Disinfection by-products in drinking water and colorectal cancer: a meta-analysis

Better Together: Tandem Mass Spectrometry Achieves up to 50 Times Lower Quantification of 62 Disinfection Byproducts in Drinking Water

Disinfection byproducts (DBPs) are ubiquitous contaminants present in nearly all drinking water and are associated with adverse health effects in human epidemiologic studies. The most toxic DBPs are unregulated and often occur at concentrations well below regulated DBPs; thus, quantification at low parts-per-trillion (ng/L) levels is critical in assessing exposure. We developed a new liquid-liquid extraction-gas chromatography-tandem mass spectrometry (LLE-GC-MS/MS) method with the first analysis by tandem gas chromatography-mass spectrometry of 23 priority unregulated DBPs including 13 haloacetamides, 3 haloacetic acids, 2 haloacetonitriles, 1 haloacetaldehyde, 2 haloketones, and 2 halonitromethanes. When combined with our previous GC-MS/MS method for haloacetic acids and previously reported MS/MS transitions that we optimized for this method, the analysis of 62 regulated and priority unregulated DBPs at lower quantification limits is achieved. Limits of quantification for most DBPs were between 5 and 30 ng/L with r2 > 0.99 and an average of 9 times lower limits of quantification (LOQs) compared to LLE-GC-MS using selected ion monitoring (SIM). Relative standard deviations ranged from 0.7 to 30% for 61 DBPs in spiked samples. This new method was validated using tap waters from four US cities, where individual DBP concentrations ranged from 5 to 126,882 ng/L. This project provides the most comprehensive GC-MS/MS method for DBP analysis to date and is capable of analyzing volatile and semivolatile DBPs across nine different compound classes, including a class not previously analyzed by GC-MS/MS.

Chronic exposure to drinking water nitrate and trihalomethanes in the French CONSTANCES cohort

Trihalomethanes (THMs) and nitrate are widespread chemicals in drinking water. Chronic exposure has been associated with increased cancer risk despite inconclusive evidence, partly due to the challenges in long-term exposure assessment and potential exposure misclassification. We estimated concentrations of nitrate and THMs in drinking water using a public regulatory monitoring database (SISE-Eaux) for CONSTANCES, a French population-based prospective cohort. We obtained 26,322,366 measurements of drinking water parameters from 2000 to 2020. We excluded missing, implausible and duplicated measurements; we corrected or imputed missing geocodes of sampling locations; we calculated the annual median concentration of nitrate and THMs by surveillance area. To predict missing annual median concentrations, linear mixed models with random intercept using surveillance area as a clustering variable were developed for each region for nitrate and the four THM components (chloroform, chlorodibromomethane, bromodichloromethane and bromoform) separately. Concentrations in the nearest surveillance area from the household were merged per year among 75,462 participants with residential history geocoded for 2000-2020. Estimated concentrations resulting from this approach were compared with measured concentrations in 100 samples collected in Paris, Rennes and Saint-Brieuc in 2021. Median annual concentrations of total THMs and nitrate at study participants' homes for 2000-2020 were, respectively, 15.7 μg/l (IQR: 15.2) and 15.2 mg/l (IQR: 20.8). Among these, 35% were based on measurements for nitrate (16% for THMs), 44% (46%) were predicted using on linear mixed models, and 21% (38%) were based on distribution unit median values. Conditional R2 predictive models ranged from 0.71 to 0.91 (median: 0.85) for nitrate, and from 0.48 to 0.80 for THMs (median: 0.68). These concentrations will allow future association analyses with risk of breast and colorectal cancer. Our cleaning process introduced here could be adapted to other large drinking water monitoring data.

Comprehensive Toxicological Assessment of Halobenzoquinones in Drinking Water at Environmentally Relevant Concentration

Halobenzoquinones (HBQs), an emerging unregulated category of disinfection byproduct (DBP) in drinking water, have aroused an increasing concern over their potential health risks. However, the chronic toxicity of HBQs at environmentally relevant concentrations remains largely unknown. Here, the occurrence and concentrations of 13 HBQs in drinking water from a northern megacity in China were examined using ultrahigh performance liquid chromatography coupled with triple-quadrupole tandem mass spectrometry (UHPLC-MS/MS). Four HBQs, including 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), 2,3,6-trichloro-1,4-benzoquinone (TriCBQ), and 2,5-dibromo-1,4-benzoquinone (2,5-DBBQ), were detected beyond 50% occurrence frequency and at median concentrations from 4 to 50 ng/L. The chronic toxicity of these four HBQs to normal human colon and liver cells (FHC and THLE-2) was investigated at these concentrations. After 90 days of exposure, 2,5-DBBQ and 2,6-DCBQ induced the highest levels of oxidative stress and deoxyribonucleic acid (DNA) damage in colon and liver cells, respectively. Moreover, 2,5-DBBQ and 2,6-DCBQ were also found to induce epithelial-mesenchymal transition (EMT) in normal human liver cells via the extracellular signal regulated kinase (ERK) signaling pathway. Importantly, heating to 100 °C (boiling) was found to efficiently reduce the levels of these four HBQs in drinking water. These results suggested that environmentally relevant concentrations of HBQs could induce cytotoxicity and genotoxicity in normal human cells, and boiling is a highly efficient way of detoxification for HBQs.

Mammalian Cell Genotoxicity of Potable Reuse and Conventional Drinking Waters

Potable reuse water is increasingly part of the water supply portfolio for municipalities facing water shortages, and toxicity assays can be useful for evaluating potable reuse water quality. We examined the Chinese hamster ovary cell acute direct genotoxicity of potable reuse waters contributed by disinfection byproducts (DBPs) and anthropogenic contaminants and used the local conventional drinking waters as benchmarks for evaluating potable reuse water quality. Our results showed that treatment trains based on reverse osmosis (RO) were more effective than RO-free treatment trains for reducing the genotoxicity of influent wastewaters. RO-treated reuse waters were less genotoxic than the local tap water derived from surface water, whereas reuse waters not treated by RO were similarly genotoxic as the local drinking waters when frequent replacement of granular activated carbon limited contaminant breakthrough. The genotoxicity contributed by nonvolatile, uncharacterized DBPs and anthropogenic contaminants accounted for ≥73% of the total genotoxicity. The (semi)volatile DBPs of current research interest contributed 2-27% toward the total genotoxicity, with unregulated DBPs being more important genotoxicity drivers than regulated DBPs. Our results underscore the need to look beyond known, (semi)volatile DBPs and the importance of determining whole water toxicity when assessing the quality of disinfected waters.

Low Parts Per Trillion Detection of Iodinated Disinfection Byproducts in Drinking Water and Urine using Vacuum-Assisted Sorbent Extraction and GC-MS/MS

Disinfection byproducts (DBPs) are ubiquitous environmental contaminants, which are present in virtually all drinking water and linked to detrimental health effects. Iodinated-DBPs are more cytotoxic and genotoxic than chloro- and bromo-DBPs and are formed during disinfection of iodide-containing source water. Liquid-liquid extraction (LLE) paired with gas chromatography (GC)-mass spectrometry (MS) has been the method of choice in the study of low molecular weight iodinated-DBPs; however, this method is laborious and time-consuming and struggles with complex matrices. We developed an environmentally friendly method utilizing headspace solid phase extraction with the application of vacuum to measure six iodinated-trihalomethanes (I-THMs) in drinking water and urine. Vacuum-assisted sorbent extraction (VASE) has the ability to exhaustively and rapidly extract volatile and semivolatile compounds from liquid matrices without the use of solvent. Using VASE with GC-MS/MS provides improved analyte recovery and reduced matrix interference compared to LLE. Additionally, VASE enables extraction of 30 samples simultaneously with minimal sample handling and improved method reproducibility. Using VASE with GC-MS/MS, we achieved quantification limits of 3-4 ng/L. This technique was demonstrated on drinking water from four cities, where five I-THMs were quantified at levels 10-33 times below comparable LLE methods with 10 times lower volumes of sample (10 mL vs 100 mL).

From Theory to Practice: Leveraging Chemical Principles To Improve the Performance of Peroxydisulfate-Based In Situ Chemical Oxidation of Organic Contaminants

In situ chemical oxidation (ISCO) using peroxydisulfate has become more popular in the remediation of soils and shallow groundwater contaminated with organic chemicals. Researchers have studied the chemistry of peroxydisulfate and the oxidative species produced upon its decomposition (i.e., sulfate radical and hydroxyl radical) for over five decades, describing reaction kinetics, mechanisms, and product formation in great detail. However, if this information is to be useful to practitioners seeking to optimize the use of peroxydisulfate in the remediation of hazardous waste sites, the relevant conditions of high oxidant concentrations and the presence of minerals and solutes that affect radical chain reactions must be considered. The objectives of this Review are to provide insights into the chemistry of peroxydisulfate-based ISCO that can enable more efficient operation of these systems and to identify research needed to improve understanding of system performance. By gaining a deeper understanding of the underlying chemistry of these complex systems, it may be possible to improve the design and operation of peroxydisulfate-based ISCO remediation systems.

