•CHO cytotoxicity of HKs were comparable with other priority aliphatic DBPs.•HK cytotoxicity followed the order of mono- > di- > tri-haloHKs.•HKs in drinking water samples of South Carolina and ...Suzhou were 12.4 and 0.9 µg/L.•HKs contributed about 14% of ovearll drinking water cytotoxicity of South Carolina.
Although unregulated aliphatic disinfection byproducts (DBPs) had a much higher concentration and cytotoxicity than known aromatic DBPs, a recent study indicated that seven classes of regulated and unregulated priority DBPs (one and two-carbon-atom DBPs) just accounted for 16.2% of disinfected water cytotoxicity in the U.S., meaning some of the highly toxic aliphatic DBPs may be overlooked. Haloketones (HKs) are an essential class of priority DBPs with a 1–100 µg/L concentration in drinking water but lack cytotoxicity data. This study investigated the cytotoxicity of seven HKs using Chinese hamster ovary (CHO) cells. The order for cytotoxicity of HKs from most to least toxic was: 1,3-dichloroacetone (LC50: 1.0 ± 0.20 μM) ≈ 1,3-dibromoacetone (1.5 ± 0.19 μM) ≈ bromoacetone (1.9 ± 0.49 μM) > chloroacetone (4.3 ± 0.22 μM) > 1,1,3-trichloropropanone (6.6 ± 0.46 μM) > 1,1,1-trichloroacetone (222 ± 7.7 μM) > hexachloroacetone (3269 ± 344 μM). The cytotoxicity of HKs was higher than most regulated and priority aliphatic DBPs in mono-halogenated, di-halogenated, and tri-halogenated categories. A prediction model of HK cytotoxicity was developed based on the quantitative structure-activity relationship (QSAR), optimizing structures and computing descriptors with Gaussian 09 W. The average concentrations of HKs in representative drinking water samples from South Carolina (U.S.) and Suzhou (China) were 12.4 and 0.9 μg/L, respectively, accounting for 18.8% and 1.7% of their specific total DBPs measured (i.e. not TOX). For South Carolina drinking water, their contributions to total calculated additive cytotoxicity of aliphatic DBPs and overall drinking water cytotoxicity were 86.7% and 14.0%, respectively, demonstrating that HKs are an essential class of overlooked DBPs with a high contribution to drinking water cytotoxicity. Our study can help to explain the conflict that why regulated and priority DBPs (except HKs) just accounted for 16% of chlorinated drinking water cytotoxicity even enough they had much higher concentration and cytotoxicity than known aromatic DBPs.
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The alternative disinfectant chloramine can lower the formation of carbonaceous DBPs (C-DBPs) but promote the formation of nitrogenous DBPs (N-DBPs), which are more cytotoxic and genotoxic. In this ...study, the combination of thermally activated persulfate pre-oxidation and post-chloramination (TA/PS-NH2Cl) was proposed to control the formation and reduce the toxicity of both C-DBPs and N-DBPs. The formation, speciation and toxicity of trihalomethanes, haloacetic acids, haloaldehydes, haloacetonitriles, halonitromethanes and haloacetamides, collectively defined as CX3R-type DBPs, under TA/PS-NH2Cl process were compared with processes of chlorination alone (Cl2), chloramination alone (NH2Cl) and coupled thermally activated persulfate pre-oxidation with post-chlorination (TA/PS-Cl2). Results showed that chloramination could reduce formation of C-DBPs and total organic halogen (TOX) while increase N-DBP formation, and the introduction of TA/PS pretreatment process slightly increased the formation of C-DBPs and TOX but sharply reduced the formation of N-DBPs with higher toxicity as well as brominated CX3R-type DBPs that are more toxic than their chlorinated analogues. By comprehensive toxicity calculation, an outright decline of both cytotoxicity and genotoxicity risk of CX3R-type DBPs was observed during TA/PS-NH2Cl process compared with Cl2, NH2Cl, and TA/PS-Cl2 processes. In summary, TA/PS-NH2Cl process was a potential effective method for integrally controlling the formation of CX3R-type DBPs and their toxicity and is suggested to be used to treat raw waters containing no bromide or low levels of bromide considering bromate caused by TA/PS pre-oxidation. The study may provide a feasible and economical method for DBP control on the background of global warming.
