Toxicity evaluation of surface water treated with different disinfectants in HepG2 cells

Comparative evaluation of SPE methods for biotoxicity assessment of water and wastewater: Linkage between chemical extracting efficiency and biotoxicity outcome

Biotoxicity assessment results of environmental waters largely depend on the sample extraction protocols that enrich pollutants to meet the effect-trigger thresholds of bioassays. However, more chemical mixture does not necessarily translate to higher combined biotoxicity. Thus, there is a need to establish the link between chemical extracting efficiency and biotoxicity outcome to standardize extraction methods for biotoxicity assessment of environmental waters. This study compares the performance of five different extraction phases in solid phase extraction (SPE), namely HLB, HLB+Coconut, C18 cartridge, C18 disk and Strata-X, and evaluated their chemical extracting efficiencies and biotoxicity outcomes. We quantitatively assessed cytotoxicity, acute toxicity, genotoxicity, estrogenic activity, and neurotoxicity of the extracts using in vitro bioassays and characterized the chemical extracting efficiencies of the SPE methods through chemical recoveries of 23 model compounds with different polarities and total organic carbon. Using Pareto ranking, we identified HLB+Coconut as the optimal SPE method, which exhibited the highest level of water sample biotoxicity and recovered the most chemicals in water samples. We found that the biotoxicity outcomes of the extracted water samples significantly and positively correlated with the chemical extracting efficiencies of the SPE methods. Moreover, we observed synchronous changing patterns in biotoxicity outcome and chemical extracting efficiencies in response to increasing sample volumes per cartridge (SVPC) during SPE. Our findings underscore that higher chemical extracting efficiency of SPE corresponds to higher biotoxicity outcome of environmental water samples, providing a scientific basis for standardization of SPE methods for adequate assessment of biotoxicities of environmental waters.

Stability of Drinking Water Distribution Systems and Control of Disinfection By-Products

The stability of drinking water distribution systems and the management of disinfection by-products are critical to ensuring public health safety. In this paper, the interrelationships between corrosion products in the network, microbes, and drinking water quality are elucidated. This review also discusses the mechanisms through which corrosive by-products from the piping network influence the decay of disinfectants and the formation of harmful disinfection by-products. Factors such as copper corrosion by-products, CuO, Cu₂O, and Cu²⁺ play a significant role in accelerating disinfectant decay and catalyzing the production of by-products. Biofilms on pipe walls react with residual chlorine, leading to the formation of disinfection by-products (DBPs) that also amplify health risks. Finally, this paper finally highlights the potential of peroxymonosulfate (PMS), an industrial oxidant, as a disinfectant that can reduce DBP formation, while acknowledging the risks associated with its corrosive nature. Overall, the impact of the corrosive by-products of pipe scale and microbial communities on water quality in pipe networks is discussed, and recommendations for removing DBPs are presented.

Occurrence and Cytotoxicity of Aliphatic and Aromatic Halogenated Disinfection Byproducts in Indoor Swimming Pool Water and Their Incoming Tap Water

Disinfection byproducts (DBPs) in swimming pool water are of wide concern for public health. In this study, the occurrence of five categories of aliphatic halogenated DBPs, i.e., trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), halonitromethanes (HNMs), and haloketones (HKs), and six categories of aromatic halogenated DBPs, i.e., halophenols (HPs), halonitrophenols (HNPs), halohydroxy-benzaldehydes (HBALs), halohydroxybenzoic acids (HBAs), halobenzoquinones (HBQs), and haloanilines (HAs), was examined in seven indoor swimming pool water and their incoming tap water. The correlations between the DBP concentrations and water quality parameters were explored. Moreover, the cytotoxicity of the aliphatic and aromatic halogenated DBPs was tested with human hepatoma (HepG2) cells, and the concentration-cytotoxicity contributions of different DBP categories were calculated. The results demonstrate that 24 aliphatic (5 THMs, 8 HAAs, 5 HANs, 4 HNMs, and 2 HKs) and 50 aromatic halogenated DBPs (9 HPs, 8 HNPs, 9 HBALs, 8 HBAs, 11 HBQs, and 5 HAs) were present in the swimming pool water, among which 41 aromatic halogenated DBPs were detected in swimming pool water for the first time. The average concentrations of the five categories of aliphatic halogenated DBPs in the swimming pool water were in the order of HAAs > HANs > HKs > THMs > HNMs, while those in their incoming tap water were in the order of THMs > HAAs > HKs > HANs > HNMs. The average concentrations of the aromatic halogenated DBPs in the swimming pool water were significantly lower than those of the aliphatic halogenated DBPs, following the order of HBQs > HPs > HBAs > HBALs > HAs > HNPs, while those in their incoming tap water were in the order of HBALs > HBQs > HPs > HBAs > HAs > HNPs. The average concentration-cytotoxicity contributions of different DBP categories in the swimming pool water followed the order of HAAs > HANs > HNMs > HKs > HBQs > THMs > HPs > HNPs > HBAs > HBALs > HAs, with HAAs, HANs, and HNMs possessing the main concentration-cytotoxicity contributions (93.2% in total) among all DBP categories.

