Category Archives: Disinfection Byproducts

Prioritizing unregulated disinfection byproducts for risk mitigation, Canadian Perspective

Mian HR, Hu G, Hewage K, Rodriguez MJ, Sadiq R. Prioritization of unregulated disinfection by-products in drinking water distribution systems for human health risk mitigation: A critical review. Water Res. 2018 Sep 29;147:112-131. doi: 10.1016/j.watres.2018.09.054

Water disinfection involves the use of different types of disinfectants, which are oxidizing agents that react with natural organic matter (NOM) to form disinfection by-products (DBPs). The United States Environmental Protection Agency (USEPA) has established threshold limits on some DBPs, which are known as regulated DBPs (R-DBPs). The human health risks associated with R-DBPs in drinking water distribution systems (DWDSs) and application of stricter regulations have led water utilities to switch from conventional disinfectant (i.e., chlorination) to alternative disinfectants. However, the use of alternative disinfectants causes formation of a new suit of DBPs known as unregulated DBPs (UR-DBPs), which in many cases can be more toxic. There is a growing concern of UR-DBPs formation in drinking water. This review prioritizes some commonly occurring UR-DBP groups and species in DWDSs based on their concentration level, reported frequency, and toxicity using an indexing method. There are nine UR-DBPs group and 36 species that have been identified based on recent published peer-reviewed articles. Haloacetonitriles (HANs) and haloacetaldehydes (HALs) are identified as important UR-DBP groups. Dichloroacetonitrile (DCAN) and trichloroacetaldehye (TCAL) are identified as critical UR-DBPs species. The outcomes of this review can help water regulators to identify the most critical UR-DBPs species in the context of drinking water safety and provide them with useful information to develop guidelines or threshold limits for UR-DBPs. The outcomes can also help water utilities in selecting water treatment processes for the mitigation of human health risk posed by UR-DBPs through drinking water.

Brewed tea a significant source of trihalomethane exposure

Fakour H, Lo SL. Formation and risk assessment of trihalomethanes through different tea brewing habits. Int J Hyg Environ Health. 2018 Sep 1. pii: S1438-4639(18)30193-7. doi: 10.1016/j.ijheh.2018.08.013.

Trihalomethanes (THMs) are suspected carcinogens and reproductive toxicants commonly found in chlorinated drinking water. This study investigates the formation of THMs and their associated risks during different tea brewing habits. Three main categories of tea (black, oolong, and green) under various brewing conditions and drinking water sources were tested. Tea samples prepared in ordinary thermos flask formed significant levels of total THM (TTHM). The highest TTHM formation came from black tea made with tap water, plausibly due to higher concentrations of reactive THM precursors. Compared with tap water, when the background solution is bottled water or distilled water, less TTHM was observed in prepared tea infusions. The results also revealed that unlike the traditional teapot-based tea serving habit, the removal of THMs is significantly reduced when tea infusion is stored in enclosed containers. Risk assessment analysis based on the survey among tea shop costumers also revealed that cancer risks induced by ingestion of THMs through drinking tea infusions prepared in thermos flask exceeded the tolerable level. Data obtained in this research demonstrated that drinking tea infusions directly from enclosed containers can be a significant source of exposure to THMs.

Total THM long-term exposure not related to female breast cancer, Spain

Font-Ribera L, Gràcia-Lavedan E, Aragonés N, Pérez-Gómez B, Pollán M, Amiano P, Jiménez-Zabala A, Castaño-Vinyals G, Roca-Barceló A, Ardanaz E, Burgui R, Molina AJ, Fernández-Villa T, Gómez-Acebo I, Dierssen-Sotos T, Moreno V, Fernandez-Tardon G, Peiró R, Kogevinas M, Villanueva CM. Long-term exposure to trihalomethanes in drinking water and breast cancer in the Spanish multicase-control study on cancer (MCC-SPAIN). Environment international. 2017 Dec 28;112:227-234. doi: 10.1016/j.envint.2017.12.031.

BACKGROUND: Exposure to trihalomethanes (THMs) in drinking water has consistently been associated with an increased risk of bladder cancer, but evidence on other cancers including the breast is very limited.

OBJECTIVES: We assessed long-term exposure to THMs to evaluate the association with female breast cancer (BC) risk.

