of assisted fertilization are encouraging, although optimal modality of treatment should be established. Although quality of evidence should be ameliorated, it emerges that environmental factors can influence male fertility. Some nutrients may enhance fertility whereas others will worsen it. With diagnostic analysis on a molecular or even sub-molecular level, new interactions with micronutrients or molecular components of our daily ingested foods and leisure drugs may lead to a better understanding of so far suspected but as yet unexplained effects on male spermatogenesis and fertility.

Comparative Quantitative Toxicology and QSAR Modeling of the Haloacetonitriles: Forcing Agents of Water Disinfection Byproduct Toxicity.

The haloacetonitriles (HANs) is an emerging class of nitrogenous-disinfection byproducts (N-DBPs) present in disinfected drinking, recycled, processed wastewaters, and reuse waters. HANs were identified as primary forcing agents that accounted for DBP-associated toxicity. We evaluated the toxic characteristics of iodoacetonitrile (IAN), bromoacetonitrile (BAN), dibromoacetonitrile (DBAN), bromochloroacetonitrile (BCAN), tribromoacetonitrile (TBAN), chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), bromodichloroacetonitrile (BDCAN), and chlorodibromoacetonitrile (CDBAN). This research generated the first quantitative, comparative analyses on the mammalian cell cytotoxicity, genotoxicity and thiol reactivity of these HANs. The descending rank order for HAN cytotoxicity was TBAN ≈ DBAN > BAN ≈ IAN > BCAN ≈ CDBAN > BDCAN > DCAN ≈ CAN ≈ TCAN. The rank order for genotoxicity was IAN ≈ TBAN ≈ DBAN > BAN > CDBAN ≈ BDCAN ≈ BCAN ≈ CAN ≈ TCAN ≈ DCAN. The rank order for thiol reactivity was TBAN > BDCAN ≈ CDBAN > DBAN > BCAN > BAN ≈ IAN > TCAN. These toxicity metrics were associated with membrane permeability and chemical reactivity. Based on their physiochemical parameters and toxicity metrics, we developed optimized, robust quantitative structure activity relationship (QSAR) models for cytotoxicity and for genotoxicity. These models can predict cytotoxicity and genotoxicity of novel HANs prior to analytical biological evaluation.

The identification of halogenated disinfection by-products in tap water using liquid chromatography–high resolution mass spectrometry

In this paper, a comprehensive method for the identification of the unknown halogenated DBPs (X-DBPs, X = Cl, Br, and I) in the tap water of Wuhan, China via liquid chromatography-high resolution mass spectrometry (LC-HRMS) was developed. 123 X-DBPs were identified through the stepwise procedure, 94 of them were newly identified, and 3 of them were confirmed by standards. Most X-DBPs were aliphatic compounds and highly unsaturated and phenolic compounds, some X-DBPs contained multiple halogen atoms and rich in carboxyl groups, such as C2H2O2BrCl, C2H2O2Br2, and C2H2O2ClI. It was worth noting that the concentration of some X-DBPs had the same trend with time. Most Cl-DBPs remained stable and I-DBPs were detected occasionally by monitoring the change of concentration of these X-DPBs with the time during three consecutive months. The results demonstrate that the proposed method could provide valuable molecular formula and structure information on unknown multiple halogenated DBPs, or be used for the identification of other multiple halogenated organic compounds in different media.

Disinfection Byproducts in Swimming Pool Water and Its Impact, Method for Sanitization

Disinfection Byproducts in Swimming Pool Water and Its Impact, Method for Sanitization

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years’ post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year’s initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH4+/NH3), and specific ultraviolet absorbance (SUVA254) were significantly higher (67 ± 40%, 418 ± 125%, 192 ± 120%, and 31 ± 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br−) concentrations (up to 8.7 μM]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (≤1 year).