NRF2-ARE signaling is responsive to haloacetonitrile-induced oxidative stress in human keratinocytes

Humans are exposed to disinfection by-products through oral, inhalation, and dermal routes, during bathing and swimming, potentially causing skin lesions, asthma, and bladder cancer. Nuclear factor E2-related factor 2 (NRF2) is a master regulator of the adaptive antioxidant response via the antioxidant reaction elements (ARE) orchestrating the transcription of a large group of antioxidant and detoxification genes. Here we used an immortalized human keratinocyte model HaCaT cells to investigate NRF2-ARE as a responder and protector in the acute cytotoxicity of seven haloacetonitriles (HANs), including chloroacetonitrile (CAN), bromoacetonitrile (BAN), iodoacetonitrile (IAN), bromochloroacetonitrile (BCAN), dichloroacetonitrile (DCAN), dibromoacetonitrile (DBAN), and trichloroacetonitrile (TCAN) found in drinking water and swimming pools. The rank order of cytotoxicity among the HANs tested was IAN ≈ BAN ˃ DBAN ˃ BCAN ˃ CAN ˃ TCAN ˃ DCAN based on their LC₅₀. The HANs induced intracellular reactive oxygen species accumulation and activated cellular antioxidant responses in concentration- and time-dependent fashions, showing elevated NRF2 protein levels and ARE activity, induction of antioxidant genes, and increased glutathione levels. Additionally, knockdown of NRF2 by lentiviral shRNAs sensitized the HaCaT cells to HANs-induced cytotoxicity, emphasizing a protective role of NRF2 against the cytotoxicity of HANs. These results indicate that HANs cause oxidative stress and activate NRF2-ARE-mediated antioxidant response, which in turn protects the cells from HANs-induced cytotoxicity, highlighting that NRF2-ARE activity could be a sensitive indicator to identify and characterize the oxidative stress induced by HANs and other environmental pollutants.

Acute Toxicity Evaluation of the Disinfectant Containing Percarbonate and Tetraacetylethylenediamine by Measuring Behavioral Responses of Small Fish Using Image Analysis

Disinfectants containing percarbonate and tetraacetylethylenediamine (TAED) has been developed as an effective and relatively safe disinfectant to destroy viruses and bacteria in animals and humans, however it is known that most disinfectants can cause danger to living organisms including humans. In the current study, acute toxicity of the disinfectant composed of percarbonate and TAED was assessed by measuring behavioral responses as well as lethal concentrations of aquatic organisms such as medaka and zebrafish when they were exposed to it. First, the breeding water properties were determined by measuring dissolved oxygen (DO) and pH changes over time up to 96 h in acute toxicity tests using the medaka, and the lethal concentration 50% (LC50, 88.39 ppm) was calculated using the lethality rate of the fish. This experiment was conducted in compliance with traditional OECD guidelines. Second, the assessment of behavioral responses (locomotive activity and swimming speed) with the zebrafish were assessed by the image analysis to capture the images per second for three hours, and the collected data were processed using image analysis to calculate the locomotive activity and swimming speed. Finally, the LC50 (135.76 ppm) of the disinfectant to the fish was also measured after three hours. Overall, the data revealed that LC50 of the disinfectant may be affected by the pH of the water exposed to the disinfectant, not by the DO in the water. In addition, the results from the image analysis indicated that the behavioral responses of the fish can further assess the acute toxicity of the disinfectant at concentrations below the LC50 and there was a relationship (R² = 0.85) between the behavioral responses and the survival rate of the fish.

