Iron particles present in drinking water distribution systems (DWDSs) could cause discoloration, while organic pollutants in DWDSs, such as perfluorooctanoic acid (PFOA), could be enriched by iron particles. However, little is known about the enhanced effects of PFOA and iron particles in DWDSs. To fill in these knowledge gaps, herein, iron-PFOA (FEP) particles were generated using residual chlorine as an oxidant in drinking water conditions and then separated into different sizes (ranging from small to large: FEP-S, FEP-M ，and FEP-L). FEP-S harbored the greatest cytotoxicity among the sizes. Interestingly, our data revealed that the PFOA released from FEP particles transformed into PFOS (perfluorooctane sulfonate) upon digestion in the gastrointestinal environment (GI), and FEP-L bored the strongest transformation, showing a toxicity profile that was distinct from that of FEP-S. Furthermore, mechanistic studies revealed that FEP per se should be accountable for the conversion of PFOA to PFOS dependent on the generation of hydroxyl radicals (·OH) in GI, and that FEP-L revealed the greatest production of ·OH. Collectively, these results showed how iron particles and PFOA could result in enhanced toxicity effects in drinking water: (i) PFOA could increase the toxicity of iron particles by reducing particle size and inducing higher generation of ·OH; (ii) iron particles could induce the transformation of PFOA into more toxic PFOS through digestion.

Silver nanoparticles (AgNPs) are used in many industries for multiple applications that inevitably release AgNPs into surface water sources. The formation kinetics of disinfection by-products (DBPs) in the presence of AgNPs was investigated during chlorination. Experiments were carried out with raw water from a canal in Songkhla, Thailand, which analyzed the formation potential (FP) of trihalomethanes FP (THMFP), iodo-trihalomethanes FP (I-THMFP), haloacetonitriles FP (HANFP), and trichloronitromethane FP. Increased AgNP concentrations by 10–20 mg/L led to a higher specific formation rate of chloroform which is described by zero- and first-order kinetics. The increase in the specific formation of chloroform as increasing chlorine contact time could enhance both the THMFP rates and the maximum THMFP concentrations in all tested AgNPs. The AgNP content did not have a significant influence on I-THMFP and HANFP concentrations or speciation. The I-THMFP and HANFP increased in a short-chlorination time as mostly complete formation <12 h, and then the rate decreased as the reaction proceeded. The levels of THMs and many emerging DBPs are related to the presence of AgNPs in chlorinated water and chlorine reaction time. THMFP had a higher impact on integrated toxic risk value (ITRV) than I-THMFP and HANFP because of the chlorination of water with AgNPs. The chlorine reaction time was more effective for increasing the ITRV of THMFP than the level of AgNPs. Water treatment plants should control the DBPs that cause possible health risks from water consumption by optimizing water distribution time.

Short-chain chlorinated paraffins (SCCPs) are persistent organic pollutants which are toxic to human. Median-chain chlorinated paraffins (MCCPs) have similar toxicity to SCCPs. The productions of chlorinated paraffins (CPs) in China were 1 million tons in 2013 and remained high after that, which may lead to high risks for human exposure to CPs. To investigate temporal trends and health risks of SCCPs and MCCPs in breast milk in China, samples (n = 2020) were collected from urban and rural areas of 11 Chinese provinces in 2017 and mixed into 42 pooled samples. SCCPs and MCCPs were analyzed by two-dimensional gas chromatography with electron-capture negative-ionization mass spectrometry (GC × GC-ECNI-MS). The MCCP concentrations (median (range)) were 472 (94–1714) and 567 (211–1089) ng g⁻¹ lipid in urban and rural areas, respectively, which showed continuously rapidly increasing during 2007–2017. The SCCP concentrations (median (range)) were 393 (131–808) and 525 (139–1543) ng g⁻¹ lipid in urban and rural areas, respectively. The results showed SCCP levels decreased in urban areas between 2007 and 2017. Significant increases in MCCP/SCCP ratios might arise from extensive manufacturing and use of MCCPs. The median estimated dietary intake via breast milk in urban and rural samples were 1230 and 2510 ng kg⁻¹ d⁻¹, respectively, for SCCPs and 2150 and 1890 ng kg⁻¹ d⁻¹, respectively, for MCCPs. Preliminarily risk assessment showed that SCCPs posed a significant health risk to infants via breastfeeding. The high MCCP levels should also be of concern because of continuous growth and negative effect on infants. Correspondence analysis indicated congeners with higher carbon and chlorine numbers in dietary tend to accumulate in breast milk.

