Drinking water disinfection byproduct iodoacetic acid affects thyroid hormone synthesis in Nthy-ori 3-1 cells.

Iodoacetic acid (IAA) is an emerging and the most genotoxic iodinated disinfection byproduct to date. IAA can disrupt the thyroid endocrine function in vivo and in vitro, but the underlying mechanisms remain unclear. In this work, transcriptome sequencing was used to investigate the effect of IAA on the cellular pathways of human thyroid follicular epithelial cell line Nthy-ori 3-1 and determine the mechanism of IAA on the synthesis and secretion of thyroid hormone (TH) in Nthy-ori 3-1 cells. Results of transcriptome sequencing indicated that IAA affected the TH synthesis pathway in Nthy-ori 3-1 cells. IAA reduced the mRNA expression of thyroid stimulating hormone receptor, sodium iodide symporter, thyroid peroxidase, thyroglobulin, paired box 8 and thyroid transcription factor-2, inhibited the cAMP/PKA pathway and Na+-K+-ATPase, and decreased the iodine intake. The results were confirmed by our previous findings in vivo. Additionally, IAA downregulated glutathione and the mRNA expression of glutathione peroxidase 1, leading to increased reactive oxygen species production. This study is the first to elucidate the mechanisms of IAA on TH synthesis in vitro. The mechanisms are associated with down-regulating the expression of genes related to TH synthesis, inhibiting iodine uptake, and inducing oxidative stress. These findings may improve future health risk assessment of IAA on thyroid in human.

Disinfection byproducts in indoor swimming pool water: Detection and human lifetime health risk assessment.

Quantification of regulated and emerging disinfection byproducts (DBPs) in swimming pool water, as well as the assessment of their lifetime health risk are limited in China. In this study, the occurrence of regulated DBPs (e.g., trihalomethanes, haloacetic acids) and emerging DBPs (e.g., haloacetonitriles, haloacetaldehydes) in indoor swimming pool water and the corresponding source water at a city in Eastern China were determined. The concentrations of DBPs in swimming pool water were 1-2 orders of magnitude higher than that in source water. Lifetime cancer and non-cancer risks of DBPs stemming from swimming pool water were also estimated. Inhalation and dermal exposure were the most significant exposure routes related to swimming pool DBP cancer and non-cancer risks. For the first time, buccal and aural exposure were considered, and were proven to be important routes of DBP exposure (accounting for 17.9%-38.9% of total risk). The cancer risks of DBPs for all swimmers were higher than 10-6 of lifetime exposure risk recommended by United States Environmental Protection Agency, and the competitive adult swimmers experienced the highest cancer risk (7.82 × 10-5). These findings provide important information and perspectives for future efforts to lower the health risks associated with exposure to DBPs in swimming pool water.

Assessing microbial and chemical exposure risks of Giardia in indoor swimming pool water disinfected by chlorine.

Swimming pools adopt chlorination to ensure microbial safety. Giardia has attracted attention in swimming pool water because of its occurrence, pathogenicity, and chlorine resistance. To control Giardia concentrations in pool water and reduce the microbial risk, higher chlorine doses are required during disinfection. Unfortunately, this process produces carcinogenic disinfection byproducts that increase the risk of chemical exposure. Therefore, quantitatively evaluating the comparative microbial vs. chemical exposure risks that stem from chlorination inactivation of Giardia in swimming pool water is an issue that demands attention. We simulated an indoor swimming pool disinfection scenario that followed common real-world disinfection practices. A quantitative microbial risk assessment coupled with a chemical exposure risk assessment was employed to compare the Giardia microbial exposure risk (MER) and the trihalomethane chemical exposure risk (CER) to humans. The results demonstrated a 22% decrease in MER- and CER-induced health exposure risk, from 8.45E-5 at 8:00 to 6.60E-5 at 19:00. Both the MER and CER decreased gradually, dropping to 3.26E-5 and 3.35E-5 at 19:00, respectively. However, the CER exceeded the MER after 18:30 and became the dominant factor affecting the total exposure risk. Past the 18 hr mark, the contribution of trihalomethane CER far exceeded the risk aversion from microbial inactivation, leading to a net increase in total exposure risk despite the declining MER. Swimmers may consider swimming after 19:00, when the total exposure risk is the lowest. Lowering water temperature and/or pH were identified as the most sensitive factors to minimize the overall health exposure risk.