Total organic halogen (TOX) in drinking water: Occurrence, correlation analysis, and precursor removal during drinking water treatment

Total organic halogen (TOX) in drinking water provides a measurement of the overall organic halogenated disinfection by-products (DBPs) formed during disinfection. Yangtze River Delta is one of the regions with the highest population density, the fastest urbanization process, and the most severe water pollution in China. Collecting water samples from full-scale drinking water treatment plants (DWTPs) in this region, this study firstly surveyed TOX occurrence in drinking water. Besides, the correlation of TOX formation potential (TOXFP) and trihalomethane formation potential (THMFP) with general water quality parameters (e.g., dissolved organic carbon [DOC], UV254, and specific ultraviolet absorbance) and the removal efficiencies of TOX precursors by different water treatment processes were also investigated. TOX levels in DWTP effluents (i.e., finished water) ranged from 29 to 165 μg/L (median 67 μg/L), and those in simulated distribution system waters ranged from 101 to 276 μg/L (median 158 μg/L). There were generally higher linear regression coefficient values for raw water (R2 = 0.51-0.88) than for treated water (R2 = 0.33-0.64) in terms of the relationship between DBP formation potentials and general parameters. However, a relatively stronger correlation between THMFP and TOXFP was observed for treated water (R2 = 0.80, p < 0.001) than for raw water (R2 = 0.64, p < 0.001). The overall treatment efficiencies of investigated parameters in DWTPs generally followed the order of UV254 > DOC > TOX precursors > THM precursors. Notably, the overall removal rates of DOC and TOX precursors in summer (averaging 59 % and 54 %, respectively) were obviously higher than those in winter (averaging 39 % and 38 %, respectively), which was assumed to be related to the seasonal variation of bioactivity in sand filter. These results could expand the knowledge of TOX in drinking water, and provide valuable perspectives to water industry and DBP research.

Disinfection by-products in drinking water and risk of colorectal cancer: a population-based cohort study

BACKGROUND

Colorectal cancer is the third most common malignancy worldwide and is strongly linked to lifestyle and environmental risk factors. Although several drinking-water disinfection by-products are confirmed rodent carcinogens, the evidence in humans for carcinogenicity associated with these by-products, including colorectal cancer, is still inconclusive.

METHODS

We assessed the association of long-term exposure to trihalomethanes (THMs), the most prevalent disinfection by-products in chlorinated drinking water, with incidence of colorectal cancer in 58 672 men and women in 2 population-based cohorts. Exposure was assessed by combining long-term information of residential history with drinking water-monitoring data. Participants were categorized according to no exposure, low exposure (<15 µg/L), and high exposure (≥15 µg/L). Incident cases of colorectal cancer were ascertained by use of the Swedish National Cancer Register.

RESULTS

During an average follow-up of 16.8 years (988 144 person-years), 1913 cases of colorectal cancer were ascertained (1176 cases in men and 746 in women, respectively). High THM concentrations in drinking water (≥15 µg/L) were associated with increased risk of colorectal cancer in men (hazard ratio = 1.26, 95% confidence interval = 1.05-1.51) compared with no exposure. When subsites were assessed, the association was statistically significant for proximal colon cancer (hazard ratio = 1.59, 95% confidence interval = 1.11 to 2.27) but not for distal colon cancer or rectal cancer. In women, we observed overall no association of THMs with colorectal cancer.

CONCLUSION

These results add further evidence that disinfection by-products in drinking water may be a possible risk factor for proximal colon cancer in men. This observation was made at THM concentrations lower than those in most previous studies.

Metabolomic Signatures of Exposure to Nitrate and Trihalomethanes in Drinking Water and Colorectal Cancer Risk in a Spanish Multicentric Study (MCC-Spain)

We investigated the metabolomic profile associated with exposure to trihalomethanes (THMs) and nitrate in drinking water and with colorectal cancer risk in 296 cases and 295 controls from the Multi Case-Control Spain project. Untargeted metabolomic analysis was conducted in blood samples using ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. A variety of univariate and multivariate association analyses were conducted after data quality control, normalization, and imputation. Linear regression and partial least-squares analyses were conducted for chloroform, brominated THMs, total THMs, and nitrate among controls and for case-control status, together with a N-integration model discriminating colorectal cancer cases from controls through interrogation of correlations between the exposure variables and the metabolomic features. Results revealed a total of 568 metabolomic features associated with at least one water contaminant or colorectal cancer. Annotated metabolites and pathway analysis suggest a number of pathways as potentially involved in the link between exposure to these water contaminants and colorectal cancer, including nicotinamide, cytochrome P-450, and tyrosine metabolism. These findings provide insights into the underlying biological mechanisms and potential biomarkers associated with water contaminant exposure and colorectal cancer risk. Further research in this area is needed to better understand the causal relationship and the public health implications.

Polystyrene may alter the cooperation mechanism of gut microbiota and immune system through co-exposure with DCBQ

The toxicity of Polystyrene (PS) may be higher through co-exposure with other pollutants. Human can simultaneously face the challenges from the various pollutants. Nevertheless, little research has been done on the combined effects of PS and 2,6-dichloro-p-benzoquinone (DCBQ) disinfection byproduct. Considering the potential risk of PS and DCBQ, we aimed to illustrate the effects of PS in combination with DCBQ on the immune responses of mice. We found that cotreatment of DCBQ and PS may inhibit the activity of spleen CD4+ T cells and interfere with the normal function of the immune system. Further research found that DCBQ + PS resulted in increasing amount of the inflammatory cells in intestine via histopathological evaluation. The reason might be that DCBQ + PS has changed the composition of intestinal flora, abnormally activated intestinal macrophage, and inhibited the expression of immune-related genes, thus leading to intestinal immune disorders and triggering intestinal inflammation. In summary, PS may alter the cooperation mechanism of gut microbiota and immune system through co-exposure with DCBQ. Current results suggested that more attention should be paid to the combined toxic effects of environmental contaminants.

Bromoform exposure is associated with non-melanoma skin cancer: evidence from NHANES 2011-2020

Background

Non-melanoma skin cancer (NMSC) is a prevalent skin malignancy. It has been indicated in many studies that trihalomethanes (THMs) exposure has a strong association with tumors but has not been associated with NMSC. Our investigation aims to explore the association between THMs exposure and NMSC.

Methods

Cross-sectional data from the 2011 to 2020 National Health and Nutrition Examination Survey (NHANES) was collected. Poisson regression and subgroup analyses were performed to evaluate the association between individual THMs components and NMSC. Fitted smoothing curves and generalized additive models were also used.

Results

This study involved 5,715 individuals, 98 (1.7%) of whom self-reported NMSC. After adjusting for covariates, Poisson regression showed that higher blood TBM levels were associated with an increased likelihood of NMSC (OR = 1.03; 95% CI: 1.01-1.05, p = 0.002). However, the correlation between the blood levels of TCM, DBCM, and BDCM and the likelihood of NMSC was not statistically significant (all p > 0.05). Subgroup analysis and interaction tests showed no significant differences between blood TBM concentration and the likelihood of NMSC, indicating that age, gender, and race were significantly independent of this positive association (all p < 0.05).

Conclusions

Our results implied that among adults older than 65 years old in the U.S., elevated blood TBM concentrations were positively associated with NMSC. More prospective investigations are required to validate this relationship with the early prevention of NMSC.

