Relationships between regulated DBPs and emerging DBPs of health concern in U.S. drinking water

Reconsider the burn: The transient effect of a chlorine burn on controlling opportunistic pathogens in a full-scale chloraminated engineered water system

Nitrification is a serious water-quality issue in chloraminated engineered water systems (EWSs). Nitrification is often remediated by a chlorine burn (i.e., a free‑chlorine conversion), a short-term switch from chloramination to chlorination in EWSs. Opportunistic pathogens (OPs) are the dominant infectious agents in EWSs. However, the responses of OPs to a chlorine burn are unknown. This study for the first time assessed how a chlorine burn affected OPs in a full-scale EWS. We determined the impact of a 1.5-month chlorine burn on four dominant OPs (Legionella, Mycobacterium, Pseudomonas, and Vermamoeba vermiformis) in a representative full-scale chloraminated EWS in the United States. Legionella and Mycobacterium were the most abundant OPs. In the water main, the summed concentration of the four OPs during the chlorine burn [3.27 ± 1.58 log10(GCN·L-1); GCN: genome or gene copy number] was lower (p ≤ 0.001) than before the burn [4.83 ± 0.50 log10(GCN·L-1)]. After the burn, the summed concentration increased to 4.27 ± 0.68 log10(GCN·L-1), comparable to before the burn (p > 0.05), indicating a transient effect of the chlorine burn in the water main. At the residential sites, the summed concentrations of the four OPs were comparable (p > 0.05) at 5.50 ± 0.84, 5.27 ± 1.44, and 5.08 ± 0.71 log10(GCN·L-1) before, during, and after the chlorine burn, respectively. Therefore, the chlorine burn was less effective in suppressing OP (re)growth in the premise plumbing. The low effectiveness might be due to more significant water stagnation and disinfectant residual decay in the premise plumbing. Indeed, for the entire sampling period, the total chlorine residual concentration in the premise plumbing (1.8 mg Cl2·L-1) was lower than in the water main (2.4 mg Cl2·L-1). Consequently, for the entire sampling period, the summed concentration of the four OPs in the premise plumbing [5.26 ± 1.08 log10(GCN·L-1)] was significantly higher (p < 0.001) than in the water main [4.04 ± 1.25 log10(GCN·L-1)]. In addition, the chlorine burn substantially increased the levels of disinfection by-products (DBPs) in the water main. Altogether, a chlorine burn is transient or even ineffective in suppressing OP (re)growth but raises DBP concentrations in chloraminated EWSs. Therefore, the practice of chlorine burns to control nitrification should be optimized, reconsidered, or even replaced.

Suppressing Organic Bromine but Promoting Bromate: Is the Ultraviolet/Ozone Process a Double-Edged Sword for the Toxicity of Wastewater to Mammalian Cells?

Brominated byproducts and toxicity generation are critical issues for ozone application to wastewater containing bromide. This study demonstrated that ultraviolet/ozone (UV/O3, 100 mJ/cm2, 1 mg-O3/mg-DOC) reduced the cytotoxicity of wastewater from 14.2 mg of pentol/L produced by ozonation to 4.3 mg of pentol/L (1 mg/L bromide, pH 7.0). The genotoxicity was also reduced from 1.65 to 0.17 μg-4-NQO/L by UV/O3. Compared with that of O3 alone, adsorbable organic bromine was reduced from 25.8 to 5.3 μg/L by UV/O3, but bromate increased from 32.9 to 71.4 μg/L. The UV/O3 process enhanced the removal of pre-existing precursors (highly unsaturated and phenolic compounds and poly aromatic hydrocarbons), while new precursors were generated, yet the combined effect of UV/O3 on precursors did not result in a significant change in toxicity. Instead, UV radiation inhibited HOBr concentration through both rapid O3 decomposition to reduce HOBr production and decomposition of the formed HOBr, thus suppressing the AOBr formation. However, the hydroxyl radical-dominated pathway in UV/O3 led to a significant increase of bromate. Considering both organic bromine and bromate, the UV/O3 process effectively controlled both cytotoxicity and genotoxicity of wastewater to mammalian cells, even though an emphasis should be also placed on managing elevated bromate. Futhermore, other end points are needed to evaluate the toxicity outcomes of the UV/O3 process.

Haloacetamides disinfection by-products, a potential risk factor for nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder characterized by abnormal lipid deposition, with oxidative stress being a risk factor in its onset and progression. Haloacetamides (HAcAms), as unregulated disinfection by-products in drinking water, may alter the incidence and severity of NAFLD through the production of oxidative stress. We explored whether HAcAms at 1, 10, and 100-fold concentrations in Shanghai drinking water perturbed lipid metabolism in normal human liver LO-2 cells. CRISPR/Cas9 was used to construct a LO-2 line with stable NRF2 knock-down (NRF2-KD) to investigate the mechanism underlying abnormal lipid accumulation and hepatocyte damage caused by mixed exposure to HAcAms. At 100-fold real-world concentration, HAcAms caused lipid deposition and increased triglyceride accumulation in LO-2 cells, consistent with altered de novo lipogenesis. Differences in responses to HAcAms in normal and NRF2-KD LO-2 cells indicated that HAcAms caused hepatocyte lipid deposition and triglyceride accumulation by activation of the NRF2/PPARγ pathway and aggravated liver cell toxicity by inducing ferroptosis. These results indicate that HAcAms are important risk factors for NAFLD. Further observations and verifications of the effect of HAcAms on NAFLD in the population are warranted in the future.