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•TA/PS pretreatment increased C-DBPs while decreased N-DBPs during chlor(am)ination.•TA/PS pretreatment clearly/slightly increased TOX during chlorination/chloramination.•TA/PS-NH2Cl decreased the formation of brominated CX3R-type DBPs.•TA/PS-NH2Cl process achieved the lowest cytotoxicity and genotoxicity.
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•The optimal parameters in five disinfection processes were determined.•The amounts of total DBPs followed the order of Cl2 > UV/Cl2 > ClO2 > UV ≈ O3.•The amounts of total DBPFP ...followed the order of UV/Cl2 > UV ≈ Cl2 > O3 > ClO2.•The acute toxicity order of disinfected effluents was Cl2 > UV/Cl2 > ClO2 > UV > O3.•Most of DBPs and DBPFP except TCNMFP were lower in SBTE than those in FPTE.
Hospital wastewater (HWW) contains a large number of pathogenic microorganisms; therefore disinfection is an indispensable unit for its treatment. This study compared the formation and formation potential of disinfection by-products (DBPs) and assessed the variations of acute toxicity for both of first physical treatment effluent (FPTE) and second biological treatment effluent (SBTE) of HWW under five different disinfection processes, including free chlorine (Cl2), chlorine dioxide (ClO2), ozone (O3), ultraviolet (UV) and ultraviolet/chlorine (UV/Cl2). Firstly, the optimal parameters of each disinfection process for FPTE and SBTE were determined respectively based on the required disinfection efficiency (i.e., controlling the concentration of fecal coliforms). The amounts of total DBPs in different disinfection processes under the optimal disinfectants dosage followed the order of Cl2 > UV/Cl2 > ClO2 > UV ≈ O3, which demonstrated that the amount of DBPs formation was closely related to the dosage of chlorine. Meanwhile, the amounts of total disinfection by-products formation potential (DBPFP) under the optimal disinfectants dosage followed the order of UV/Cl2 > UV ≈ Cl2 > O3 > ClO2. Besides, it was found that with the reduction of chlorine dosage, the formed DBPs in UV/Cl2 disinfection process decreased. However, UV/Cl2 disinfection process might degrade organic compounds into more DBPs precursors, leading to higher DBPFP than that in Cl2 disinfection process. Significantly, some specific DBPFPs such as haloketones-FP (HKFP), chloral hydrate-FP (CHFP) and trichloronitromethane-FP (TCNMFP) in O3 disinfection process were found higher than that in Cl2 disinfection process, which could be attributed to the formation of O3 oxidation by-products, for instance aldehydes, methyl ketones and trivalent nitrogen compounds. Additionally, apart from O3, the growth inhibition rate of Chlorella vulgaris increased in all the other disinfection processes and the order of the acute toxicity in each disinfected effluent was consistent with that of DBPs formation.
The effects of UV/H2O2 pre-oxidation or disinfection methods on the formation of partial disinfection by-products (DBPs) have been studied previously. This study assessed the effect of UV/H2O2 ...pre-oxidation combined with optimisation of the disinfection method on the formation of six classes of CX3R-type DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetaldehydes (HALs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloacetamides (HAMs). Experimental results showed that a simulated distribution system (SDS) in-situ chloramination or pre-chlorination followed by chloramination effectively decreased total CX3R-type DBP formation by 51.1–63.5% compared to SDS chlorination, but little reduction in DBP-associated toxicity was observed. The dominant contributors to the calculated toxicity were HANs and HALs. UV/H2O2 pre-oxidation was able to destroy the aromatic and dissolved organic nitrogen components of natural organic matter. As a consequence, THM, HAA, and HAL formations increased by 49.5–55.0%, 47.8–61.9%, and 42.0–67.1%, respectively, whereas HAN, HNM, and HAM formations significantly decreased by 52.1–83.6%, 42.9–87.3%, and 74.1–100.0%. UV/H2O2 pre-oxidation increased total CX3R-type DBP formation, during SDS chlorination, whereas SDS in-situ chloramination or pre-chlorination followed by chloramination of UV/H2O2-treated water produced lower total CX3R-type DBPs than water without UV/H2O2 pre-oxidation. Nevertheless, the DBP-associated toxicity of water with UV/H2O2 pre-oxidation was substantially lower than the toxicity for water without UV/H2O2 pre-oxidation, decreased by 24.1–82.7%. HALs followed by HANs contribute to major toxic potencies in UV/H2O2 treated water. The best DBP concentration and DBP-associated toxicity abatement results were achieved for water treated by UV/H2O2 coupled with in-situ chloramination treatment.