METHODS: A multi case-control study was conducted in Spain from 2008 to 2013. We included 1003 incident BC cases (women 20-85 years old) recruited from 14 hospitals and 1458 population controls. Subjects were interviewed to ascertain residential histories and major recognized risk factors for BC. Mean residential levels of chloroform, brominated THMs (Br-THMs) and the sum of both as total THM (TTHMs) during the adult-lifetime were calculated.

RESULTS: Mean adult-lifetime residential levels ranged from 0.8 to 145.7μg/L for TTHM (median=30.8), from 0.2 to 62.4μg/L for chloroform (median=19.7) and from 0.3 to 126.0μg/L for Br-THMs (median=9.7). Adult-lifetime residential chloroform was associated with BC (adjusted OR=1.47; 95%CI=1.05, 2.06 for the highest (>24μg/L) vs. lowest (<8μg/L) quartile; p-trend=0.024). No association was detected for residential Br-THMs (OR=0.91; 95%CI=0.68, 1.23 for >31μg/L vs. <6μg/L) or TTHMs (OR=1.14; 95%CI=0.83, 1.57 for >48μg/L vs. <22μg/L).

CONCLUSIONS: At common levels in Europe, long-term residential total THMs were not related to female breast cancer. A moderate association with chloroform was suggested at the highest exposure category. This large epidemiological study with extensive exposure assessment overcomes several limitations of previous studies but further studies are needed to confirm these results.

THMs and HAAs in Small Water Systems, Canada

Chowdhury S. Occurrences and changes of disinfection by-products in small water supply systems. Environ Monit Assess. 2017 Dec 20;190(1):32. doi: 10.1007/s10661-017-6410-8.

The small water supply systems (WSSs) often report high concentrations of disinfection by-products (DBPs) in drinking water. In this study, occurrences of trihalomethanes (THMs) and haloacetic acids (HAAs) in Newfoundland and Labrador (NL), Canada, were investigated from 441 WSSs for a period of 18 years (1999-2016). The WSSs were divided into groundwater (GWP) and surface water (SWP) systems, which were further classified into eight sub-groups (P1-P8) based on the population served (≤ 100; 101-250; 251-500; 501-1000; 1001-3000; 3001-5000; 5001-10,000; and 10,000+, respectively). The DBPs with probable and possible carcinogenic forms were estimated. Overall, 31.1% of WSSs were GWP, in which averages of THMs and HAAs were 32.2 and 27.7 μg/L, respectively, while the SWP had averages of THMs and HAAs of 97.6 and 129.2 μg/L, respectively. The very small WSSs (P1-P3) of GWP had averages of THMs and HAAs in the ranges of 29.1-43.5 and 15.8-64.3 μg/L, respectively. The P1-P3 of SWP had averages of THMs and HAAs in the ranges of 92.6-112.8 and 108.0-154.0 μg/L, respectively, which often exceeded the Canadian guideline limits. If the samples represented the populations homogenously, the total populations exposed to THMs or HAA5 above the guideline values would be in the range of 132.08-181.38 in thousands (30.3-41.6% of total populations). The probable and possible carcinogenic forms of THMs in GWP and SWP were in the ranges of 4.8-48.8 and 4.4-7.0% of THMs, respectively. In HAAs, carcinogenic forms were in the ranges of 82.6-98.4 and 97.6-98.7%, respectively. The findings indicated that the SWP might need further attention to better protect human health.

Iodo-Trihalomethanes in Canadian Drinking Water

Tugulea AM, Aranda-Rodriguez R, Bérubé D, Giddings M, Lemieux F, Hnatiw J, Dabeka L, Breton F. The influence of precursors and treatment process on the formation of Iodo-THMs in Canadian drinking water. Water Res. 2017 Nov 27;130:215-223. doi: 10.1016/j.watres.2017.11.055.