Ozonation Treatment Increases Chlorophenylacetonitrile Formation in Downstream Chlorination or Chloramination.

Chlorophenylacetonitriles (CPANs) are an emerging group of aromatic nitrogenous disinfection byproducts (DBPs). However, their dominant precursors and formation pathways remain unclear, which hinders the further development of effective control strategies. For the first time, CPAN precursors were screened by conducting formation potential (FP) tests on real water samples from six drinking water treatment plants (DWTPs). The average overall removal of CPAN precursors across all six DWTPs was only 10%. Moreover, ozonation increased CPAN precursors by 140% on average. Fluorescence spectroscopy showed a dramatic reduction in aromatic proteins, tyrosine-like proteins, and tryptophan-like proteins following ozonation. Low-apparent-molecular-weight (AMW) (<1 kDa) substances were correlated with the CPAN FP in these samples. We therefore hypothesized that protein fragments with low AMW, such as amino acids, are important CPAN precursors during downstream chlor(am)ination. Two aromatic free amino acids, tyrosine and tryptophan, were selected to investigate the formation of CPANs during chlor(am)ination. Both amino acids were found to act as CPAN precursors for the first time. CPAN formation pathways from these model precursors were proposed based on the frontier molecular orbital theory and intermediate products identified using high-resolution mass spectrometry. This study provides a powerful theoretical foundation for controlling CPAN formation in drinking water.

Comparison of Estrogenic, Spectroscopic, and Toxicological Analyses of Pilot-Scale Water, Wastewaters, and Processed Wastewaters at Select Military Installations.

Reuse of water requires the removal of contaminants to ensure human health. We report the relative estrogenic activity (REA) of reuse treatment design scenarios for water, wastewaters, and processed wastewaters before and after pilot-scale treatment systems tested at select military facilities. The comparative relationships between REA, several composite toxicological endpoints, and spectroscopic indicators were evaluated for different reuse treatment trains. Four treatment processes including conventional and advanced treatments reduced the estrogenicity by at least 33%. Biologically based methods reduced estrogenicity to below detection levels. Conventional treatment scenarios led to significantly less reduction of adverse biological endpoints compared to the advanced treatment scenarios. Incorporating the anaerobic membrane bioreactor reduced more endpoints with higher reduction percentages compared to the sequencing batch reactor design. Membrane technology and advanced oxidation generated reductions across all biological endpoints, from 65% (genotoxicity) to 100% (estrogenicity). The design scenarios featuring a low-cutoff mechanical screen filter, intermittent activated carbon biofilter, and membrane filtration achieved the highest percent reduction and produced water with the lowest negative biological endpoints. Spectroscopic indicators demonstrated case-specific relationships with estrogenicity and toxicity. Estrogenicity consistently correlated with cytotoxicity and thiol reactivity, indicating the potential for preliminary estrogenicity screening using thiol reactivity.

Influence of Anaerobic Mesophilic and Thermophilic Digestion on Cytotoxicity of Swine Wastewaters.

Recycling wastewater from animal production for fertilizers using anaerobic digestion (AD) is a common method to recover the nutrients in the digestate. However, the digestate toxicity is not well understood because AD is mainly designed for chemical oxygen demand reduction. This study determined the toxicity during AD and the controlling factors with the goal to improve digestate safety during farmer handling to reuse the nutrients. Thermophilic and mesophilic AD of two swine wastewater sources were studied. Mammalian cell cytotoxicity revealed that the effluent after thermophilic digestion was at least 69% more toxic than the mesophilic effluent, owing to higher ammonia and total organic carbon in the former. Ammonia accounted for >55% total cytotoxicity, and the organics of the thermophilic digestate were twice more toxic than those in the mesophilic digestate. Despite less toxicity contribution than the ammonia, the organics did demonstrate significant adverse effects on the thiol-mediated cellular protection mechanism. For swine wastewater nutrient recovery, converting ammonia to less toxic nitrogen forms could lower the toxic hazard of the AD digestate. With much less ammonia, the organics would be the remaining decisive factor for toxicity, which is favorably reduced using thermophilic AD over mesophilic. If the ammonia is not reduced, mesophilic AD would generate a less toxic digestate.