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•In-situ chloramination effectively decreased total concentrations of CX3R-type DBP.•Little change was observed in DBP-associated toxicity under three disinfection processes.•UV/H2O2 pre-oxidation greatly increased C-DBP formation, while it reduced N-DBP formation.•UV/H2O2 pre-oxidation treatment significantly decreased DBP-associated toxicity.•UV/H2O2 coupled with in-situ chloramination lead to the lowest DBP-associated toxicity.
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•The second-order rate constants of TC with OH and SO4− were determined as 4.6 × 109 and 2.2 × 109 M−1 s−1, respectively.•The contributions of UVC photolysis, OH and SO4− to TC ...removal at different pH condtions in UVC/PS process were calculated.•The removal of TC from real waters by UVC and UVC/PS treatment was also desirable.•The degradation pathways were clarified utilizing UPLC-MS/MS analysis and DFT calculation.•UVC and UVC/PS pretreatment could reduce the formation of TCAA and DCAA during post chlorination.
The comparative study on the elimination of tetracycline (TC) utilizing UVC and UVC/PS processes was systematically conducted. The TC degradation via UVC irradiation and UVC/PS treatment well fitted pseudo first-order kinetics. Hydroxyl radicals (OH) and sulfate radicals (SO4−) were identified as the primary reactive species in UVC/PS process. Based on competition kinetic method, the second-order reaction rate constants of TC reacting with OH and SO4− were calculated as 4.6 × 109 and 2.2 × 109 M−1 s−1, respectively. The contributions of UVC photolysis, OH and SO4− to TC degradation were calculated as 5.91%, 61.97% and 28.11% at pH 7.0, respectively. The TC degradation in UVC and UVC/PS process was highly pH-dependent and enhanced with the increase of solution pH. Water matrix constituents played the multiple roles in TC degradation, including radical sensitizer, radical quencher and light absorber. Natural organic matters, CO32– and HCO3– enhanced the degradation during UVC photolysis, whereas the opposite phenomenon occurred in UVC/PS process. Cl− presented the inhibitory effect, while TC degradation can be accelerated by NO3– both in UVC and UVC/PS processes. The TC degradation in UVC/PS process can be classified into the hydroxylation, demethylation, decarbonylation, photocyclinzation, dehydration and cleavage of CN bond. After UVC and UVC/PS pretreatment, the decreased formation of dichloroacetic acid and trichloroacetic acid and the increased production of trichloromethane have been found. The TC removal was evaluated in terms of electrical energy per order, and its value can be considerably reduced via the combination of UVC and PS. Except for ultrapure water, the removal of TC from real waters by UVC/PS treatment could also be desirable.