Microplastics release precursors of chlorinated and brominated disinfection byproducts in water

Microplastics (MPs) are prevalent global pollutants that are being detected in aquatic ecosystems and drinking water sources around the world. In addition to plastic polymers, MPs contain various chemical substances (known as “additives”) that can leach and risk water quality. In this paper, we investigated for the first time the potential release of disinfection byproducts (DBPs) precursors when MPs are exposed to hydrolysis and/or degradation by simulated sunlight. Seventeen MPs with seven different polymer types were collected either as commercial products (e.g. drinking water bottles, shopping bags, recycled plastics, etc.) or pure/virgin polymers. Results showed high release of dissolved organic carbon (DOC) from five MP samples and a significant increase in bromide concentrations from four MPs. DBPs formation potential (DBPFP) experiments with MPs’ leachates showed higher concentrations of chlorinated trihalomethanes (THMs), haloacetonitriles (HANs), and total organic halogens (TOX) in three samples, while a significant shift to brominated DBPs was observed in samples containing bromide. Extending the leaching experiments to four consecutive cycles showed that the leaching of DOC and DBPs’ precursor significantly decreased after the second leaching cycle. Further analysis revealed that the reactivity of the leached DOC – indicated by THMFP yields – was comparable to those of several raw waters that supply drinking water treatment plants. The leached THMs and TOX from MPs that were exposed to UVA irradiation were in general higher than MPs that were run under dark conditions.

AWWA Water Science Author Spotlight

Laboratory Simulation of Postfire Effects on Conventional Drinking Water Treatment and Disinfection Byproduct Formation Amanda K. Hohner, R. Scott Summers, and Fernando L. Rosario-Ortiz My research group evaluates the effects of extreme events and watershed disturbances on the resilience of drinking water systems. We study how events such as wildfire, floods, and droughts affect source water quality and treatment process performance, and how utilities can best adapt to address these disruptions in water quality. Our research was motivated by the needs of water utilities across North America, but especially utilities in the West that have experienced wildfires or are concerned about the risk of future wildfires to their water treatment system. The rise in wildfire activity has created new and unknown risks to source water quality, and there was a lack of scientific knowledge of the postfire impacts on treatment processes. Our goal was to develop a systematic approach to understand the effects of forest floor heating on water quality and treatment and to provide guidance to utilities that are vulnerable to wildfire. Amanda (Mandi) pauses with her dog, Holly, during a hike to Ice Lake in the Wallowa Mountains in northeast Oregon. I love spending time hiking and camping in forest watersheds. In the Pacific Northwest and in Colorado, we are fortunate to rely on these forest watersheds for high-quality drinking water supplies. When driving or hiking in wilderness areas, you often come across areas that have burned, and I want to understand how these drastic changes and visible changes affect downstream communities. With climate-change-related wildfires and other extreme weather events becoming more frequent, it will be increasingly important for water utilities to be prepared to adapt to climatic impacts. Our research in AWWA Water Science is a step toward understanding the potential risk of wildfire to water treatment and finished water quality. Our goal is to influence how water utilities and regulators are investing their resources as they now have to prepare for more uncertainty and greater variability in source water quality. I grew up in the state of Washington and have always lived out West, where there is a focus on the importance of water resources. Watching the effects of climate change through the rise in wildfire activity in areas that haven't burned historically—like the western Cascades—truly highlights the rapid changes and challenges we face as a scientific community. Adapting to consequences of climate change within the drinking water community will only become more important in the coming years. For fun and to clear my head, we like to spend time outdoors, hiking and running with our pup. In the winter, we cross-country ski around where we live, and in the summer we head to the lake to do stand-up paddle boarding. To learn more about this research, see the abstract on page 25 of the December issue of Journal AWWA and visit the article, available online at https://doi.org/10.1002/aws2.1155.

Disinfection By-Product Exposures and the Risk of Musculoskeletal Birth Defects.

Epidemiological studies suggest that exposure to water disinfection by-products (DBPs) may increase the risk of certain birth defects. However, evidence for musculoskeletal defects (MSDs) is limited. Previous MSD studies have not examined DBPs beyond trihalomethanes (THMs) and have not separately examined limb or diaphragm defects which may have distinct developmental etiologies. We calculated adjusted odds ratios (aORs) in a registry-based case-control study of birth defects in Massachusetts with complete quarterly 1999-2004 data on four THMs and five haloacetic acids (HAAs). We matched 10 controls each to 187 MSD cases based on week of conception. Weight-averaged town-level first-trimester DBP exposures were individually assigned based on residence at birth. We adjusted THM models for exposure to the sum of five HAAs (HAA5), and HAA models for the sum of four THMs (THM4). We detected positive exposure-response associations for all grouped MSDs with THM4 quintiles (aOR range: 1.90-3.18) and chloroform quartiles (aOR range: 1.30-2.21), and for reduction of upper or lower limbs with chloroform quartiles (aOR range: 2.39-3.52). We detected elevated aORs for diaphragmatic hernia with DBP9 (sum of THM4 and HAA5), and chloroform and bromodichloromethane tertiles and an exposure-response relationship for THM4 tertiles (aOR range: 1.67-1.80). This is the first epidemiological study to examine HAAs in relation to MSDs. Given the indirect nature of our exposure assessment data and small case numbers, the exposure-response relationships that we detected for THM4 and chloroform warrant further investigation.