Toxicological Comparison of Water, Wastewaters, and Processed Wastewaters.

Drinking water utilities will increasingly rely on alternative water sources in the future, including wastewater reuse. Safety must be assured in the application of advanced oxidation processes (AOPs) and supporting treatments for wastewater effluent reuse. This study developed toxicological profiles for source and tap waters, wastewaters, and treated effluents by different processes from four military installation locations. The objective of this study was to evaluate the toxicity of extracted organics from diverse source waters and after reuse treatments. The toxicity analyses included thiol reactivity, mammalian cell cytotoxicity, and genotoxicity. Differences in toxicity between source or tap waters and effluents from wastewater treatment processes supported AOP treatment to reduce risks of potable reuse. An anoxic and aerobic activated sludge process followed by sand filtration controlled toxicity to levels similar to a municipal drinking water. An anaerobic membrane bioreactor process exceeded the toxicity levels of a typical drinking water. Two AOP processes (ultraviolet (UV) + reverse osmosis (RO) + chlorination (NaOCl) or RO + UV-H2O2 + NaOCl) significantly reduced toxicity. The integration of the wastewater systems with ultrafiltration, AOP, and RO was effective to reduce the toxicity to levels comparable to, or better than, tap water samples.

Thiol Reactivity Analyses To Predict Mammalian Cell Cytotoxicity of Water Samples.

An in chemico high throughput assay based on N-acetylcysteine was developed and used in conjunction with previous and new mammalian cell cytotoxicity data. Our objective was to derive an empirical equation with confidence levels for mammalian cell cytotoxicity prediction. Modeling data included 16 unique sources of waters and wastewaters of distinct water qualities to encompass a wide range of real environmental samples. This approach provides a quick screen to identify those water and wastewaters that could be prioritized for in depth analytical biological analyses and toxicity. The resulting model can serve as a preliminary convenient tool to screen for potential mammalian cell cytotoxicity in organic extracts of a wide variety of water samples.

Spectroscopic Indicators for Cytotoxicity of Chlorinated and Ozonated Effluents from Wastewater Stabilization Ponds and Activated Sludge.

We investigated chronic mammalian cell cytotoxicity of wastewaters from four sources and their optical spectroscopic properties with or without chlorination or ozonation. Samples from effluents of activated sludge, nitrification tower, facultative waste stabilization pond, and maturation waste stabilization pond were either chlorinated or ozonated. The wastewater samples were analyzed for fluorescence excitation emission matrix, specific fluorescence index (SFI), and specific UV absorbance at 254 nm (SUVA). Before and after disinfection the wastewater samples were quantitatively analyzed for in vitro mammalian cell cytotoxicity. We found that the organic extracts from the ozonated samples induced lower cytotoxicity responses than those from the chlorinated or the nondisinfected samples. To develop correlations between SFI, SUVA, and cytotoxicity, we analyzed 21 independent samples. Significant linear correlations found among these samples suggest that under the tested conditions, cytotoxicity was preferentially influenced by the fluorescence and SUVA of their composite organic agents. These two spectroscopic parameters may be used as indicators for the potential cytotoxicity of nondisinfected, ozonated, or chlorinated municipal wastewaters.

Toxicity of Wastewater with Elevated Bromide and Iodide after Chlorination, Chloramination, or Ozonation Disinfection.