Cytotoxicity Comparison between Drinking Water Treated by Chlorination with Postchloramination versus Granular Activated Carbon (GAC) with Postchlorination

Granular activated carbon treatment with postchlorination (GAC/Cl2) and chlorination followed by chloramination (Cl2/NH2Cl) represent two options for utilities to reduce DBP formation in drinking water. To compare the total cytotoxicity of waters treated by a pilot-scale GAC treatment system with postchlorination (and in some instances with prechlorination upstream of GAC (i.e., (Cl2)/GAC/Cl2)) and chlorination/chloramination (Cl2/NH2Cl) at ambient and elevated Br- and I- levels and at three different GAC ages, we applied the Chinese hamster ovary (CHO) cell cytotoxicity assay to whole-water extracts in conjunction with calculations of the cytotoxicity contributed by the 33 (semi)volatile DBPs lost during extractions. At both ambient and elevated Br- and I- levels, GAC/Cl2 and Cl2/NH2Cl achieved comparable reductions in the formation of regulated trihalomethanes (THMs) and haloacetic acids (HAAs). Nonetheless, GAC/Cl2 always resulted in lower total cytotoxicity than Cl2/NH2Cl, even at up to 65% total organic carbon breakthrough. Prechlorination formed (semi)volatile DBPs that were removed by the GAC, yet there was no substantial difference in total cytotoxicity between Cl2/GAC/Cl2 and GAC/Cl2. The poorly characterized fraction of DBPs captured by the bioassay dominated the total cytotoxicity when the source water contained ambient levels of Br- and I-. When the water was spiked with Br- and I-, the known, unregulated (semi)volatile DBPs and the uncharacterized fraction of DBPs were comparable contributors to total cytotoxicity; the contributions of regulated THMs and HAAs were comparatively minor.

Zerovalent Iron/Cu Combined Degradation of Halogenated Disinfection Byproducts and Quantitative Structure-Activity Relationship Modeling

Previous studies have reported that zerovalent iron (ZVI) can reduce several aliphatic groups of disinfection byproducts (DBPs) (e.g., haloacetic acids and haloacetamides) effectively, and the removal efficiency can be significantly improved by metallic copper. Information regarding ZVI/Cu combined degradation of different types of halogenated DBPs can help understand the fate of overall DBPs in drinking water distribution and storage systems consisting of unlined cast iron/copper pipes and related potential control strategies. In this study, we found that, besides aliphatic DBPs, many groups of new emerging aromatic DBPs formed in chlorinated and chloraminated drinking water can be effectively degraded by ZVI/Cu; meanwhile, total organic halogen and total ion intensity were reduced significantly after treatment. Moreover, a robust quantitative structure-activity relationship model was developed and validated based on the ZVI/Cu combined degradation rate constants of 14 typical aromatic DBPs; it can predict the degradation rate constants of other aromatic DBPs for screening and comparative purposes, and the optimized descriptors indicate that DBPs possessing a lower value of the lowest unoccupied molecular orbital energy and a higher value of dipole moment tend to present higher degradation rate constants. In addition, toxicity data of 47 DBPs (belonging to 18 groups) were predicted by two previously established toxicity models, demonstrating that, although most DBPs exhibit higher toxicity than their dehalogenated products, some DBPs show lower toxicity than their lowly halogenated analogs.

Algae impacted drinking water: Does switching to chloramination produce safer drinking water?

Harmful algal (cyanobacterial) blooms (HABs) are increasing throughout the world. HABs can be a direct source of toxins in freshwater sources, and associated algal organic matter (AOM) can act as precursors for the formation of disinfection by-products (DBPs) in drinking water. This study investigated the impacts of algae on DBP formation using treatment with chloramine, which has become a popular disinfectant in the U.S. and in several other countries because it can significantly lower the levels of regulated DBPs formed. Controlled laboratory chloraminations were conducted using live field-collected algal biomass dominated by either Phormidium sp. or Microseira wollei (formerly known as Lyngbya wollei) collected from Lake Wateree and Lake Marion, SC. Sixty-six priority, unregulated or regulated DBPs were quantified using gas chromatography (GC)-mass spectrometry (MS). The presence of HAB-dominated microbial communities in source waters led to significant increases in more toxic nitrogen-containing DBPs (1.5-5 fold) relative to lake waters collected in HAB-free waters. Compared to chlorinated Phormidium-impacted waters, chloraminated waters yielded lower total DBP levels (up to 123 μg/L vs. 586 μg/L for low Br^-/I^- waters), but produced a greater number of brominated, iodinated, and mixed halogenated DBPs in high Br^-/I^- waters. Among the DBPs formed in Phormidium-impacted chloraminated waters, dichloroacetic acid, trichloromethane, chloroacetic acid, chloropropanone, and dichloroacetamide were dominant. For Microseira wollei-impacted chloraminated waters, total DBP concentrations ranged from 33 to 145 μg/L (approximately 3-5 times lower than chlorination), with dichloroacetic acid, dichloroacetamide, and trichloromethane dominant. Overall, chloramination significantly reduced calculated cytotoxicity and genotoxicity in low Br^- and I^- waters, but produced 1.3 fold higher calculated cytotoxicity (compared to chlorine) with high Br^-/I^- waters due to increased formation of more toxic iodo- and mixed halogenated DBPs.

Enhanced selectivity for acidic contaminants in drinking water: From suspect screening to toxicity prediction

A novel analytical workflow for suspect screening of organic acidic contaminants in drinking water is presented, featuring selective extraction by silica-based strong anion-exchange solid-phase extraction, mixed-mode liquid chromatography-high resolution accurate mass spectrometry (LC-HRMS), peak detection, feature reduction and compound identification. The novel use of an ammonium bicarbonate-based elution solvent extended strong anion-exchange solid-phase extraction applicability to LC-HRMS of strong acids. This approach performed with consistently higher recovery and repeatability (88 ± 7 % at 500 ng L^-1), improved selectivity and lower matrix interference (mean = 12 %) over a generic mixed-mode weak anion exchange SPE method. In addition, a novel filter for reducing full-scan features from fulvic and humic acids was successfully introduced, reducing workload and potential for false positives. The workflow was then applied to 10 London municipal drinking water samples, revealing the presence of 22 confirmed and 37 tentatively identified substances. Several poorly investigated and potentially harmful compounds were found which included halogenated hydroxy-cyclopentene-diones and dibromomethanesulfonic acid. Some of these compounds have been reported as mutagenic in test systems and thus their presence here requires further investigation. Overall, this approach demonstrated that employing selective extraction improved detection and helped shortlist suspects and potentially toxic chemical contaminants with higher confidence.

Chlorination disinfection by-products in Southeast Asia: A review on potential precursor, formation, toxicity assessment, and removal technologies

This review discusses disinfection by-products' (DBPs) potential precursors, formation, and toxicity, alongside available research on the treatment of DBPs in Southeast Asian countries' water sources. Although natural organic matter (NOM) in the form of humic and fulvic acids is the major precursor of DBPs formation, the presence of anthropogenic organic matter (AOM) also plays essential roles during disinfection using chlorine. NOM has been observed in water sources in Southeast Asian countries, with a relatively high concentration in peat-influenced water sources and a relatively low concentration in non-peat-influenced water sources. Similarly, AOMs, such as microplastics, pharmaceuticals, pesticides, and endocrine-disrupting chemicals (EDCs), have also been detected in water sources in Southeast Asian countries. Although studies regarding DBPs in Southeast Asian countries are available, they focus on regulated DBPs. Here, the formation potential of unregulated DBPs is also discussed. In addition, the toxicity associated with extreme DBPs' formation potential, as well as the effectiveness of treatments such as conventional coagulation, filtration, adsorption, and ozonation in reducing DBPs' formation potential in Southeast Asian sources of water, is also analyzed.

Quantitative structure-toxicity relationships of halobenzoquinone isomers on DNA reactivity and genotoxicity

Halobenzoquinones (HBQs) are an emerging class of drinking water disinfection byproducts that have been predicted as bladder carcinogens. However, data on the genotoxicity of HBQs are still scarce. This study performed a quantitative structure-toxicity relationship (QSTR) analysis of HBQ isomers on DNA reactivity and genotoxicity. The interaction of HBQs with calf thymus DNA (ct-DNA) was studied using multi-spectroscopic and molecular docking techniques. UV-Vis absorption spectra observed a significant hyperchromic effect with the increase of HBQ concentration. The fluorescence intensity of both probe-ct-DNA decreased with the increasing concentration of HBQs, indicating that the interaction mode between each HBQs and DNA was quite complicated, and there were both minor groove binding and intercalation binding. Molecular docking showed that HBQs interacted with DNA predominantly via hydrogen bond at guanine-rich areas in the minor groove of DNA. The genotoxicity of HBQs on human hepatocytes (L-02) was evaluated by micronucleus test, and the results showed that HBQs could cause significant chromosomal damage. The rank order of HBQ isomers on DNA reactivity and genotoxicity was 2,5-HBQs > their corresponding 2,6-HBQs. QSTR analysis found that dipole moment is the key structural descriptor influencing both DNA reactivity and genotoxicity of HBQ isomers. This study suggested that HBQs have caused genotoxicity which was influenced by their isomeric effects, warranting a comprehensive understanding of the genotoxic and carcinogenic risks associated with HBQs exposure.