Metabonomic and transcriptomic modulations of HepG2 cells induced by the CuO-catalyzed formation of disinfection byproducts from biofilm extracellular polymeric substances in copper pipes

Cupric oxide (CuO) is able to catalyze the reactions among disinfectant, extracellular polymeric substances (EPS) and bromide (Br^-) in copper pipes, which may deteriorate the water quality. This study aimed to investigate the metabonomic and transcriptomic modulations of HepG2 cells caused by the CuO-catalyzed formation of disinfection byproducts (DBPs) from EPS. The presence of CuO favored the substitution reactions of chlorine and bromine with EPS, inducing a higher content of total organic halogen (TOX). In addition, DBPs were shifted from chlorinated species to brominated species. A total of 182 differential metabolites (DMs) and 437 differentially expressed genes (DEGs) were identified, which were jointly involved in 38 KEGG pathways. Topology analysis indicates that glycerophospholipid and purine metabolism were disturbed most obviously. During glycerophospholipid metabolism, the differential expression of genes GPATs, AGPATs, LPINs and DGKs impacted the conversion of glycerol-3-phosphate to 2-diacyl-sn-glycerol, which further affected the conversion among phosphatidylcholine, phosphatidylserine and phosphocholines. During purine metabolism, it was mainly the differential expression of genes POLRs, RPAs, RPBs, RPCs, ENTPDs and CDs that impacted the transformation of RNA into guanine-, xanthosine-, inosine- and adenosine monophosphate, which were further successively transformed into their corresponding nucleosides and purines. The study provides an omics perspective to assess the potential adverse effects of overall DBPs formed in copper pipes on human.

Identification, formation and control of polar brominated disinfection byproducts during cooking with edible salt, organic matter and simulated tap water

Edible salt is essential to the health of humans and serves as a seasoning universally. Besides chloride, edible salt also contains other anions such as bromide, fluoride, sulfate, and carbonate due to incomplete removal during raw salt refinement. In a household cooking (e.g., soup making) process, a chlorine/monochloramine residual in tap water could react with bromide in edible salt and organic matter in food (e.g., rice, wheat) to form numerous brominated disinfection byproducts (Br-DBPs) at significant levels, which might induce adverse health effects to human beings. In this study, we solicited 20 edible salts of different types (i.e., sea salts, well and rock salts, lake salts, and bamboo salts) from nine countries and determined their bromide levels to be 67-375 mg/kg, with an average level of 173 mg/kg. A total of 25 polar Br-DBPs were detected and identified with structures/formulae in cooking water samples using ultra performance liquid chromatography/electrospray ionization-triple quadruple mass spectrometry (UPLC/ESI-tqMS) and high-resolution mass spectrometry. Effects of cooking conditions (e.g., disinfectant type and level, edible salt dose, organic matter type and dose, sequence and time interval of adding organic matter and salt, etc.) on the formation of polar Br-DBPs were investigated, and optimized cooking conditions with minimized formation of polar Br-DBPs were determined. Further aided with an Hep G2 cell cytotoxicity assay, it was found that the overall cytotoxicity of chlorinated and chloraminated cooking water samples prepared after cooking condition optimization was reduced by 57% and 22%, respectively, compared with those prepared before cooking condition optimization.