The comprehensive control efficiency for the formation potentials（FPs） of a range of regulated and unregulated halogenated disinfection by-products（DBPs）（including carbonaceous DBPs（C-DBPs）, ...nitrogenous DBPs（N-DBPs）, and iodinated DBPs（I-DBPs）） with the multiple drinking water treatment processes, including pre-ozonation, conventional treatment（coagulation–sedimentation, pre-sand filtration）, ozone-biological activated carbon（O_3-BAC） advanced treatment, and post-sand filtration, was investigated. The potential toxic risks of DBPs by combing their FPs and toxicity values were also evaluated.The results showed that the multiple drinking water treatment processes had superior performance in removing organic/inorganic precursors and reducing the formation of a range of halogenated DBPs. Therein, ozonation significantly removed bromide and iodide,and thus reduced the formation of brominated and iodinated DBPs. The removal of organic carbon and nitrogen precursors by the conventional treatment processes was substantially improved by O_3-BAC advanced treatment, and thus prevented the formation of chlorinated C-DBPs and N-DBPs. However, BAC filtration leads to the increased formation of brominated C-DBPs and N-DBPs due to the increase of bromide/DOC and bromide/DON.After the whole multiple treatment processes, the rank order for integrated toxic risk values caused by these halogenated DBPs was haloacetonitriles（HANs）》haloacetamides（HAMs） 〉haloacetic acids（HAAs） 〉 trihalomethanes（THMs） 〉 halonitromethanes（HNMs） 》I-DBPs（I-HAMs and I-THMs）. I-DBPs failed to cause high integrated toxic risk because of their very low FPs. The significant higher integrated toxic risk value caused by HANs than other halogenated DBPs cannot be ignored.
Disinfection means the killing of pathogenic organisms (e.g. bacteria and its spores, viruses, protozoa and their cysts, worms, and larvae) present in water to make it potable for other domestic ...works. The substances used in the disinfection of water are known as disinfectants. At municipal level, chlorine (Cl2), chloramines (NH2Cl, NHCl2), chlorine dioxide (ClO2), ozone (O3) and ultraviolet (UV) radiations, are the most commonly used disinfectants. Chlorination, because of its removal efficiency and cost effectiveness, has been widely used as method of disinfection of water. But, disinfection process may add several kinds of disinfection by-products (DBPs) (∼600–700 in numbers) in the treated water such as Trihalomethanes (THM), Haloacetic acids (HAA) etc. which are detrimental to the human beings in terms of cytotoxicity, mutagenicity, teratogenicity and carcinogenicity. In water, THMs and HAAs were observed in the range from 0.138 to 458 μg/L and 0.16–136 μg/L, respectively. Thus, several regulations have been specified by world authorities like WHO, USEPA and Bureau of Indian Standard to protect human health. Some techniques have also been developed to remove the DBPs as well as their precursors from the water. The popular techniques of DBPs removals are adsorption, advance oxidation process, coagulation, membrane based filtration, combined approaches etc. The efficiency of adsorption technique was found up to 90% for DBP removal from the water.
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•Disinfection byproducts have been considered as toxic contaminants of water.•Natural organic matters are the main precursor of DBPs formation in water.•DBPs can cause carcinogenicity, teratogenecity, genotoxicity etc.•GC-ECD is the main determination technique of DBPs in water.•AOPs and adsorption found as the best approaches of DBPs removal from the water.
Disinfection by-products (DBPs) are associated with various adverse health effects. Diversiform advanced treatment processes have been applied for the control of DBPs, but DBPs can still be ...frequently detected in tap water. Tea-leaves can be made into popular beverage and is itself a porous bio-adsorbent. By simulating tea brewing process, this study evaluated the removal of DBPs from drinking water during the tea brewing process. Removal of four trihalomethanes (THMs) and four haloacetamides (HAMs) by different fermentation degree tea-leaves was investigated. Little DBPs were removed by unfermented and semi-fermented tea-leaves (i.e., Meitan turquoise bud and Dahongpao tea) with less than 5% removal of HAMs, whereas 40% HAMs can be removed by fermented tea (i.e., Jinjunmei tea and Shuixian tea). Tea soup is neutral and slightly acidic, so little DBP hydrolysis was observed under typical tea-leaf brewing process. DBPs were mainly removed by volatilization and adsorption during tea brewing. Removal difference caused by DBP volatilization is very small. The DBP removal difference of four kinds of tea-leaves may be caused by fermentation degree. The surface of unfermented Meitan turquoise bud had a smooth and regular morphology, whereas a rough, irregular, hollow and spongy surface of fermented tea (i.e., Jinjunmei and Shuixian tea) was observed. Generally, the higher the degree of tea fermentation, the more adsorption sites, and the more removal of DBPs. Finally, the model, which takes the DBP initial concentration, tea-leaf dose and brewing time into account, was established under the experimental conditions to predict the variation of DBP concentration during tea brewing, and suggestions for DBP removal were provided to reduce DBP exposure risk. The integrated toxic risk during tea brewing was also investigated, and about 30% integrated cytotoxicity and 26% genotoxicity was reduced during Jinjunmei and Shuixian tea-leaf brewing.
