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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Catalytic hydrolysis: A novel role of zero-valent iron in haloacetonitrile degradation and transformation in unbuffered systems.

Efforts to remove highly toxic haloacetonitriles (HANs) is an important step to reduce health risks associated with disinfection by product exposure. Zero valent iron (ZVI) is a versatile material, whose reductant, sorbent and coagulant role has been well understood. However, their catalytic role is less known. In this study, the degradation and transformation of HANs in ZVI system were investigated. Significant decreases of the four HANs in ZVI system were observed, and haloacetamides and haloacetic acids (hydrolysis products of HANs) were the dominant transformation products of HANs. However dehalogenated HANs, Fe (II) and Fe (III) were rarely detected after reaction, indicating that the ZVI acted as a catalyst to promote the hydrolysis of HANs, rather than other previously reported causes (dehalogenation or redox reaction). The HAN degradation rates were dramatically affected by the initial pH, ZVI doses and initial HAN concentration. Kinetic analysis indicated that HAN removal was enhanced with the increase of initial pH (5-9), ZVI doses (1-10 g/L), and initial HAN concentration (25-200 µg/L). ZVI induced the transformation of HANs to haloacetamides, haloacetic acids and other de-halogenated compounds, which reduced the cytotoxicity and genotoxicity by 88% and 85%, respectively. This study helped to understand the fate of HAN during the transmission in cast iron pipes, and provided a theoretical foundation for future HAN control and monitoring efforts.

Transformation of antiviral ribavirin during ozone/PMS intensified disinfection amid COVID-19 pandemic.

Due to the spread of coronavirus disease 2019 (COVID-19), large amounts of antivirals were consumed and released into wastewater, posing risks to the ecosystem and human health. Ozonation is commonly utilized as pre-oxidation process to enhance the disinfection of hospital wastewater during COVID-19 spread. In this study, the transformation of ribavirin, antiviral for COVID-19, during ozone/PMS­chlorine intensified disinfection process was investigated. •OH followed by O3 accounted for the dominant ribavirin degradation in most conditions due to higher reaction rate constant between ribavirin and •OH vs. SO4•- (1.9 × 109 vs. 7.9 × 107 M-1 s-1, respectively). During the O3/PMS process, ribavirin was dehydrogenated at the hydroxyl groups first, then lost the amide or the methanol group. Chloride at low concentrations (e.g., 0.5- 2 mg/L) slightly accelerated ribavirin degradation, while bromide, iodide, bicarbonate, and dissolved organic matter all reduced the degradation efficiency. In the presence of bromide, O3/PMS process resulted in the formation of organic brominated oxidation by-products (OBPs), the concentration of which increased with increasing bromide dosage. However, the formation of halogenated OBPs was negligible when chloride or iodide existed. Compared to the O3/H2O2 process, the concentration of brominated OBPs was significantly higher after ozonation or the O3/PMS process. This study suggests that the potential risks of the organic brominated OBPs should be taken into consideration when ozonation and ozone-based processes are used to enhance disinfection in the presence of bromide amid COVID-19 pandemic.

The occurrence and control of waterborne viruses in drinking water treatment: A review.

As the coronavirus disease 2019 continues to spread globally, its culprit, the severe acute respiratory syndrome coronavirus 2 has been brought under scrutiny. In addition to inhalation transmission, the possible fecal-oral viral transmission via water/wastewater has also been brought under the spotlight, necessitating a timely global review on the current knowledge about waterborne viruses in drinking water treatment system - the very barrier that intercepts waterborne pathogens to terminal water users. In this article we reviewed the occurrence, concentration methods, and control strategies, also, treatment performance on waterborne viruses during drinking water treatment were summarized. Additionally, we emphasized the potential of applying the quantitative microbial risk assessment to guide drinking water treatment to mitigate the viral exposure risks, especially when the unregulated novel viral pathogens are of concern. This review paves road for better control of viruses at drinking water treatment plants to protect public health.

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.

Effect of disinfectant residuals on infection risks from Legionella pneumophila released by biofilms grown under simulated premise plumbing conditions.