Disinfection by-products formation and ecotoxicological effects of effluents treated with peracetic acid: A review

Peracetic acid (PAA) has gained increasing attention over the last decades as a suitable and environmentally-friendly alternative to chlorine-based compounds for wastewater disinfection, claiming limited disinfection by-products (DBPs) formed and no persistent residues in the environment. The present work aims at presenting a comprehensive and updated review of the ecotoxicological effects of effluents treated with PAA, to be ascribed to residual PAA and hydrogen peroxide (H₂O₂) and DBP formation. Modest concentrations of DBPs have been observed after PAA treatment, mainly carboxylic acids, which are not recognized as genotoxic. Moreover, there is no evidence of any endocrine disruption potential of PAA in human health or in the ecotoxicological studies. The associated H₂O₂ fraction can potentially minimize the formation of halogenated DBPs and also contribute to the acute toxic effects of treated effluents. Effluents disinfected with PAA at concentrations typical of the wastewater treatment field have displayed limited toxic, mutagenic and genotoxic effects on different aquatic organisms, particularly low compared to chlorine-based disinfectants.

Polyphenols from the extract and fraction of T. indica seeds protected HepG2 cells against oxidative stress

Background

Tamarindus indica L. (T. indica) or locally known as “asam jawa” belongs to the family Leguminosae. T. indica seeds as by-products from the fruits were previously reported to contain high polyphenolic content. However, identification of their bioactive polyphenols using recent technologies is less well researched but nonetheless important. Hence, it was the aim of this study to provide further information on the polyphenolic content and antioxidant activities as well as to identify and quantify its bioactive polyphenols.

Methods

T. indica seeds were extracted with methanol and were then fractionated with different compositions of hexane, ethyl acetate and methanol. Polyphenolic contents were measured using Folin-Ciocalteu assay while antioxidant activities were measured using DPPH radical scavenging and ferric reducing (FRAP) activities. The cytotoxic activities of the crude extract and the active fraction were evaluated in HepG2 cells using MTT assay. The cells were then pre-treated with the IC₂₀ concentrations and induced with H₂O₂ before measuring their cellular antioxidant activities including FRAP, DPPH, lipid peroxidation, ROS generation and antioxidant enzymes, SOD, GPx and CAT. Analyses of polyphenols in the crude extract and its active fraction were done using UHPLC and NMR.

Results

Amongst the 7 isolated fractions, fraction F3 showed the highest polyphenolic content and antioxidant activities. When HepG2 cells were treated with fraction F3 or the crude extract, the former demonstrated higher antioxidant activities. F3 also showed stronger inhibition of lipid peroxidation and ROS generation, and enhanced activities of SOD, GPx and CAT of HepG2 cells following H₂O₂-induced oxidative damage. UHPLC analyses revealed the presence of catechin, procyanidin B2, caffeic acid, ferulic acid, chloramphenicol, myricetin, morin, quercetin, apigenin and kaempferol, in the crude seed extract of T. indica. UHPLC and NMR analyses identified the presence of caffeic acid in fraction F3. Our studies were the first to report caffeic acid as the active polyphenol isolated from T. indica seeds which likely contributed to the potent antioxidant defense system of HepG2 cells.

Conclusion

Results from this study indicate that caffeic acid together with other polyphenols in T. indica seeds can enhance the antioxidant activities of treated HepG2 cells which can provide protection against oxidative damage.

Evidence of ATP assay as an appropriate alternative of MTT assay for cytotoxicity of secondary effluents from WWTPs

Biological tests are effective and comprehensive methods to assess toxicity of environmental pollutants to ensure the safety of reclaimed water. In this study, the canonical MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was performed to evaluate the cytotoxicity of dissolved organic matters (DOMs) of secondary effluents from wastewater treatment plants (WWTPs). It was surprising that most concentrated DOMs treated HepG2 cells yielded much higher signal compared with vehicle control regardless of difference of treatment technologies and seasons. However, there was actually no obvious enhancement of the cell proliferation by microscopy. In order to find out potential reason for the discrepancy, another three assays were performed. The results of ATP assay and flow cytometry showed expected toxicity, which was consistent with microscopy and previous studies, while DNA assay did not exhibit apparent change in treated cells. The possible mechanisms of abnormal MTT signal could be that some materials in secondary effluents isolated by solid extraction with HLB resin directly reacted with MTT and/or enhanced the activity of mitochondrial dehydrogenase. Therefore, the MTT assay is not suitable to assess cytotoxicity of complex mixtures such as secondary effluents, while ATP assay is an optional sensitive method. This study also suggests the importance of choosing both suitable extraction methods and detection assays for toxicity evaluation of component-unknown environmental samples.