Formation of disinfection by-products in the swimming pool water treated with different disinfection types

Formation of disinfection by-products in the swimming pool water treated with different disinfection types

Halogenated semivolatile acetonitriles as chloramination disinfection by-products in water treatment: a new formation pathway from activated aromatic compounds.

The use of monochloramine as an alternative disinfectant to chlorine in drinking water treatment can lead to increased formation of emerging nitrogenous halogenated disinfection by-products (DBPs), even when the formation of regulated halogenated DBPs has decreased. In this study, we investigated formation of the semivolatile haloacetonitriles (HANs) from model nitrogen-containing compounds (6 amines, 1 amide, 6 amino acids, and 2 nitrogen-containing aromatic chemicals) and natural organic matter (NOM) reference materials after chloramination. In agreement with previous studies, most amino acids formed dichloroacetonitrile (DCAN). Additionally, DCAN formed from two amines containing aromatic rings (N,N-dimethylaniline and 3-(dimethylamino-methyl)indole) and the two nitrogen-containing aromatic chemicals (cotinine and phenytoin). This is the first report of DCAN formation from these precursors. DCAN also formed after chloramination of NOM reference materials, with the highest formation from the NOM material with the highest aromaticity. The results provide new evidence of a DCAN formation pathway from cleavage of activated aromatic structures after electrophilic substitution of chlorine and addition of monochloramine to the ring system. In particular, the results suggest that the previously proposed aldehyde pathway from the amino acid group is not responsible for the majority of DCAN formation from amino acids with an activated aromatic ring system. This newly proposed formation pathway for DCAN from activated aromatic organic matter has significant implications for NOM removal during water treatment to minimise DBP formation. Studies using 15N-labelled monochloramine showed that there was significant incorporation of nitrogen from monochloramine into DCAN, demonstrating that monochloramine disinfection promotes the formation of HANs.

Mixture effects of drinking water disinfection by-products: implications for risk assessment

Disinfection by-products (DBPs) in drinking water have been associated with increased cancer risk but effects of known DBPs cannot explain the mixture effects of disinfected water samples.

New Perspectives for Cancer Hazard Evaluation by the Report on Carcinogens: A Case Study Using Read-Across Methods in the Evaluation of Haloacetic Acids Found as Water Disinfection By-Products

Background: Due to the large number of chemicals not yet tested for carcinogenicity but to which people are exposed, the limited number of human and animal cancer studies conducted each year, and the frequent need for a timely response, mechanistic data are playing an increasingly important role in carcinogen hazard identification.Objectives:To provide a targeted approach to identify relevant mechanistic data in our cancer evaluation of haloacetic acids (HAAs), we used several approaches including systematic review, the 10 key characteristics of carcinogens (KCs), and read-across methods. Our objective in this commentary is to discuss the strengths, limitations, and challenges of these approaches in a cancer hazard assessment.Methods:A cancer hazard assessment for 13 HAAs found as water disinfection by-products was conducted. Literature searches for mechanistic studies focused on the KCs and individual HAAs. Studies were screened for relevance and categorized by KCs and other relevant data, including chemical properties, toxicokinetics, and biological effects other than KCs. Mechanistic data were organized using the KCs, and strength of evidence was evaluated; this information informed potential modes of action (MOAs) and read-across-like approaches. Three read-across options were considered: evaluating HAAs as a class, as subclass(es), or as individual HAAs (analog approach).Discussion:Because of data limitations and uncertainties, listing as a class or subclass(es) was ruled out, and an analog approach was used. Two brominated HAAs were identified as target (untested) chemicals based on their metabolism and similarity to source (tested) chemicals. In addition, four HAAs with animal cancer data had sufficient evidence for potential listing in the Report on Carcinogens (RoC). This is the first time that the KCs and other relevant data, in combination with read-across principles, were used to support a recommendation to list chemicals in the RoC that did not have animal cancer data. https://doi.org/10.1289/EHP5672