Occurrence of brominated disinfection by-products in thermal spas

Thermal spas are gaining more and more popularity among the population because they are used for recreational purposes. Disinfecting these baths without losing the health benefits poses a challenge for swimming pool operators. Previous studies have mainly focused on regulated chlorinated DBPs in freshwater pools with no bromide or seawater pools with very high bromide content. Thermal water pools have a low bromide content and in combination with chlorine can lead to chlorinated, brominated and mixed halogenated DBP species. The occurrence of brominated and mixed halogenated DBPs in these types of pools is largely unexplored, with very few or limited studies published on regulated DBPs and even fewer on emerging DBP classes. In the field of swimming pool water disinfection, apart from extensive studies in the field of drinking water disinfection, only a few studies are known in which >39 halogenated and 16 non-halogenated disinfection by-products, including regulated trihalomethanes (THM) and haloacetic acids (HAA), were investigated in swimming pool water. Calculated bromine incorporation factor (BIF) demonstrated that even small amounts of bromide in swimming pool water can lead to a large shift in DBP species towards brominated and mixed halogenated DBPs. Dihaloacetonitriles (DHANs) accounted for >50% of the calculated cytotoxicity and genotoxicity on average. Comparison of the target analysis with the TOX showed that a major part of the measured TOX (69% on average) could be explained by the regulated classes THMs, HAAs, and the unregulated class of HANs. This study aims to help operators of swimming pools with bromide-containing water to gain a better understanding of DBP formation in future monitoring and to fill the knowledge gap that has existed so far on the occurrence of DBPs in thermal water pools.

Estimating National Exposures and Potential Bladder Cancer Cases Associated with Chlorination DBPs in U.S. Drinking Water

BACKGROUND

Disinfection byproducts (DBPs) in public water systems (PWS) are an unintended consequence resulting from reactions between mostly chlorine-based disinfectants and organic and inorganic compounds in source waters. Epidemiology studies have shown that exposure to DBP (specifically trihalomethanes) was associated with an increased risk of bladder cancer.

OBJECTIVE

Our goal was to characterize the relative differences in exposures and estimated potential bladder cancer risks for people served by different strata of PWS in the United States and to evaluate uncertainties associated with these estimates.

METHODS

We stratified PWS by source water type (surface vs. groundwater) and population served (large, medium, and small) and calculated population-weighted mean trihalomethane-4 (THM4) concentrations for each stratum. For each stratum, we calculated a population attributable risk (PAR) for bladder cancer using odds ratios derived from published pooled epidemiology estimates as a function of the mean THM4 concentration and the fraction of the total U.S. population served by each stratum of systems. We then applied the stratum-specific PARs to the total annual number of new bladder cancer cases in the U.S. population to estimate bladder cancer incidence in each stratum.

RESULTS

Our results show that approximately 8,000 of the 79,000 annual bladder cancer cases in the United States were potentially attributable to DBPs in drinking water systems. The estimated attributable cases vary based on source water type and system size. Approximately 74% of the estimated attributable cases were from surface water systems serving populations of > 10,000 people. We also identified several uncertainties that may affect the results from this study, primarily related to the use of THM4 as a surrogate measure for DBPs relevant to bladder cancer.

DISCUSSION

Despite significant reductions in exposure over the past several decades, our study suggests that ∼ 10 % of the bladder cancer cases in the United States may still be attributed to exposure to DBPs found in drinking water systems. https://doi.org/10.1289/EHP9985.

Effects of operating conditions on disinfection by-product formation, calculated toxicity, and changes in organic matter structures during seawater chlorination

This study systematically quantified the impacts of different operation conditions, e.g., pH, chlorine dosages, contact times, and temperatures towards the disinfection by-product (DBP) formation, integrated toxicity, and structural changes in seawater natural organic matter during seawater chlorination. Higher concentrations of total DBPs were found under longer contact times, higher chlorine dosages, higher temperatures, and lower pH. The concentration of tribromomethane, the most abundant DBP, was found lowest at pH 10. Monobromoacetic acid, dibromoacetonitrile, and dibromoacetaldehyde were the three main contributors to integrated cyto- and geno-toxicity, stressing the need to monitor DBPs based on their contributions to integrated toxicity, regardless they are regulated or nonregulated. The concentrations of total organic chlorine remained stable under different conditions, while those of total organic bromine increased with increasing contact times, chlorine dosages, and temperatures, but with decreasing pH, indicating the changes of toxicity in chlorinated seawater compared to drinking water or groundwater. Changes of ultraviolet absorbance at 254 nm and fluorescence excitation emission matrix values are useful indicators for monitoring the concentrations of high molecular weight adsorbable organic bromine and total organic halogen under all operating conditions.

The antiestrogen-like activity and reproductive toxicity of 2,6-DCBQ on female zebrafish upon sub-chronic exposure

2,6-Dichloro-1,4-benzoquinone (2,6-DCBQ), an emerging water disinfection by-product, is widely detected in water resources. However, its potential effects on the reproductive system are largely unknown. Here, we investigated the long-term effects of 2,6-DCBQ on gonadal development by exposing zebrafish from 15 to 180 days postfertilization (dpf). Following exposure to 2,6-DCBQ (20 and 100 µg/L), female-specific effects including delayed puberty onset, retarded ovarian growth and breakdown of the zona radiata were observed, resulting in subfertility in adult females. Adverse effects in folliculogenesis disappeared two months after cessation of 2,6-DCBQ administration. In contrast, no adverse impacts were noted in male testes. The effects on females were associated with significant reduction in 17β-estradiol (E2) level, suggesting a role for 2,6-DCBQ in anti-estrogenic activity. E2 level change in blood was further supported by dysregulated expression of genes (cyp19a1a, fshb, kiss3, esr2b, vtg1, and vtg3) related to the hypothalamic-pituitary-gonad-liver (HPGL) axis. The present study demonstrates for the first time that 2,6-DCBQ induces reproductive impairments in female zebrafish through disrupting 17β-estradiol level.

Feel the Burn: Disinfection Byproduct Formation and Cytotoxicity during Chlorine Burn Events

Nitrification and biofilm growth within distribution systems remain major issues for drinking water treatment plants utilizing chloramine disinfection. Many chloraminated plants periodically switch to chlorine disinfection for several weeks to mitigate these issues, known as "chlorine burns". The evaluation of disinfection byproduct (DBP) formation during chlorine burns beyond regulated DBPs is scarce. Here, we quantified an extensive suite of 80 regulated and emerging, unregulated DBPs from 10 DBP classes in drinking water from two U.S. drinking water plants during chlorine burn and chloramination treatments. Total organic halogen (TOX), including total organic chlorine, total organic bromine, and total organic iodine, was also quantified, and mammalian cell cytotoxicity of whole water mixtures was assessed in chlorine burn waters for the first time. TOX and most DBPs increased in concentration during chlorine burns, and one emerging DBP, trichloroacetaldehyde, reached 99 μg/L. THMs and HAAs reached concentrations of 249 and 271 μg/L, respectively. Two highly cytotoxic nitrogenous DBP classes, haloacetamides and haloacetonitriles, increased during chlorine burns, reaching up to 14.2 and 19.3 μg/L, respectively. Cytotoxicity did not always increase from chloramine treatment to chlorine burn, but a 100% increase in cytotoxicity was observed for one plant. These data highlight that consumer DBP exposure during chlorine burns can be substantial.