Occurrence, bioaccumulation, fate, and risk assessment of emerging pollutants in aquatic environments: A review

Significant concerns on a global scale have been raised in response to the potential adverse impacts of emerging pollutants (EPs) on aquatic creatures. We have carefully reviewed relevant research over the past 10 years. The study focuses on five typical EPs: pharmaceuticals and personal care products (PPCPs), per- and polyfluoroalkyl substances (PFASs), drinking water disinfection byproducts (DBPs), brominated flame retardants (BFRs), and microplastics (MPs). The presence of EPs in the global aquatic environment is source-dependent, with wastewater treatment plants being the main source of EPs. Multiple studies have consistently shown that the final destination of most EPs in the water environment is sludge and sediment. Simultaneously, a number of EPs, such as PFASs, MPs, and BFRs, have long-term environmental transport potential. Some EPs exhibit notable tendencies towards bioaccumulation and biomagnification, while others pose challenges in terms of their degradation within both biological and abiotic treatment processes. The results showed that, in most cases, the ecological risk of EPs in aquatic environments was low, possibly due to potential dilution and degradation. Future research topics should include adding EPs detection items for the aquatic environment, combining pollution, and updating prediction models.

The characteristics of H6 against Microcystis aeruginosa

Algal bloom caused by Microcystis aeruginosa has always been the focus of attention; microbial algal control has the advantages of significant effect, low investment cost, and environmental friendliness; the use of microbial technology to inhibit the bloom has a broad prospect for development. In this study, a strain of Enterobacterium algicidal bacteria screened from a river was used to study the algicidal characteristics against Microcystis aeruginosa using SEM, 3-D EEM and zeta potential. The results showed that the optimal dosage (v/v) of the strain was 5% and the removal rate of algal cells was 70% after 7 days. When the algal density was OD680nm = 0.3, the removal rate of algal cells reached 83% after 7 days. In the pH range of 5 ~ 11, the removal rate of algal cells was 70 ~ 80% after 7 days. Algicidal bacteria H6 is mainly indirect algae lysis and is supplemented by direct algae lysis. Algicidal bacteria H6 removes algicidal substances by secreting high temperature resistant algicidal substances and algicidal products are humic acids. Algicidal bacterium H6 was a strain of Enterobacterium with good algicidal effect in a wide pH range, which enriched the bacterial resources in the control of cyanobacteria bloom in water. The high temperature resistance of the algae-soluble substance secreted by the algae-soluble substance provided convenience for the subsequent preparation and application of bacterial powder.

Impact of prevalent chlorine quenchers on phenolic disinfection byproducts in drinking water and potential reaction mechanisms

To prevent the reactions of disinfection byproducts (DBPs) or natural organic matters with residual chlorine in drinking water in the course of the water store, residual chlorine is quenched by chlorine quenchers, while some chlorine quenchers may result in dechlorination of DBPs. Phenolic compounds are a group of highly toxic DBPs compared to regulated aliphatic DBPs (trihalomethanes (THMs) and haloacetic acids (HAAs)), which might be a great threat to drinking water safety. Nevertheless, impact of popular chlorine quenchers on phenolic DBPs is less understanding. In this study, the influences of ammonium chloride, ascorbic acid, sodium thiosulfate, and sodium sulfite on phenolic DBPs are assessed. Total concentration of 19 phenolic DBPs in drinking water from 7 Chinese cities was 145-1821 ng/L, suggesting a widely occurrence of these pollutants. Four assessed chlorine quenchers have not impacts on mass spectra of studied phenolic DBPs. Additionally, when the storage time ≤24 h, recoveries of 19 phenolic DBPs using four assessed chlorine quenchers are within the accept levels (70-130 %). However, when the storage time increased to 168 h, ascorbic acid and sodium thiosulfate satisfied the recovery requirement of phenolic DBPs during the sample analysis, and ammonium chloride and sodium sulfite showed a unacceptable impact on bromo-chloro-phenols. In general, ascorbic acid and sodium thiosulfate are recommended to be the ideal chlorine quenchers of phenolic DBPs. Mechanism study indicated that sodium sulfite induced the dechlorination of 2-chloro-4-bromophenol via nucleophilic reaction. This study is the first attempt to provide the impact of chlorine quenchers on phenolic DBPs and corresponding reaction mechanism.

Drinking water treatment and associated toxic byproducts: Concurrence and urgence

Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.

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.