Water reuse is receiving unprecedented attention as many areas around the globe attempt to better-manage their fresh water resources. Wastewaters in coastal regions may contain elevated levels of bromide (Br-) and iodide (I-) from seawater intrusion or high mineral content in the source waters. Disinfection of such wastewater is essential to prevent the spread of pathogens; however, little is known about the toxicity of the treated wastewater. In this study, we evaluated the genotoxicity to Chinese hamster ovary (CHO) cells induced by municipal secondary wastewater effluent amended with elevated Br- and I- after disinfection by chlorine, chloramines, or ozone. We calibrated and applied an N-acetylcysteine (NAC) thiol reactivity assay as a surrogate for thiol reactivity with biological proteins (glutathione) of wastewater samples. Chlorination of wastewaters produced CHO cell genotoxicity comparable to chloramination, 3.9 times more genotoxic than the nondisinfected controls. Ozonated wastewater was at least 3 times less genotoxic than the samples treated with chlorine-based disinfectants and was not significantly different compared with the nondisinfected controls. Positive and significant correlations were observed among genotoxicity, cytotoxicity, and NAC thiol reactivity for all disinfected samples. These results indicate that the ozonation of wastewater with high Br- and I- levels may yield organics with lower genotoxicity to CHO cells than chlorine-based disinfection. NAC thiol reactivity, although excluding the possible effect of bromate from ozonation in this work, could be used as a rapid in chemico screen for potential genotoxicity and cytotoxicity in mammalian cells exposed to disinfected wastewaters.

Comparative mammalian cell cytotoxicity of wastewater with elevated bromide and iodide after chlorination, chloramination, or ozonation.

Recycling wastewater is becoming more common as communities around the world try to better control their water resources against an increased frequency of either prolonged droughts or intense flooding. For communities in coastal areas, wastewaters may contain elevated levels of bromide (Br-) and iodide (I-) from seawater intrusion or high mineral content of source waters. Disinfection of such wastewater is mandatory to prevent the spread of pathogens, however little is known about the toxicity of wastewater after disinfection in the presence of Br- and I-. In this study we compared the induction of chronic cytotoxicity in mammalian cells in samples of municipal secondary wastewater effluent amended with elevated levels of Br-/I- after disinfection by chlorine, chloramines or ozone to identify which disinfection process generated wastewater with the lowest level of adverse biological response. Chlorination increased mammalian cell cytotoxicity by 5 times as compared to non-disinfected controls. Chloramination produced disinfected wastewater that expressed 6.3 times more cytotoxicity than the non-disinfected controls and was 1.3 times more cytotoxic than the chlorinated samples. Ozonation produced wastewater with cytotoxicity comparable to the non-disinfected controls and was at least 4 times less cytotoxic than the chlorine disinfected wastewaters. These results indicate that compared to chlorination and chloramination, ozonation of wastewater with high Br-/I- levels yielded the lowest mammalian cell cytotoxicity, suggesting its potential as a more favorable method to disinfect wastewater with minimizing the biological toxicity in mind.

Comparative Mammalian Cell Cytotoxicity of Wastewaters for Agricultural Reuse after Ozonation.

Reusing wastewater in agriculture is becoming increasingly common, which necessitates disinfection to ensure reuse safety. However, disinfectants can react with wastewater constituents to form disinfection byproducts (DBPs), many of which are toxic and restrict the goal of safe reuse. Our objective was to benchmark the induction of mammalian cell cytotoxicity after ozonation against chlorination for three types of real wastewaters: municipal secondary effluent and two sources of minimally treated swine farm wastewaters. A new method to evaluate samples of suspected high cytotoxicity was devised. For the secondary effluent, ozonation reduced the cytotoxicity by as much as 10 times; chlorination lowered the cytotoxicity only when followed by dechlorination. The swine farm wastewaters were up to 2000 times more cytotoxic than the secondary effluent, and the highest reduction in cytotoxicity was 17 times as achieved by ozonation. These results indicate that secondary effluent is preferred over swine wastewaters for agricultural reuse regardless of the tested disinfectants. Ozonation consistently reduced the cytotoxicity of both the full strength and the organic extracts of all tested wastewaters more than chlorination. The only significant correlation was observed in the secondary wastewater between total haloacetonitriles and cytotoxicity. While the association of reduced toxicity with the modification or reduction of specific compound(s) is unclear, regulated DBPs may not be the primary forcing agents.

Persistence of Bacteroides ovatus under simulated sunlight irradiation.