Microseira wollei and Phormidium algae more than doubles DBP concentrations and calculated toxicity in drinking water

Warm weather and excess nutrients from agricultural runoff trigger harmful algal blooms, which can affect drinking water safety due to the presence of algal toxins and the formation of disinfection by-products (DBPs) during drinking water treatment. In this study, 66 priority, unregulated and regulated DBPs were quantified in chlorinated controlled laboratory reactions of harmful algae Microseira wollei (formerly known as Lyngbya wollei) and Phormidium using gas chromatography (GC)-mass spectrometry (MS). Live algae samples collected from algae-impacted lakes in South Carolina were chlorinated in both ultrapure water and real source waters containing natural organic matter. DBPs were also measured in finished water from a real drinking water plant impacted by a Microseira bloom. Results show that the presence of Microseira and Phormidium more than doubles total concentrations of DBPs formed by chlorination, with levels up to 586 μg/L formed in natural lake waters. Toxic nitrogen-containing DBPs also more than doubled in concentration, with levels up to 36.1, 3.6, and 37.9 μg/L for haloacetamides, halonitromethanes, and haloacetonitriles, respectively. In ultrapure water, DBPs also formed up to 314 μg/L when algae was chlorinated, demonstrating their ability to serve as direct precursors for these DBPs. When environmentally relevant levels of bromide and iodide were added to chlorination reactions, total DBPs increased 144, 51, and 24% for drinking water reservoir, Lake Marion and Lake Wateree Microseira respectively and 29% for Phormidium. Iodo-DBPs, bromochloroiodomethane, chloroiodoacetic acid, bromoiodoacetic acid, and diiodoacetic acid were observed in finished water from a drinking water plant impacted by Microseira, and bromochloroiodomethane and dibromoiodomethane were observed in chlorinated ultrapure water containing algae, bromide, and iodide. Notably, total calculated cytotoxicity tripled in Microseira-impacted waters and doubled for Phormidium-impacted waters. Calculated genotoxicity doubled for Microseira-impacted waters and more than doubled in Phormidium-impacted waters. Haloacetonitriles were major drivers of calculated cytotoxicity in algae-impacted waters, while haloacetic acids were major drivers of calculated genotoxicity in algae-impacted waters. These results provide the most extensive assessment of DBPs formed from chlorination of algae-impacted waters and highlight potential impacts to drinking water and human health. Results from this study are particularly applicable to drinking water treatment plants that employ pre-chlorination, which can cause the release of algal organic matter (AOM) precursors to form DBPs.

Halogen substitution reactions of halobenzenes during water disinfection

Although being successfully applied all over the world for more than 100 years water disinfection by means of chlorination possesses certain drawbacks, first of all formation of hazardous disinfection by-products (DBP). Aromatic halogenated DBPs significantly contribute to the total organic halogen and developmental toxicity of chlorinated water. The present study deals with investigation of possible substitution of one halogen for another in aromatic substrates in conditions of aqueous chlorination/bromination. The reaction showed high yields especially in case of substrates with proper position of an activating group in the aromatic ring. Thus, ipso-substitution of iodine by chlorine is the main process of aqueous chlorination of para-iodoanisole. Oxidation of the eliminating I⁺ ions into non-reactive IO₃^- species facilitates the substitution. Oxidation of eliminating Br⁺ is not so easy while being highly reactive it attacks initial substrates forming polybrominated products. Substitution of iodine and bromine by chlorine may also involve migration of electrophilic species inside the aromatic ring resulting in larger number of isomeric DBPs. Substitution of chlorine by bromine in aromatic substrates during aqueous bromination is not so pronounced as substitution of bromine by chlorine in aqueous chlorination due to higher electronegativity of chlorine atom. However, formation of some chlorine-free polybrominated products proves possibility of that process.

Modeling the formation of trihalomethanes in rural and semi-urban drinking water distribution networks of Costa Rica

Chlorination is one of the most important stages in the treatment of drinking water due to its effectiveness in the inactivation of pathogenic organisms. However, the reaction between chlorine and natural organic matter (NOM) generates harmful disinfection by-products (DBPs), such as trihalomethanes (THMs). In this research, drinking water quality data was collected from the distribution networks of 19 rural and semi-urban systems that use water sources as springs, surfaces, and a mixture of both, in three provinces of Costa Rica from April 2018 to September 2019. Twelve models were developed from four data sets: all water sources, spring, surface, and a mixture of spring and surface waters. Linear, logarithmic, and exponential multivariate regression models were developed for each data set to predict the concentration of total trihalomethanes (TTHMs) in the distribution networks. Concentrations of TTHMs were found between < 0.20 and 91.31 µg/L, with chloroform being the dominant species accounting for 62% of TTHMs on average. Turbidity, free residual chlorine, total organic carbon (TOC), dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV₂₅₄) showed a significant correlation with TTHMs. In all the data sets the linear models presented the best goodness-of-fit and were moderately robust. Four models, the best of each data set, were validated with data from the same systems, and, according to the criteria of R², standard error (SE), mean square error (MSE), and mean absolute error (MAE), spring water and mixed spring/surface water models showed a satisfactory level of explanation of the variability of the data. Moreover, the models seem to better predict TTHM concentrations below 30 µg/L. These models were satisfactory and could be useful for decision-making in drinking water supply systems.

Drinking Water Source, Chlorinated Water, and Colorectal Cancer: A Matched Case-Control Study in Ethiopia

BACKGROUND

There is no study conducted on the association between disinfection byproducts (DBPs) in chlorinated drinking water and colorectal cancer (CRC) in Ethiopia. Therefore, this study aimed to determine the relation between chlorine based DBPs in drinking water and CRC in Addis Ababa, Ethiopia.

METHODS

A facility based matched case control study was conducted involving 224 cases and 448 population controls from June 2020 to May 2021. Cases were defined as histologically confirmed CRC cases. Cases were matched with controls by residence, age, and sex using frequency and individual matching. Geocoding of cases, health facility, and georeferencing of controls were carried out. Data was collected using a pretested structured questionnaire. Pearson Chi square and Fisher's exact tests were employed to assess associations. Stratified analysis was used to detect confounding factors and effect modification. A multivariable conditional logistic regression was used to identify risk factors of CRC.

RESULTS

Of 214 CRC cases, 148 (69.2%) used chlorinated water whereas out of 428 controls 161 (37.6%) used chlorinated water. In the final regression model, drinking chlorinated surface water (adjusted matched odds ratio [adjusted mOR] = 2.6; 95% CI 1.7-4.0), history of swimming (adjusted mOR = 2.4; 95% CI 1.4-4.1), years at the place of current residence (adjusted mOR = 1.5; 95% CI 1.1-2.2), hot tap water use for showering (adjusted mOR; 3.8 = 95% CI 2.5-5.9) were significantly associated with CRC. The stratified analysis confirmed that smoking and meat ingestion were not effect modifiers and confounders.

CONCLUSION

Drinking chlorinated water for extended years is a significant risk factor for CRC in Addis Ababa, Ethiopia. In addition, hot tap water use for showering, and swimming history are risk factors for CRC. This information is essential to design integrated interventions that consider chlorination by-products and exposure routes toward the prevention and control of CRC in Ethiopia. Initiating alternative methods to chlorine disinfection of drinking water is also essential.

Exposure to widespread drinking water chemicals, blood inflammation markers, and colorectal cancer

BACKGROUND

Trihalomethanes (THMs) and nitrate are widespread chemicals in drinking water associated with colorectal cancer risk but mechanisms are not well understood.

OBJECTIVES

We explored the association between exposure to THMs and nitrate in drinking water and inflammation markers, and the link with colorectal cancer risk.

METHODS

A subset of 198 colorectal cancer cases and 205 controls from the multicase-control study MCC-Spain were included. Average concentration of THMs (chloroform, bromodichloromethane, dibromochloromethane, bromoform) and nitrate in tap water at the residence was estimated from age 18 until 2 years before the interview ("long term") and for a recent period (3 years before diagnosis). Serum levels of EGF, eotaxin, G-CSF, IL-17E, IL-1rA, IL-8, IP-10, MDC, MPO, periostin, VEGF, and C-reactive protein (CRP) were measured. We estimated the linear association between inflammation markers and exposure among controls, and the odds ratio of colorectal cancer associated with THM and nitrate exposure, and inflammation markers. A mediation analysis was conducted to identify inflammation markers in the pathway between THM/nitrate exposure and colorectal cancer.

RESULTS

Serum concentrations of EGF, IL-8, IL-17E and eotaxin increased with recent residential levels of brominated THMs, chloroforom and/or total THM. No associations were observed for nitrate and for long-term residential THM levels. All residential exposures except chloroform were positively associated with colorectal cancer. Serum concentrations of VEGF and periostin were positively associated with colorectal cancer, while EGF was inversely associated. One protein-exposure combination (periostin-recent ingested brominated THMs) slightly mediated the association with colorectal cancer risk.

DISCUSSION

Results suggest that estimated THM exposure is involved in inflammation processes. However, the study design was limited to stablish etiologically relevant associations between the protein levels and colorectal cancer risk. The lack of association between nitrate exposure and inflammation markers suggests other biological mechanisms are involved in the link with colorectal cancer.