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•THMs and HAMs were reduced by volatilization and adsorption during tea-leaf brewing.•DBP adsorption was related with tea-leaf fermentation degree.•The higher the tea-leaf fermentation degree, the more adsorption sites.•Mathematic model can be used to predict the decrease of THMs and HAMs.
Sex and thyroid hormones are critical for male reproductive health. However, the associations between haloacetic acid (HAA) exposure – a known endocrine disruptor – and sex and thyroid hormones in ...humans remains unclear. We thus recruited 502 male participants seeking fertility evaluation from a reproductive center. We measured concentrations of sex and thyroid hormones in a single blood sample and dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in repeated urine samples. Multivariable linear regression models were constructed to evaluate the associations between HAA concentrations and hormone measurements. After adjusting for potential confounders and urinary creatinine concentrations, urinary concentrations of TCAA were inversely associated with serum levels of sex hormone-binding globulin (SHBG), testosterone (T), T/luteinizing hormone ratio (T/LH), and thyroid stimulating hormone (TSH) (all P for trend < 0.10). Compared with participants in the lowest quartile of TCAA concentrations, those in the highest quartile had reduced serum levels of SHGB by 14.2 % (95% CI: −26.7, −3.0 %), T by 11.1 % (95% CI: −21.7, −1.3 %), T/LH by 21.0 % (95% CI: −36.7, −7.1 %), and TSH by 19.1 % (95% CI: −39.7, −1.5 %). Additionally, we observed inverse associations between continuous measurements of urinary HAAs and serum levels of free T, bioactive T, and estradiol. Our findings suggest that male HAA exposure may be associated with disrupted sex and thyroid function.
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•CX3R-type DBP formation is compared between PMS/Cl− and NaClO disinfection.•CX3R-type DBP level in PMS/Cl− is lower than that in NaClO disinfection.•DBP formation pathway during ...PMS/Cl− disinfection is proposed.•The cytotoxicity from DBPs in PMS/Cl− is lower than that in NaClO disinfection.
Peroxymonosulfate (PMS) is receiving increasing interest as an oxidant used during the disinfection of drinking water. However, it does not have continuous disinfection ability as sodium hypochlorite (NaClO) does. PMS/Cl− can produce reactive chlorine species and thus provide a persistent disinfectant residual in distribution systems. This study investigated PMS/Cl− disinfection versus NaClO disinfection in terms of the formation and estimated cytotoxicity of CX3R-type disinfection by-products (DBPs) under the same dose of free chorine. Results showed that free chlorine produced by PMS/Cl− reaction can react with organic compounds and the productions of CX3R-type DBPs were dependent on the free chlorine dose, pH and reaction time. Specifically, chloroform (CF) and chloral hydrate (CH) generally increased with increasing of free chlorine dose and reaction time. CF increased steadily with increasing pH, while CH firstly increased and then decreased with increasing pH. Haloacetonitriles and haloacetamides firstly increased and then decreased with increasing of free chlorine dose and reaction time, and decreased continuously with increasing pH. The formation pathway of CX3R-type DBPs during chlorination (PMS/Cl−) of tyrosine was proposed, based on the detected intermediates (i.e., Benzyl cyanide, 4-hydroxy-benzyl-cyanide, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol). The estimated cytotoxicity of CX3R-type DBPs in chlorinated water firstly increased and then decreased with the increasing of reaction time, free chlorine dose and pH, which highly related to the changes of DCAN (the most toxic CX3R-type DBP) levels. Comparing to NaClO disinfection, PMS/Cl− disinfection can better control the formation and cytotoxicity of CX3R-type DBPs, which was attributed to the degradation of natural organic matter, CX3R-type DBPs intermediates and CX3R-type DBPs by the residual PMS. This study demonstrated the superiority of PMS/Cl− as an alternative disinfectant comparing to NaClO.