BACKGROUND: Bacteroides ovatus, a member of the genus Bacteroides, is considered for use in molecular-based methods as a general fecal indicator. However, knowledge on its fate and persistence after a fecal contamination event remains limited. In this study, the persistence of B. ovatus was evaluated under simulated sunlight exposure and in conditions similar to freshwater and seawater. By combining propidium monoazide (PMA) treatment and quantitative polymerase chain reaction (qPCR) detection, the decay rates of B. ovatus were determined in the presence and absence of exogenous photosensitizers and in salinity up to 39.5 parts per thousand at 27°C. RESULTS: UVB was found to be important for B. ovatus decay, averaging a 4 log10 of decay over 6 h of exposure without the presence of extracellular photosensitizers. The addition of NaNO2, an exogenous sensitizer producing hydroxyl radicals, did not significantly change the decay rate of B. ovatus in both low and high salinity water, while the exogenous sensitizer algae organic matter (AOM) slowed down the decay of B. ovatus in low salinity water. At seawater salinity, the decay rate of B. ovatus was slower than that in low salinity water, except when both NaNO2 and AOM were present. CONCLUSION: The results of laboratory experiments suggest that if B. ovatus is released into either freshwater or seawater environment in the evening, 50% of it may be intact by the next morning; if it is released at noon, only 50% may be intact after a mere 5 min of full spectrum irradiation on a clear day. This study provides a mechanistic understanding to some of the important environmental relevant factors that influenced the inactivation kinetics of B. ovatus in the presence of sunlight irradiation, and would facilitate the use of B. ovatus to indicate the occurrence of fecal contamination.

Insights into the transformation of natural organic matter during UV/peroxydisulfate treatment by FT-ICR MS and machine learning: Non-negligible formation of organosulfates.

Natural organic matter (NOM) is a major sink of radicals in advanced oxidation processes (AOPs) and understanding the transformation of NOM is important in water treatment. By using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in conjunction with machine learning, we comprehensively investigated the reactivity and transformation of NOM, and the formation of organosulfates during the UV/peroxydisulfate (PDS) process. After 60 min UV/PDS treatment, the CHO formula number and dissolved organic carbon concentration significantly decreased by 83.4 % and 74.8 %, respectively. Concurrently, the CHOS formula number increased substantially from 0.7 % to 20.5 %. Machine learning identifies DBE and AImod as the critical characteristics determining the reactivity of NOM during UV/PDS treatment. Furthermore, linkage analysis suggests that decarboxylation and dealkylation reactions are dominant transformation pathways, while the additions of SO3 and SO4 are also non-negligible. According to SHAP analysis, the m/z, number of oxygens, DBE and O/C of NOM were positively correlated with the formation of organosulfates in UV/PDS process. 92 organosulfates were screened out by precursor ion scan of HPLC-MS/MS and verified by UPLC-Q-TOF-MS, among which, 7 organosufates were quantified by authentic standards with the highest concentrations ranging from 2.1 to 203.0 ng L‒1. In addition, the cytotoxicity of NOM to Chinese Hamster Ovary (CHO) cells increased by 13.8 % after 30 min UV/PDS treatment, likely responsible for the formation of organosulfates. This is the first study to employ FT-ICR MS combined with machine learning to identify the dominant NOM properties affecting its reactivity and confirmed the formation of organosulfates from sulfate radical oxidation of NOM.

Biomimetic cytotoxicity control of select nitrogenous disinfection byproducts in water.