Health effects of exposure to chlorination by-products in swimming pools

Concerns have been raised regarding the potential negative effects on human health of water disinfectants used in swimming pools. Among the disinfection options, the approaches using chlorine-based products have been typically preferred. Chlorine readily reacts with natural organic matter that are introduced in the water mainly through the bathers, leading to the formation of potentially harmful chlorination by-products (CBPs). The formation of CBPs is of particular concern since some have been epidemiologically associated with the development of various clinical manifestations. The higher the concentration of volatile CBPs in the water, the higher their concentration in the air above the pool, and different routes of exposure to chemicals in swimming pools (water ingestion, skin absorption, and inhalation) contribute to the individual exposome. Some CBPs may affect the respiratory and skin health of those who stay indoor for long periods, such as swimming instructors, pool staff, and competitive swimmers. Whether those who use chlorinated pools as customers, particularly children, may also be affected has been a matter of debate. In this article, we discuss the current evidence regarding the health effects of both acute and chronic exposures in different populations (work-related exposures, intensive sports, and recreational attendance) and identify the main recommendations and unmet needs for research in this area.

Disinfection Byproduct Recovery during Extraction and Concentration in Preparation for Chemical Analyses or Toxicity Assays

Over 700 disinfection byproducts (DBPs) have been identified, but they account for only ∼30% of total organic halogen (TOX). Extracting disinfected water is necessary to assess the overall toxicity of both known and unknown DBPs. Commonly used DBP extraction methods include liquid-liquid extraction (LLE) and solid-phase extraction (SPE), which may use either XAD resins or other polymeric sorbents. With few exceptions, DBP recoveries have not been quantified. We compared recoveries by LLE, XAD resins, and a mixture of Phenomenex Sepra SPE sorbents (hereafter SPE) for (semi-)volatile DBPs and nonvolatile model compounds at the 1-L scale. We scaled up the three methods to extract DBPs in 10 L of chlorinated creek waters. For (semi-)volatile DBPs, XAD resulted in lower recoveries than LLE and SPE at both 1- and 10-L scales. At the 10-L scale, recovery of certain trihalomethanes and trihalogenated haloacetic acids by XAD was negligible, while recovery of other (semi-)volatile DBPs extracted by XAD (<30%) was lower than by SPE or LLE (30-60%). TOX recovery at the 10-L scale was generally similar by the three extraction methods. The low TOX recovery (<30%) indicates that the toxicity assessed by bioassays predominantly reflects the contribution of the nonvolatile, hydrophobic fraction of DBPs.

Increased disinfection byproducts in the air resulting from intensified disinfection during the COVID-19 pandemic

Intensified use of disinfectants to control COVID-19 could unintentionally increase the disinfection byproducts (DBPs) in the environment. In indoor spaces, it is critical to determine the optimal disinfection practice to prevent the spread of the virus while keeping DBPs at relatively low levels in the air. The formation of DBPs exceed 0.1 μg/mg while hypochlorite dosed at >10 mg/m³. The total DBP concentrations in highly disinfected places (100-200 mg/m³ hypochlorite) were as high as 66.8 μg/m³, and the Hazard Index (HI) was up to 0.84, and both values were much higher than those in less disinfected places (<10 mg/m³ hypochlorite). Taking into account the HI, formation yields and the origin of the DBPs, we recommended 10 mg/m³ as the suggested hypochlorite dose to minimize DBPs generation during routine disinfection for controlling the coronavirus. DBPs in indoor air could be eliminated by ventilation, reducing the usage of personal care products, and wiping the solid surface with water before or after disinfection. These results highlighted the necessity to control air-borne DBPs and their associated health risks arising from intensified disinfection, and will guide the further development of evidence-based regulation on DBP exposure during disinfection and improve public health protection.

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.

Why We Will Continue to Lose Our Battle with Cancers If We Do Not Stop Their Triggers from Environmental Pollution

Besides our current health concerns due to COVID-19, cancer is a longer-lasting and even more dramatic pandemic that affects almost a third of the human population worldwide. Most of the emphasis on its causes has been posed on genetic predisposition, chance, and wrong lifestyles (mainly, obesity and smoking). Moreover, our medical weapons against cancers have not improved too much during the last century, although research is in progress. Once diagnosed with a malignant tumour, we still rely on surgery, radiotherapy, and chemotherapy. The main problem is that we have focused on fighting a difficult battle instead of preventing it by controlling its triggers. Quite the opposite, our knowledge of the links between environmental pollution and cancer has surged from the 1980s. Carcinogens in water, air, and soil have continued to accumulate disproportionally and grow in number and dose, bringing us to today's carnage. Here, a synthesis and critical review of the state of the knowledge of the links between cancer and environmental pollution in the three environmental compartments is provided, research gaps are briefly discussed, and some future directions are indicated. New evidence suggests that it is relevant to take into account not only the dose but also the time when we are exposed to carcinogens. The review ends by stressing that more dedication should be put into studying the environmental causes of cancers to prevent and avoid curing them, that the precautionary approach towards environmental pollutants must be much more reactionary, and that there is an urgent need to leave behind the outdated petrochemical-based industry and goods production.

Use of trihalomethanes as a surrogate for haloacetonitrile exposure introduces misclassification bias

Epidemiologists have used trihalomethanes (THMs) as a surrogate for overall disinfection byproduct (DBP) exposure based on the assumption that THM concentrations are proportional to concentrations of other DBP classes. Toxicological evidence indicates THMs are less potent toxins than unregulated classes like haloacetonitriles (HANs). If THMs are not proportional to the DBPs driving toxicity, the use of THMs to measure exposure may introduce non-trivial exposure misclassification bias in epidemiologic studies. This study developed statistical models to evaluate the covariance and proportionality of HAN and THM concentrations in a dataset featuring over 9500 measurements from 248 public water systems. THMs only explain ∼30% of the variance in HANs, whether the data is pooled in a classic linear regression or hierarchically grouped by water system in a multilevel linear regression. The 95% prediction interval on HANs for the median THM concentration exceeds the interquartile range of HANs. Mean HAN:THM ratios range from ∼2.4% to ∼80% across water systems, and varied with source water category, season, disinfectant sequence and distribution system location. The HAN:THM ratio was 265% higher in groundwater systems than in surface water systems and declined by ∼40% between finished effluent and maximum residence times in surface water systems with chlorine-chlorine disinfection. A maximum likelihood approach was used to estimate the misclassification bias that may result from using THMs to construct risk-ratios, assuming that HANs represent the "true" DBP exposure risk. The results indicate an odds ratio of ∼2 estimated with THM concentrations could correspond to a true odds ratio of 4-5. These findings demonstrate the need for epidemiologic studies to evaluate exposure by measuring DBPs that are likely to drive toxicity.

Meta-analysis of small for gestational age births and disinfection byproduct exposures

BACKGROUND

Some epidemiological studies show associations between disinfection byproducts (DBPs) and adverse developmental outcomes.

OBJECTIVES

We undertook a meta-analysis of epidemiological studies on maternal exposure to trihalomethanes (THMs) and haloacetic acids (HAAs) and risk of small for gestational age (SGA) birth.

METHODS

We identified forty-five publications including two reports and five theses via a 2020 literature search. Nineteen study populations from 16 publications met the inclusion criteria and were systematically evaluated. Effect measures were pooled using random effects meta-analytic methods along with cumulative, sub-group and meta-regression analyses to examine between-study heterogeneity and variation in risk across different DBP measures.

RESULTS

We detected a small increased risk for SGA with exposure to the sum of four (i.e., THM4) THM4 (odds ratio (OR) = 1.07; 95%CI: 1.03, 1.11), chloroform (OR = 1.05; 95%CI: 1.01, 1.08), bromodichloromethane (OR = 1.08; 95%CI: 1.05, 1.11) and the sum of the brominated THM4 (OR = 1.05; 95%CI: 1.02, 1.09). Larger ORs were detected for the sum of five haloacetic acids (i.e., HAA5) (OR = 1.12; 95%CI: 1.01, 1.25), dichloroacetic acid (OR = 1.25; 95%CI: 1.01, 1.41) and trichloroacetic acid (OR = 1.21; 95%CI: 1.07, 1.37). We detected larger SGA risks for several THM4 among the prospective cohort and case-control studies compared to retrospective cohorts and for the SGA3/5% (vs. SGA10%) studies. The THM4 meta-regression showed associations between SGA and the total quality score based on categorical or continuous measures. For example, an OR of 1.03 (95%CI: 1.01, 1.06) was detected for each 10-point increase in the study quality score based on our systematic review.

CONCLUSIONS

We detected a small increased risk of SGA based on 18 THM4 study populations that was comparable to a previous meta-analysis of eight THM4 study populations. We also found increased risks for other THM4 and HAA measures not previously examined; these results were robust after accounting for outliers, publication bias, type of SGA classification, different exposure windows, and other factors.

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.