Disinfection is considered as a vital step to ensure the supply of clean and safe drinking water. Various approaches are adopted for this purpose; however, chlorination is highly preferred all over the world. This method is opted owing to its several advantages. However, it leads to the formation of certain by-products. These chlorination disinfection by-products (DBPs) are genotoxic, carcinogenic and mutagenic. Still chlorination is being practiced worldwide. Present review gives insights into the occurrence, toxicity and factors affecting the formation of regulated (THMs, HAAs) and emerging DBPs (N-DBPs, HKs, HAs and aromatic DBPs) found in drinking water. Furthermore, remediation techniques used to control DBPs have also been summarized here. Key findings are: (i) concentration of regulated DBPs surpassed the permissible limit in most of the regions, (ii) high chlorine dose, high NOM, more reaction time (up to 3 h) and high temperature (up to 30 °C) enhance the formation of THMs and HAAs, (iii) high pH favors the formation of THMs while low pH is suitable of the formation of HAAs, (iv) high NOM, low temperature, low chlorine dose and moderate pH favors the formation of unstable DBPs (N-DBPs, HKs and HAs), (v) DBPs are toxic not only for humans but for aquatic fauna as well, (vi) membrane technologies, enhanced coagulation and AOPs remove NOM, (vii) adsorption, air stripping and other physical and chemical methods are post-formation approaches (viii) step-wise chlorination is assumed to be an efficient method to reduce DBPs formation without any treatment. Toxicity data revealed that N-DBPs are found to be more toxic than C-DBPs and aromatic DBPs than aliphatic DBPs. In majority of the studies, merely THMs and HAAs have been studied and USEPA has regulated just these two groups. Future studies should focus on emerging DBPs and provide information regarding their regulation.

In this study, municipal solid waste incineration fly ash (MSWIFA) was first washed (pretreatment) with pure water with liquid to solid (L/S) ratio of 2, 3, 6, 10, to understand the removal efficiency of chlorine and sulphate, as well as its consequent ability as alkaline activator for granulated blast furnace slag (GGBFS). Washed MSWIFA was blended with GGBFS at a fixed ratio of 3:7 to examine their impact on mechanical properties, reaction mechanism, microstructure and leaching behavior. The results showed that chlorine in MSWIFA (>70%) can be washed out easily, while the removal of sulphate was largely depended on the L/S. GGBFS can be better activated by a low L/S (e.g. 2) washed-MSWIFA with attaining the compressive strength of 45.2MPa at 28 days. The higher chlorine and sulphate contents retained in the washed-MSWIFA, the higher the total heat release in the activated GGBFS system. Calcium silicate hydrate (C–S–H), ettringite (AFt) and Friedel’s salt were the main hydration products of the activated binders. The rapid formation of AFt was mainly responsible for the 1-day strength development. Large amounts of Friedel’s salts were formed from 1 day to 3 days associated to the inhibition of sulphate, and the presence of C–S–H played the key role in long-term strength development. The leaching test of heavy metals and soluble ions also demonstrated that washed MSWIFA activated GGBFS binders were harmless to the environment.

Bacterial antibiotic resistance (BAR) is profoundly important to human health, but the environmental reservoirs of resistance determinants are poorly understood. BAR of biofilm and tap water were analyzed by using a water distribution simulator where different doses of chlorine and chloramine were used in this study. The results revealed that the disinfectants (≥2 mg/L) suppressed antibiotic resistant bacteria (ARB) in tap water and biofilms, while disinfected water and biofilms had a high relative abundance of ARB. The difference of ARB concentration and ARB percentage between the samples obtained from a disinfected pipeline and a non-disinfected pipeline became smaller over time. Because the water supply system is a unidirectional process, it is unclear how planktonic bacteria in water transfer BAR over time, although biofilm is suspected to play a role in this process. Compared with the biofilm samples without disinfectant, the disinfected biofilm had lower ICC and HPC/ICC percentage, lower AOC and AOC/TOC percentage, indicating that the disinfectant inhibited the bacteria growth in biofilm, and the disinfected biofilm had high proportion of non-culturable bacteria and low biodegradability, which affected BAR in biofilms. High throughput sequencing showed that in biofilms, the relative abundance of genera (uncultured_f_Rhodocyclaceae, Brevundimonas, and Brevibacillus in chlorinated systems, and Brevundimonas, Brevibacillus in chloraminated systems) with multiple antibiotic resistance and high abundance (up to 78.5%), were positively associated with disinfectant concentration and ARB percentage. The major prevalent genera in biofilms were also detected in tap water, suggesting that biofilm growth or biofilm detachment caused by external environmental factors will allow the movement of biofilm clusters with higher ARB concentration and percentage into bulk water, thereby increasing the antibiotic resistance of bacteria in tap water.