The ubiquitous presence of biofilms in premise plumbing and stagnation, which commonly occurs in premise plumbing, can exacerbate the decay of chlorine residual in drinking water. Using biofilms grown in a simulated premise plumbing setup fed directly with freshly treated water at two full-scale water treatment plants, we previously determined the mass transfer coefficients for chlorine decay in premise plumbing. These coefficients coupled with inactivation kinetics of L. pneumophila released from biofilms reported previously were integrated into a Monte Carlo framework to estimate the infection risk of biofilm-derived L. pneumophila from 1 to 48 h of stagnation. The annual infection risk was significantly higher when water stayed stagnant for up to 48 h in pipes covered internally with biofilms, compared to clean pipes without biofilms. The decay of residual chlorine due to biofilms during 48-hour stagnation led to up to 6 times increase in the annual infection risk compared to the case where biofilms was absent. Global sensitivity analysis revealed that the rate of L. pneumophila detachment from biofilms and the decay of chlorine residual during stagnation are the two most important factors influencing the infection risks. Stagnation caused by water use patterns and water-saving devices in the premise plumbing can lead to increased infection risk by biofilm-derived L. pneumophila. Overall, this study's findings suggested that biofilms could induce chlorine decay and consequently increase L. pneumophila infection risk. Thus, reducing stagnation, maintaining residual chlorine, and suppressing biofilm growth could contribute to better management of L. pneumophila infection risk.

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.

The impact of disinfection Ct values on cytotoxicity of agricultural wastewaters: Ozonation vs. chlorination.

Toxicity arising from toxic disinfection byproducts is an unintended result of disinfection during water reclamation. To ensure safe water reclamation treatment, it is important to develop a disinfection strategy with minimal formation of overall toxicity in the reclaimed water. The cumulative disinfectant concentration over time (Ct) is a useful concept for pathogen control during reuse water disinfection. We evaluated the toxicity impact of Ct values and different methods to achieve identical Ct values by ozonation or chlorination of wastewaters from four agricultural sources on mammalian cells. N-acetylcysteine (NAC) reactivity of the wastewater organic extracts was determined to reveal their impact on the thiol-specific biological detoxification mechanism. The results demonstrated that for two sources and for both ozonation and chlorination, higher Ct values enhanced cytotoxicity. The ozonated waters were at least 10% less toxic and as much as 22.4 times less toxic than either the non-disinfected controls or the chlorinated waters. Chlorination consistently induced higher cytotoxicity than ozonation by between 2.2 and 22.4 fold, respectively, and induced similar or higher cytotoxicity than the non-disinfected controls, by at most 4.4 fold. Given the same Ct values, the combination of high disinfectant concentration and short contact time produced finished wastewaters with higher toxicity, than the combination of low disinfectant concentration and long contact time. NAC thiol reactivity was positively and significantly correlated with mammalian cell cytotoxicity, and agreed with 80% of the cytotoxicity rank order. This suggests that the induction of cytotoxicity involved reactions with agents that acted as thiol pool quenchers. The overall results indicate that the cytotoxicity of wastewaters may increase when higher Ct values are applied to inactivate recalcitrant pathogens. To counteract the potential increase in cytotoxicity at high Ct values, for both ozonation and chlorination, lower disinfectant dose and longer contact time may be adopted.

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.

Role of drinking water biofilms on residual chlorine decay and trihalomethane formation: An experimental and modeling study.

PVC pipe loops were constructed to simulate household premise plumbing. These pipe loops were exposed to water treated by physical processes at three water treatment plants in Xiamen, China from August 2016 to June 2017. After the biofilms were allowed to develop inside the pipes, these pipes were deconstructed and exposed to organic-free chlorine solution buffered at pH 6.8 ±â€¯0.2 for 48 h. The decay of chlorine by these biofilms was higher than by the effluent waters that were used to grow the biofilms. A chlorine consumption mass balance model elucidated the role of both the diffusion of chlorine into the biofilm and the reaction of chlorine with the biofilm matrix. Comparable concentrations of trihalomethanes were quantified from the reaction between chlorine and source water organic matters, and chlorine and the biofilm, further emphasizing the role of biofilms in the safety of disinfected drinking water. These findings imply that when chlorine is used in the drinking water distribution system, the ubiquitous presence of biofilms may cause the depletion of chlorine and the formation of non-negligible levels of toxic disinfection byproducts.