Androgenic and Teratogenic Effects of Iodoacetic Acid Drinking Water Disinfection Byproduct in Vitro and in Vivo

Iodoacetic acid (IAA) is the most genotoxic iodinated disinfection byproduct known in drinking water. Previous studies have shown that IAA may be an endocrine disruptor. However, whether IAA has reproductive and developmental toxicity remains unclear. In this study, the reproductive and developmental toxicity of IAA was evaluated using a battery of in vitro and in vivo reproductive/developmental toxicity screening tests. The results of E-Screen, uterotrophic, and H295R steroidogenesis assays were negative. The Hershberger bioassay revealed that IAA could induce significant increases in absolute and relative weights of paired Cowper's glands. Moreover, there was an increasing trend in the relative weights of the ventral prostate. The micromass test showed that IAA could inhibit the differentiation of midbrain and limb bud cells. A reproductive/developmental toxicity screening test showed that IAA resulted in significantly increased relative weights of testis and seminal vesicles plus coagulating glands in parental male rats, with a dose-response relationship. IAA could not only induce head congestion in offspring but also decrease litter weight, viability index, and anogenital distance index of male pups on postnatal day 4. All these results indicated that IAA had reproductive and developmental toxicity.

Making Swimming Pools Safer: Does Copper-Silver Ionization with Chlorine Lower the Toxicity and Disinfection Byproduct Formation?

Swimming pools are commonly treated with chlorine, which reacts with the natural organic matter and organic matter introduced by swimmers and form disinfection byproducts (DBPs) that are associated with respiratory-related issues, including asthma, in avid swimmers. We investigated a complementary disinfectant to chlorine, copper-silver ionization (CSI), with the aim of lowering the amount of chlorine used in pools and limiting health risks from DBPs. We sampled an indoor and outdoor pool treated with CSI-chlorine during the swimming season in 2017-2018 and measured 71 DBPs, speciated total organic halogen, in vitro mammalian cell cytotoxicity, and N-acetyl-l-cysteine (NAC) thiol reactivity as a cytotoxicity predictor. Controlled, simulated swimming pools were also investigated. Emerging DBP concentrations decreased by as much as 80% and cytotoxicity decreased as much as 70% in the indoor pool when a lower chlorine residual (1.0 mg/L) and CSI was used. Some DBPs were quantified for the first time in pools, including chloroacetaldehyde (up to 10.6 μg/L), the most cytotoxic haloacetaldehyde studied to date and a major driver of the measured cytotoxicity in this study. Three highly toxic iodinated haloacetic acids (iodoacetic acid, bromoiodoacetic acid, and chloroiodoacetic acid) were also quantified in pools for the first time. We also found that the NAC thiol reactivity was significantly correlated to cytotoxicity, which could be useful for predicting the cytotoxicity of swimming pool waters in future studies.

Combination of high resolution mass spectrometry and a halogen extraction code to identify chlorinated disinfection byproducts formed from aromatic amino acids

Chlorination can lead to the formation of hazardous chlorinated disinfection byproducts (Cl-DBPs). We identified tyrosine (Tyr) and tryptophan (Trp) as precursors of toxic Cl-DBPs and developed a halogen extraction code to complement ultra performance liquid chromatography in tandem with high resolution mass spectrometry (UPLC-HRMS) in detecting and identifying Cl-DBPs. We detected 20 and 11 Cl-DBPs formed from chlorination of Tyr and Trp, respectively, and identified the structures of 15 Cl-DBPs. Fourteen structures were previously unreported. We also proposed the tentative formation pathways of these newly identified Cl-DBPs. Their incidence in real water sources demonstrated that these Cl-DBPs are likely to form during chlorination of reclaimed water. We computationally predicted the toxicity of these Cl-DBPs, which was relatively high, indicating that these Cl-DBPs could be hazardous and were of valid concern. Combining analytical data with the halogen extraction code can identify Cl-DBPs accurately from complex compounds. This analytical method can be used to identify Cl-DBPs of water treatment procedures in further studies.

Iodoacetic acid disrupts mouse oocyte maturation by inducing oxidative stress and spindle abnormalities

Disinfection by-products (DBPs) are compounds produced during the water disinfection process. Iodoacetic acid (IAA) is one of the unregulated DBPs in drinking water, with potent cytotoxicity and genotoxicity in animals. However, whether IAA has toxic effects on oocyte maturation remains unclear. Here, we show that IAA exposure resulted in metaphase I (MI) arrest and polar-body-extrusion failure in mouse oocytes, indicating that IAA had adverse effects on mouse oocyte maturation in vitro. Particularly, IAA treatment caused abnormal spindle assembly and chromosome misalignment. Previous studies reported that IAA is a known inducer of oxidative stress in non-germline cells. Correspondingly, we found that IAA exposure increased the reactive oxygen species (ROS) levels in oocytes in a dose-dependent manner, indicating IAA exposure could induce oxidative stress in oocytes. Simultaneously, DNA damage was also elevated in the nuclei of these IAA-exposed mouse oocytes, evidenced by increased γ-H2AX focus number. In addition, the un-arrested oocytes entered metaphase II (MII) with severe defects in spindle morphologies and chromosome alignment after 14-h IAA treatment. An antioxidant, N-acetyl-L-cysteine (NAC), reduced the elevated ROS level and restored the meiotic maturation in the IAA-exposed oocytes, which indicates that IAA-induced maturation failure in oocytes was mainly mediated by oxidative stress. Collectively, our results indicate that IAA exposure interfered with mouse oocyte maturation by elevating ROS levels, disrupting spindle assembly, inducing DNA damage, and causing MI arrest.

Covalent organic frameworks as an efficient adsorbent for controlling the formation of disinfection by-products (DBPs) in chlorinated drinking water

2,5-Dimethyl-p-phenylenediamine-1,3,5-triformylphloroglucinol covalent organic frameworks (PATP COF) were prepared and used as novel adsorbent for controlling the formation potential (FP) and reducing the toxic potential of both carbonaceous disinfection by-products (C-DBPs) and nitrogenous DBPs (N-DBPs) during their subsequent chlorination. During the PATP COF adsorption pretreatment process, the FP of C-DBPs, N-DBPs and total organic halogen (TOX) were reduced by 86.5, 75.4 and 81.1%, respectively. These removal efficiencies were significantly higher when compared with those obtained using a traditional activated carbon (AC) adsorption pretreatment process (42.7, 19.4 and 28.7%, respectively). By comprehensive toxicity calculations, a significant reduction in both the acute and chronic toxic potential of C-DBPs and N-DBPs were observed during the PATP COF adsorption process (with reduction rates of ~85 and ~ 75% observed for the C-DBPs and N-DBPs, respectively), which were comparable to the removal efficiencies observed for C-DBPs FP and N-DBPs FP by weight, suggesting the simultaneous and effective control of DBPs FP and their toxic potential. Cycling tests and stability trial also showed the excellent reusability, wide pH adaptability, and high stability of PATP COF, demonstrating its great potential application to the treatment of drinking water.

Assimilable organic carbon removal strategy for aquifer storage and recovery applications

Aquifer storage and recovery (ASR) technology has been adopted as a strategic water management tool. However, during the injection of oxic and organic carbon-containing water to the underground aquifers, severe phenomena such as clogging and groundwater deterioration have been reported. To prevent these severe phenomena, assimilable organic carbon (AOC) concentration has been controlled in the ASR applications by supporting bacteria growth potential. In this study, the AOC removal strategy was investigated in a simulated ASR system using an indigenous bacterium, Pseudomonas jinjuensis. AOC removal was evaluated under three different experimental conditions: (i) 30 °C and aerobic, (ii) 15 °C and aerobic, and (iii) 15 °C and anoxic. The effects of contact media such as sand and granular activated carbon on AOC removal efficiency were also investigated. Results show that under the 30 °C aerobic condition, P. jinjuensis could remove 99.8% (13 μg L^-1) of AOC with soil. The variations in the organic fractions determined by liquid chromatography with organic carbon detector analysis were observed and showed trends similar to those of AOC determined by the flow cytometry method. The indirect injection method in ASR application was recommended due to the AOC removal benefit by soil indigenous bacterium.