Nitrogenous disinfection byproducts (N-DBPs) in water are carcinogenic, teratogenic, and mutagenic. In this work, we developed a biomimetic reduction approach based on the cysteine thiol that destructed the highly toxic, select nitrogenous haloacetamides (HAMs) and haloacetonitriles (HANs) while effectively controlling the cytotoxicity of the degradation products to serve as a basis for further technological applications (e.g. immobilized contact bed for terminal users). Mechanisms on toxicity control were elucidated. Results showed the degradation and cytotoxicity control of HAMs as more efficient than that of the HANs. The cytotoxicity of the chlorinated, brominated, and iodinated HAMs and HANs was reduced to 25 %- 0.25 % of the original after biomimetic reduction using a reasonable concentration ratio. Through a combination of thiol-specific reactivity, dehalogenation, and quantitative structure-activity relationship analyses, the major toxicity control mechanisms were found to be the reductive dehalogenation of the N-DBPs. The halogenated functional groups on the N-DBPs had a more pronounced effect than the amide and nitrile groups on the cytotoxicity and detoxification effect. Patterns of toxicity interaction variations with DBPs concentrations were identified to detect possible synergistic cytotoxicity interactions under various combinations of HAMs and HANs in the presence of the cysteine thiol. Results could benefit future N-DBPs control efforts.

Persistence kinetics of a novel disinfectant peracetic acid for swimming pool disinfection.

Disinfection is essential to swimming pool water (SPW) quality. Peracetic acid (PAA) has attracted attention for water disinfection for advantages such as less formation of regulated DBPs. Persistence kinetics of disinfectants is difficult to elucidate in pools because of the complex water matrix stemming from body fluid loadings from swimmers and long residence times. In this research, the persistence kinetics of PAA was investigated in SPW benchmarked against free chlorine, use bench-scale experiments and model simulation. Kinetics models were developed to simulate the persistence of PAA and chlorine. The stability of PAA was less sensitive to swimmer loadings than chlorine. An average swimmer loading event reduced the apparent decay rate constant of PAA by 66 %, a phenomenon that diminished with increasing temperatures. L-histidine and citric acid from swimmers were identified as main retardation contributors. By contrast, a swimmer loading event instantaneously consumed 70-75 % of the residual free chlorine. The required total dose of PAA was 97 % less than chlorine under the 3-days cumulative disinfection mode. Temperature was positively correlated with disinfectant decay rate, with PAA being more sensitive than chlorine. These results shed light on the persistence kinetics of PAA and its influential factors in swimming pool settings.

Evidence-based identification of breast cancer and associated ovarian and uterus cancer risk components in source waters from high incidence area in the Pearl River Basin, China.

Breast cancer, ovarian cancer, and uterus cancer are among the most common female cancers. They are suspected to associate with exposures to specific environmental pollutants, which remain unidentified in source waters. In this work, we focused on the Pearl River Basin region in China, which experienced a high incidence of breast, ovarian, and uterus cancers. Combining cancer patient data, mammalian cell cytotoxicity analyses, and exhaustive historical and current chemical assessments, we for the first time identified source water components that promoted proliferation of mammalian cells, and confirmed their association with these female cancers via the estrogen receptor mediated pathway. Therefore, the components that have previously been found to enhance the proliferation of estrogen receptor-containing cells through endocrine disruption could be the crucial factor. Based on this, components that matched with this toxicological characteristic (i.e., estrogen-like effect) were further identified in source waters, including (1) organic components: phthalates, bisphenol A, nonylphenols, and per-/polyfluoroalkyls; (2) inorganic components: Sb, Co, As, and nitrate. Moreover, these identified water components were present at levels comparable to other regions with high female cancer prevalence, suggesting that the potential risk of these components may not be exclusive to the study region. Together, multiple levels of evidence suggested that long-term co-exposures to source water estrogenic components may be important to the development of breast, ovarian, and uterus cancers.

Hydrophile-lipophile balance solid phase extraction of surface water organics: Fluorescent elution preference and overlooked fractions.