Soluble microbial products (SMPs) discharged into rivers from sewage treatment plants may increase the health risk for downstream drinking water by acting as a precursor of DBPs. Biotransformation or biodegradation could alter the characteristics of SMPs and affect the subsequent formation of DBPs. This study observed the relative contribution of chemical fractions in SMPs and explored the biodegradation of each fraction and their effect on disinfection by-products (DBPs) formation in surface water. The hydrophilic acid (HPIA) and hydrophobic acid (HPOA) constituted the major portion of the SMPs, which were dominated by fulvic acid and humic acids. The transphilic acid (TPIA) and hydrophobic bases (HPOB) were relatively minor but it contained a relative substantial portion of protein-like materials in SMPs. TPIA and HPOB produced insignificant amounts of DBP corresponding to 13% and 14% in the original samples, but they were collectively responsible for 50% of the DBPs yield. Much larger amounts of hydrophobic fractions were utilized than hydrophilic fractions after biodegradation. The increase in SUVA values indicating aromatic structures, except for HPOA fraction, was observed after biodegradation. The protein-like materials in both the HPOA and HPIA fractions and polycarboxylate-type humic acid in the HPIA fraction decreased but the enrichment of HPOA (MW > 100 kDa) and TPIA (MW < 1 kDa) was observed after biodegradation. The production of = C–H in HPIA fraction and the appearance of double peak at 1100 cm⁻¹ in TPIA and HPOB fractions occurred after biodegradation. In overall level, microorganisms effectively utilized DBP precursors from HPIA, HPOA and HPOB fractions but increased the DBPs precursors from the TPIA fraction. TPIA and HPOB fractions had higher DBP yield with chlorine but the DBPs yield of HPIA and HPOA changed little after biodegradation.

The humic-like substances were the main organic components in most wastewater (e.g. domestic sewage, toilet wastewater and landfill leachate). Two types of actual humic-like substances (fulvic acid (FA) and biologically treated landfill leachate (BTLL)) were selected to describe the changes in the properties of humic-like substances (complexation ability, aromaticity and mobility) during electrochemical oxidation. Meanwhile, the acute cytotoxicity of FA and BTLL was also tested by acute toxicological test of luminescent bacteria. The results showed that the consumption of coordinating groups such as phenolic groups and hydrogen bonds reduced the complexation ability of FA and BTLL. The functional groups were degraded with the removal order of quinone group, phenolic group and aromatic group, and finally realized the molecular saturation and aromaticity decrease for humic-like substances. The mobility of FA and BTLL was decreased because of the enhancement of hydrophobicity during electrolysis process. Furthermore, the available chlorine produced during electrochemical oxidation was the main acute cytotoxicity substance, therefore, it is necessary to remove it before discharge in order to reduce ecological risks. This study provides a basis for understanding and evaluating the electrochemical degradation process of humic-like substances in detail.

During chlorine disinfection process, reactions between the disinfectant and 17β-estradiol (E2) lead to the formation of halogenated disinfection byproducts (DBPs) which can be a risk to both ecosystem and human health. The degradation and transformation products of E2 in sodium hypochlorite (NaClO) disinfection processes of different water samples were investigated. The reaction kinetics research showed that the degradation rates of E2 were considerably dependent on the initial pH value and the types of water samples. In fresh water, synthetic marine aquaculture water and seawater, the reaction rate constant was 0.133 min−1, 2.067 min−1 and 2.592 min−1, respectively. The reasons for the above phenomena may be due to the different concentrations of bromide ions (Br−) in these three water samples which could promote the reaction between NaClO and E2. Furthermore, Br− could also cause the formation of brominated DBPs (Br-DBPs). The main DBPs, reaction centers and conceivable reaction pathways were explored. Seven halogenated DBPs have been observed including three chlorinated DBPs (Cl-DBPs) and four Br-DBPs. The active sites of E2 were found to be the pentabasic cyclic ring and the ortho position of the phenol moiety as well as C9-C10 position. The identified Cl/Br-DBPs were also confirmed in actual marine aquaculture water from a shrimp pond. The comparison of bio-concentration factors (BCF) values based on calculation of EPI-suite showed that the toxicities of the Br-DBPs were stronger than that of their chloride analogues. The absorbable organic halogens (AOX) analysis also suggested that the DBPs produced in the marine aquaculture water were more toxic than that in the fresh water system.