Investigation into the effects of antioxidant-rich extract of Tamarindus indica leaf on antioxidant enzyme activities, oxidative stress and gene expression profiles in HepG2 cells

The leaf extract of Tamarindus indica L. (T. indica) had been reported to possess high phenolic content and showed high antioxidant activities. In this study, the effects of the antioxidant-rich leaf extract of the T. indica on lipid peroxidation, antioxidant enzyme activities, H₂O₂-induced ROS production and gene expression patterns were investigated in liver HepG2 cells. Lipid peroxidation and ROS production were inhibited and the activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase was enhanced when the cells were treated with the antioxidant-rich leaf extract. cDNA microarray analysis revealed that 207 genes were significantly regulated by at least 1.5-fold (p < 0.05) in cells treated with the antioxidant-rich leaf extract. The expression of KNG1, SERPINC1, SERPIND1, SERPINE1, FGG, FGA, MVK, DHCR24, CYP24A1, ALDH6A1, EPHX1 and LEAP2 were amongst the highly regulated. When the significantly regulated genes were analyzed using Ingenuity Pathway Analysis software, “Lipid Metabolism, Small Molecule Biochemistry, Hematological Disease” was the top biological network affected by the leaf extract, with a score of 36. The top predicted canonical pathway affected by the leaf extract was the coagulation system (P < 2.80 × 10⁻⁶) followed by the superpathway of cholesterol biosynthesis (P < 2.17 × 10⁻⁴), intrinsic prothrombin pathway (P < 2.92 × 10⁻⁴), Immune Protection/Antimicrobial Response (P < 2.28 × 10⁻³) and xenobiotic metabolism signaling (P < 2.41 × 10⁻³). The antioxidant-rich leaf extract of T. indica also altered the expression of proteins that are involved in the Coagulation System and the Intrinsic Prothrombin Activation Pathway (KNG1, SERPINE1, FGG), Superpathway of Cholesterol Biosynthesis (MVK), Immune protection/antimicrobial response (IFNGR1, LEAP2, ANXA3 and MX1) and Xenobiotic Metabolism Signaling (ALDH6A1, ADH6). In conclusion, the antioxidant-rich leaf extract of T. indica inhibited lipid peroxidation and ROS production, enhanced antioxidant enzyme activities and significantly regulated the expression of genes and proteins involved with consequential impact on the coagulation system, cholesterol biosynthesis, xenobiotic metabolism signaling and antimicrobial response.

Chemical and bioanalytical assessments on drinking water treatments by quaternized magnetic microspheres

This study aimed to compare the toxicity reduction performance of conventional drinking water treatment (CT) and a treatment (NT) with quaternized magnetic microspheres (NDMP) based on chemical analyses. Fluorescence excitation-emission-matrix combined with parallel factor analysis identified four components in source water of different rivers or lake, and the abundance of each component differed greatly among the different samples. Compared with the CT, the NT evidently reduced the concentrations of dissolved organic carbon, adsorbable organic halogens (AOX), bromide and disinfection by-products. Toxicological evaluation indicated that the NT completely eliminated the cytotoxicity, and greatly reduced the genotoxicity and oxidative stress of all raw water. In contrast, the CT increased the cytotoxicity of Taihu Lake and the Zhongshan River water, genotoxicity of Taihu Lake and the Mangshe River water, as well as the levels of superoxide dismutase and malondialdehyde of the Mangshe River water. Correlation analysis indicated that the AOX of the treated samples was significantly correlated with the genotoxicity and glutathione concentration, but exhibited no correlation with either of them for all the samples. As it can effectively reduce pollutant levels and the toxicities of drinking water, NDMP might be widely used for drinking water treatment in future.