Fluorescent dissolved organic matter (FDOM) in surface water has broad implications on water quality research and operations. Solid phase extraction (SPE) is the most widely used technique to extract FDOM. However, fluorescent elution preferences by common solvents and content of quantifiable chromophores in waste fraction remain largely unknown, both quantitatively and qualitatively. In this work, the preferential selection of various types of FDOM captured by and lost from SPE as characterized by the fluorescence excitation-emission matrix (EEM) were investigated. Three elution solvents (methanol, acetone, and dichloromethane) were adopted to elute the DOM that was enriched on a typical SPE sorbent. Results revealed that high polarity (methanol) and medium polarity (acetone) solvents eluted the highest variety and quantity of humic acid-like substances (Region V), while the low polarity (dichloromethane) elution solvent was more suitable for eluting tyrosine (Region I) and tryptophan (Region II). Compared to eluting only with methanol, sequential elution and recombination using the three aforementioned solvents demonstrated a significant increase in not only DOC recovery (by 7%), but fluorescence integral values and fluorescence characteristics covering collectively much larger fluorescence regions that more closely resembled raw water. For the first time, the fluorescence EEM of waste after loading the sample revealed a previously overlooked FDOM loss of 20%, caused by ineffective adsorption onto the solid phase resin. Substantial carbonaceous and nitrogenous FDOM were present in this fraction (the fluorescence intensity of aromatic protein in waste exceeds 20% of that in raw water), indicating possible underestimations of FDOM-related research in areas such as disinfection byproduct and toxicity work. The results of this study provide both a qualitative and quantitative characterization of the elution and lost products of SPE in capturing FDOM.

Simultaneous modulation of CHO cell cytotoxicity, turbidity, and DOC by coagulation with or without pre-oxidation in water from the Pearl River Delta region, China.

Coagulation with or without pre-oxidation are important drinking water treatment processes. However, the efficacy of these processes in mitigating water toxicity remains unknown. To further improve drinking water safety, we employed water from the Pearl River Delta region of southern China to investigate a treatment approach consisting of coagulation with or without pre-oxidation to simultaneously modulate health-relevant cytotoxicity to CHO cells, on top of the conventional foci of turbidity and dissolved organic carbon (DOC) during water treatment. Three coagulants (two aluminum-based and one iron-based salts) and three pre-oxidants (ozone, permanganate, and peroxymonosulfate) were studied. For coagulation without pre-oxidation, intermediate coagulant doses and pH reached optimum cytotoxicity to CHO cells, turbidity, and DOC control simultaneously. Introducing oxidants reduced cytotoxicity to CHO cells significantly, enhanced by increasing oxidant concentrations and pre-oxidation duration. The cytotoxicity to CHO cells mitigation capabilities of three pre-oxidants were: ozone > peroxymonosulfate > potassium permanganate. Modulation of water cytotoxicity to CHO cells was mostly attributable to controlling DOC (specifically humic-acid like substances, tyrosine, tryptophan). However, the addition of pre-oxidants led to significant shifts in water cytotoxicity to CHO cells forcing drivers, rendering humic-acid like substances the sole decisive cytotoxicity-inducing fluorophores. For the first time, 'sweet spots' were identified to simultaneously monitor cytotoxicity to CHO cells alongside turbidity and DOC. These methods better modulate water cytotoxicity to CHO cells without sacrificing conventional water treatment goals while shedding light onto the mechanisms behind.

Dramatically increased disinfection byproducts in swimming pool water caused by commonly used urea degradants.

In China, urea degradants are often used in combination with chlorine in swimming pool water to remove urea. Here we report the first study about the impacts of urea degradants on urea degradation, disinfection byproduct (DBP) formation and estimated DBP-associated cytotoxicity and genotoxicity. Firstly, four groups of typical DBPs from six real indoor swimming pools were analyzed. The concentration of DBPs in swimming pool waters was about 1-2 orders of magnitude higher than that source tap water. Notably, a rapid increase in DBPs was observed after urea degradant treatment. Simulated processes of urea removal using three commonly used urea degradants were therefore conducted in laboratory. Neither urea degradant nor chlorine alone removed urea effectively within 48 h. When applied in combination, urea degradant with sufficient chlorine rapidly removed urea by 100% within 3 h, and anti-chlorourea oligomer in urea degradants was the main contributor. Meanwhile, a remarkable increase in DBPs, especially brominated DBPs, was observed due to bromide introduction by urea degradants. For this reason, bromine incorporation factor (BIF) of DBPs dramatically increased. For instance, the BIF of dihaloacetic acids increased by 2665%-4025% after applying three urea degradants. As the highly toxic brominated DBPs were generated, attention should be paid into the potential DBP-related health risks from the use of urea degradants together with chlorine.