Assessing Additivity of Cytotoxicity Associated with Disinfection Byproducts in Potable Reuse and Conventional Drinking Waters

Recent studies used the sum of the measured concentrations of individual disinfection byproducts (DBPs) weighted by their Chinese hamster ovary (CHO) cell cytotoxicity LC₅₀ values to estimate the DBP-associated cytotoxicity of disinfected waters. This approach assumed that cytotoxicity was additive rather than synergistic or antagonistic. In this study, we evaluated whether this assumption was valid for mixtures containing DBPs at the concentration ratios measured in authentic disinfected waters. We examined the CHO cell cytotoxicity of defined DBP mixtures based on the concentrations of 43 regulated and unregulated DBPs measured in eight drinking and potable reuse waters. The hypothesis for additivity was supported using three experimental approaches. First, we demonstrated that the calculated additive toxicity (CAT) and bioassay-based calculated additive toxicity (BCAT) of the DBP mixtures agree within 12% on a median basis. We also found an additive toxicity response (CAT ≈ BCAT) between the regulated and unregulated DBP classes. Finally, the empirical biological cytotoxicity of the DBP subset mixtures, independent of the calculated toxicity, was additive. These results support the validity of using the sum of cytotoxic potency-weighted DBP concentrations as an estimate of the CHO cell cytotoxicity associated with known DBPs in real disinfected waters.

Precise exposure assessment revealed the cancer risk and disease burden caused by trihalomethanes and haloacetic acids in Shanghai indoor swimming pool water

Swimming pool disinfection byproducts (DBPs) are becoming increasingly common worldwide. Precise exposure and health risk assessment for DBPs in swimming pool water with optimized parameters for local and specific population is more urgently needed. This study aimed to determine the levels of trihalomethanes (THMs) and haloacetic acids (HAAs) in 16 public indoor swimming pools in Shanghai, China. Swimming habits were also investigated to obtain more accurate exposure assessment parameters. Precise exposure assessment through multiple pathways, resulting cancer risk, and disability-adjusted life years (DALYs) were assessed. Results indicated that the highest total level of THMs and HAAs occurred in autumn. The surveyed swimmers 9-17 years of age had higher average daily dose (ADD) of DBPs than swimmers ≥18 years of age. The total lifetime cancer risk (LCR) attributable to THMs and HAAs exceeded 10^-6, which represents a negligible risk level (NRL). The cancer risk from inhalation exposure predominantly by THMs contributed more than 99% of the total risk. Annual disease burden was 19.0 person-years attributed to exposure of DBPs in swimming pool water in Shanghai. This study provides a paradigm and strategic reference of precise exposure assessments, risk assessments, and disease burden estimation of hazards in swimming pool water for other regions.

GAC to BAC: Does it make chloraminated drinking water safer?

Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4-27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.

Nonhalogenated Aromatic DBPs in Drinking Water Chlorination: A Gap between NOM and Halogenated Aromatic DBPs

Halogenated disinfection byproducts (DBPs) are generated via reactions with natural organic matter (NOM) in chlorine disinfection of drinking water. How large NOM molecules are converted to halogenated aliphatic DBPs during chlorination remains a fascinating yet largely unresolved issue. Recently, many relatively toxic halogenated aromatic DBPs have been identified in chlorinated drinking waters, and they behave as intermediate DBPs to decompose to halogenated aliphatic DBPs. There is still one gap between NOM and halogenated aromatic DBPs. In this study, nine nonhalogenated aromatic compounds were identified as new intermediate DBPs in chlorination, including 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 3-formyl-4-hydroxybenzoic acid, salicylic acid, 5-formyl-2-hydroxybenzoic acid, 4-hydroxyphthalic acid, 4'-hydroxyacetophenone, 4-methylbenzoic acid, and 4-hydroxy-3-methylbenzaldehyde. These nonhalogenated aromatic DBPs formed quickly and reached the maximum levels at relatively low chlorine doses within a short contact time, and their formation pathways were proposed. The formation kinetics of three nonhalogenated aromatic DBPs and their corresponding monochloro-/dichloro-substitutes during chlorination were then modeled. The nonhalogenated aromatic DBPs contributed up to 84% of the formed monochloro-substitutes and 22% of the formed dichloro-substitutes, demonstrating that they somewhat acted as intermediates between NOM and halogenated aromatic DBPs. Furthermore, the formed nonhalogenated aromatic DBPs were found to be removed by >50% by granular activated carbon adsorption.

Factors Associated with Exposure to Trihalomethanes, NHANES 2001-2012

Disinfection is critical for maintaining a safe water supply, but the use of chlorine or chloramine leads to exposure to disinfection byproducts (DBPs), including trihalomethanes (THMs), which have been associated with adverse reproductive outcomes and bladder cancer. The U.S. Environmental Protection Agency revised the DBP regulations starting in 1998 to further limit levels of THMs in household water. We analyzed data from the National Health and Nutrition Examination Survey (NHANES) collected between 2001 and 2012 (with 2 years per cycle) using models with and without water-related predictors to examine the utility of including these measures. Median blood chloroform levels (25th-75th percentiles) were 16.2 (9.13-31.2) ng/L in 2001-2002 and 5.97 (2.92-12.3) ng/L in 2011-2012. Median blood bromodichloromethane (BDCM) levels (25th-75th percentiles) were 2.22 (1.06-4.61) ng/L in 2001-2002 and 1.18 (<limit of detection-2.92) ng/L in 2011-2012. THM water concentrations and measures of the recency since time spent in water use activities were associated with blood THM levels. Being in a pool/hot tub/sauna within 24 h or taking a shower/bath within 6 h of blood collection was associated with elevated blood levels of chloroform and BDCM. When possible, it is important to include recency and external dose when assessing associations to internal dose levels for nonpersistent compounds.

Global Transcriptional Analysis of Nontransformed Human Intestinal Epithelial Cells (FHs 74 Int) after Exposure to Selected Drinking Water Disinfection By-Products

BACKGROUND

Drinking water disinfection inadvertently leads to the formation of numerous disinfection by-products (DBPs), some of which are cytotoxic, mutagenic, genotoxic, teratogenic, and potential carcinogens both in vitro and in vivo.

OBJECTIVES

We investigated alterations to global gene expression (GE) in nontransformed human small intestine epithelial cells (FHs 74 Int) after exposure to six brominated and two chlorinated DBPs: bromoacetic acid (BAA), bromoacetonitrile (BAN), 2,6-dibromo-p-benzoquinone (DBBQ), bromoacetamide (BAM), tribromoacetaldehyde (TBAL), bromate (BrO3-), trichloroacetic acid (TCAA), and trichloroacetaldehyde (TCAL).

METHODS

Using whole-genome cDNA microarray technology (Illumina), we examined GE in nontransformed human cells after 4h exposure to DBPs at predetermined equipotent concentrations, identified significant changes in gene expression (p≤0.01), and investigated the relevance of these genes to specific toxicity pathways via gene and pathway enrichment analysis.

RESULTS

Genes related to activation of oxidative stress-responsive pathways exhibited fewer alterations than expected based on prior work, whereas all DBPs induced notable effects on transcription of genes related to immunity and inflammation.

DISCUSSION

Our results suggest that alterations to genes associated with immune and inflammatory pathways play an important role in the potential adverse health effects of exposure to DBPs. The interrelationship between these pathways and the production of reactive oxygen species (ROS) may explain the common occurrence of oxidative stress in other studies exploring DBP toxicity. Finally, transcriptional changes and shared induction of toxicity pathways observed for all DBPs caution of additive effects of mixtures and suggest further assessment of adverse health effects of mixtures is warranted. https://doi.org/10.1289/EHP4945.

Assessment of the in vitro toxicity of the disinfection byproduct 2,6-dichloro-1,4-benzoquinone and its transformed derivatives

An emerging class of unregulated disinfection byproducts, halobenzoquinones (HBQs), has gained recent interest following suggestions of enhanced toxicity compared to regulated disinfection byproducts. While the kinetics of HBQ hydrolysis in water have been well characterized, the stability of HBQs in cell culture media, a critical parameter when evaluating toxicity in vitro, has been overlooked. The objective of this study was: (1) to contrast the stability of a prevalent HBQ, 2,6-dichloro-1,4-benzoquinone (DCBQ), in cell culture media and water, and (2) to evaluate the cytotoxicity of parent and transformed DCBQ compounds as well as the ability of these compounds to generate intracellular reactive oxygen species (ROS) in normal human colon cells (CCD 841 CoN) and human liver cancer cells (HepG2). The half-life of DCBQ in cell media was found to be less than 40 min, compared to 7.2 h in water at pH 7. DCBQ induced a concentration-dependent decrease in cell viability and increase in ROS production in both cell lines. The parent DCBQ compound was found to induce significantly greater cytotoxicity compared to transformed DCBQ products. We demonstrate that the study design used by most published studies (i.e., extended exposure periods) has led to a potential underestimation of the cytotoxicity of HBQs by evaluating the toxicological profile primarily of transformed HBQs, rather than corresponding parent compounds. Future in vitro toxicological studies should account for HBQ stability in media to evaluate the acute cytotoxicity of parent HBQs.