Toxicity assessment of chlorinated wastewater effluents by using transcriptome-based bioassays and Fourier transform mass spectrometry (FT-MS) analysis

Effects of chlorination on the toxicity of wastewater effluents treated by activated sludge (AS) and submerged membrane bioreactor (S-MBRB) systems to HepG2 human hepatoblastoma cells were investigated. In addition to the cytotoxicity and genotoxicity assays, the DNA microarray-based transcriptome analysis was performed to evaluate the change in types of biological impacts on HepG2 cells of the effluents by chlorination. Effluent organic matter (EfOM) and disinfection by-products (DBPs) were also characterized by using Fourier transform mass spectrometry (FT-MS). Although no significant induction of genotoxicity was observed by chlorination for both effluents, the chlorination elevated the cytotoxicity of AS effluent but reduced that of S-MBRB effluent. The FT-MS analyses revealed that more DBPs including nitrogenated DBPs (N-DBPs) were formed in the AS effluent than in the S-MBRB effluent by chlorination, supporting the increased cytotoxicity of AS effluent. The lower O/C ratio of S-MBRB EfOM suggests that a large number of organic molecules were detoxified by chlorination, which consequently decreased the cytotoxicity of S-MBRB effluent. Integration of all the results highlights that both cytotoxicity and biological impacts of chlorinated wastewater effluents were clearly dependent on the EfOM characteristics such as DBPs and O/C ratio, namely, on types of treatment systems.

Water quality assessment using the AREc32 reporter gene assay indicative of the oxidative stress response pathway

The reporter gene assay AREc32 is based on the induction of the Nrf2 mediated oxidative stress response pathway in the human breast cancer cell line MCF7, where eight copies of the antioxidant response element (ARE) are linked to a reporter gene encoding for luciferase. The Nrf2-ARE pathway is responsive to many chemicals that cause oxidative stress, among them a large number of pesticides and skin irritants. We adopted and validated the AREc32 bioassay for water quality testing. tert-Butylhydroquinone served as the positive control, phenol as the negative control and other reactive chemicals were assessed for their specificity. An environmentally relevant reference chemical, benzo(a)pyrene was the most potent inducer of all tested chemicals. The concentration causing an induction ratio (IR) of 1.5 (EC(IR1.5)) was chosen as the effect benchmark value. The assay was applied to 21 water samples ranging from sewage to drinking water, including secondary treatment and various tertiary treatment options (ozonation, biologically activated carbon filtration, membrane filtration, reverse osmosis, advanced oxidation, chlorination, chloramination). The samples were enriched by solid phase extraction. In most samples the oxidative stress response was far more sensitive than cytotoxicity. The primary and secondary treated effluent exceeded the effect threshold IR 1.5 at a relative enrichment factor (REF) of 1, i.e., the native samples were active. All tertiary treated samples were less potent and their EC(IR1.5) lay between REF 1 and 10. The Nrf2 pathway was induced at a REF of approximately 10 for surface waters and drinking water, and above this enrichment cytotoxicity took over in most samples and quenched the induction. The blank (ultrapure water run through the sample enrichment process) was cytotoxic at an REF of 100, which is the limit of concentrations range that can be evaluated. Treatment typically decreased both the cytotoxicity and oxidative stress response apart from drinking water treatment where chlorination caused an increase in oxidative stress response, presumably due to the formation of disinfection by-products. This study demonstrates the relevance and applicability of the oxidative stress response pathway for water quality monitoring.

The effects of subacute exposure of peracetic Acid on lipid peroxidation and hepatic enzymes in wistar rats

OBJECTIVES

This study was undertaken to determine the effect of subacute exposure of peracetic acid on lipid peroxidation and hepatic enzymes in Wistar rats.

METHODS

48 male animals in Treatment Group I, II and III received 0.2%, 2% and 20% peracetic acid daily for 2 and 4 weeks.

RESULTS

Serum malondialdehyde increased and Alanine Transaminase and Aspartate Transaminase decreased significantly in groups 2 and 3, compared to the control group. The malondialdehyde, Alanine Transaminase and Aspartate Transaminase with 0.2% and 2% doses of peracetic acid for 2 weeks do not lead to the alteration of malondialdehyde and enzyme activities.

CONCLUSION

This study demonstrated that the enhancement of malondialdehyde could provide an oxidative damage induced by disinfectant peroxidation at 20% and 2% doses at 2 and 4 weeks. The consumption of peroxidation with 20% for 2 weeks and 2% for 4 weeks can cause the increase of malondialdehyde and the decrease of enzyme activities, respectively.

Algal-derived organic matter as precursors of disinfection by-products and mutagens upon chlorination

Algal-derived organic materials (including algal cells, hydrophilic and hydrophobic proteins) from Chlamydomonas sp. (a common green alga in local reservoirs), were chlorinated in the laboratory (20 °C, pH 7, Cl(2)/DOC ratio of 20 mg Cl(2) mg(-1)). Levels of disinfection by-products and mutagenicity (via Salmonella T100 mutation assay, -S9) over 2 h of chlorination time were determined. The hydrophilic proteins were more effective precursors of chloroform (35.9 μmol L(-1) at 120 min), 35 times greater than that from the hydrophobic proteins; whereas the hydrophobic proteins were more potent precursors of direct-acting mutagens (maximum level of 50.1 rev μL(-1) at 30 s) than the hydrophilic proteins (maximum level of 3.38 rev μL(-1) at 60 min). The mutagenicity of the chlorinated solutions generally reached a peak level shortly after chlorination and then declined afterwards, a pattern different from that of chloroform generation. The results indicate that algal hydrophilic proteins, containing low aromaticity and difficult to be removed via coagulation/flocculation, are important chloroform precursors. It is also suggested that hydrophobic organic intermediates with low molecular weight formed during chlorination may serve as the direct-acting mutagens.

In vitro toxicity of surface water disinfected by different sequential treatments

The in vitro toxicity of extracts of Hanjiang water disinfected by different sequential treatments was evaluated. Hanjiang water was disinfected using ozone, chloride dioxide or chlorine as the primary disinfectant followed by chlorine as the secondary disinfectant. HepG(2) cells were exposed to extracts corresponding to concentrations of 0.2, 1, 5, 25 and 125 mL water/mL medium. Compared with control, HepG(2) cells exposed to extracts of raw water and all disinfected water for 24h increased oxidative stress level, DNA damage and micronuclei frequency, and decreased cell viability. Water disinfected by Cl(2)+Cl(2) had the highest DNA double-strand breaks. All disinfected water and raw water increased micronuclei frequency via clastogenic and aneugenic effects. Oxidative stress induced DNA strand breaks and micronuclei frequency and therefore reduced cell viability either in disinfected water or raw water. Compared with raw water, water after disinfection increased DNA strand breaks, decreased cell viability and changed oxidative stress potential. Compared with chlorination, sequential treatment using O(3) or ClO(2) as primary disinfectant followed by chlorine disinfection reduced chlorinated by-products, DNA double-strand breaks and cell viability, but did not decrease micronuclei frequency and other DNA damage such as DNA single-strand break, alkali liable sites and incomplete excision sites. Sequential treatments did not significantly reduce in vivo toxicity of disinfected Hanjiang water.

Study of the combined effects of a peracetic acid-based disinfectant and surfactants contained in hospital effluents on Daphnia magna

Hospital effluents cause environmental problems since they are 5-15 more toxic than urban effluents and they are not subjected to any pre-treatment before being discharged into urban sewage networks. The hypothesis used to explain this toxicity is the presence of disinfectants and detergents. This study is aimed at highlighting the ecotoxicity of a peracetic acid-based disinfectant to Daphnia magna, as well as the combined effects of this disinfectant in binary mixtures with three types of detergent. The detergents used here are: cetyltrimethylammonium bromide (CTAB, cationic), sodium dodecylsulfate (SDS, anionic) and Triton X-100 (TX, non-ionic). The toxicity of the mixtures is studied as a function of five predefined ratios. At the end of the study, we conclude that peracetic acid seems to be slightly toxic to Daphnia magna. Indeed, the efficient concentration inhibiting the mobility of 50% of the population of Daphnia at 24 h (EC50) is 116.6 mg/l. Globally, additive effects are observed for all the binary peracetic acid-detergent mixtures. However, for the peracetic acid-TX mixture, its effects have antagonistic tendencies whereas the peracetic acid-CTAB mixture has slight synergic tendencies. The mixture containing peracetic acid and SDS is slightly antagonistic for ratios containing more than 50% peracetic acid.