The National Survey of Disinfection By-Products and Selected Emerging Contaminants investigated the formation of various disinfection by-products and contaminants in 65 water treatment systems (WTSs) across Canada. Results for six iodo-trihalomethanes (iodo-THMs) are reported in this paper. The participating water treatment systems included large, medium and small systems using water sources and treatment processes which were representative of Canadian drinking water. Five water samples (source water, treated water and three water samples along the distribution system) were collected from each treatment system, both under winter and summer conditions. Samples were stabilized, shipped cold and analysed for six iodo-THMs (dichloroiodomethane-DCIM; dibromoiodomethane-DBIM; bromochloroiodomethane-BCIM; chlorodiiodomethane-CDIM; bromodiiodomethane-BDIM and triiodomethane or iodoform-TIM), using a SPME-GC-ECD method developed in our laboratory (MDLs from 0.02 μg/L for iodoform to 0.06 μg/L for bromodiiodomethane). Concentrations of relevant precursors like dissolved organic carbon (DOC), bromide, iodide and total iodine, as well as other water quality parameters, were also determined. Detailed information about the treatment process used at each location was recorded using a questionnaire. The survey showed that one or more iodo-THMs were detected at 31 out of 64 water treatment systems (WTSs) under winter conditions and in 46 out of 64 WTSs under summer conditions (analytical results from one site were excluded due to sampling challenges). Total iodo-THM concentrations measured during this survey ranged from 0.02 μg/L to 21.66 μg/L. The highest total iodo-THM concentration was measured in WTS 63 where all six iodo-THMs were detected and iodoform was present in the highest concentration. The highest iodo-THM formation was found to occur in treatment systems where water sources had naturally occurring ammonium as well as high bromide, high iodide and/or total iodine concentrations. In two such water systems the total concentration of iodo-THMs exceeded the concentration of regulated THMs.

Validation Need for QSAR DBP Toxicity Models

Qin L, Zhang X, Chen Y, Mo L, Zeng H, Liang Y. Predictive QSAR Models for the Toxicity of Disinfection Byproducts. Molecules 2017 Oct 9;22(10). pii: E1671. doi: 10.3390/molecules22101671

Several hundred disinfection byproducts (DBPs) in drinking water have been identified, and are known to have potentially adverse health effects. There are toxicological data gaps for most DBPs, and the predictive method may provide an effective way to address this. The development of an in-silico model of toxicology endpoints of DBPs is rarely studied. The main aim of the present study is to develop predictive quantitative structure-activity relationship (QSAR) models for the reactive toxicities of 50 DBPs in the five bioassays of X-Microtox, GSH+, GSH-, DNA+ and DNA-. All-subset regression was used to select the optimal descriptors, and multiple linear-regression models were built. The developed QSAR models for five endpoints satisfied the internal and external validation criteria: coefficient of determination (R²) > 0.7, explained variance in leave-one-out prediction (Q²LOO) and in leave-many-out prediction (Q²LMO) > 0.6, variance explained in external prediction (Q²F1Q²F2, and Q²F3) > 0.7, and concordance correlation coefficient (CCC) > 0.85. The application domains and the meaning of the selective descriptors for the QSAR models were discussed. The obtained QSAR models can be used in predicting the toxicities of the 50 DBPs.

Acrylamide as a Disinfection Byproduct Precursor

Wang AQ, Lin YL, Xu B, Hu CY, Zhang MS, Xia SJ, Zhang TY, Chu WH, Gao NY. Degradation of acrylamide during chlorination as a precursor of haloacetonitriles and haloacetamides. The Science of the total environment. 2017 Sep 26;615:38-46. doi: 10.1016/j.scitotenv.2017.09.141.

Acrylamide is a monomer of polyacrylamide, which is widely used in the water treatment process as a flocculant. The degradation kinetics and formation of disinfection by-products (DBPs) during acrylamide chlorination were investigated in this study. The reaction between chlorine and acrylamide followed a pseudo-first-order kinetics. A kinetic model regarding acrylamide chlorination was established and the rate constants of each predominant elementary reaction (i.e., the base-catalyzed reaction of acrylamide with ClOas well as the reactions of acrylamide with HOCl and ClO) were calculated as 7.89×107M-2h-1, 7.72×101M-1h-1, and 1.65×103M-1h-1, respectively. The presence of Br in water led to the formation of HOBr and accelerated the rate of acrylamide degradation by chlorine. The reaction rate constant of acrylamide with HOBr was calculated as 1.33×103M-1h-1. The degradation pathways of acrylamide chlorination were proposed according to the intermediates identified using ultra-performance liquid chromatography and electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Five chlorinated DBPs including chloroform (CF), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), dichloroacetamide (DCAcAm), and trichloroacetamide (TCAcAm) were identified during acrylamide chlorination. The formation of CF, DCAN, DCAcAm, and TCAcAm kept increasing, while that of TCAN increased and then decreased with increasing reaction time. As the chlorine dosage increased from 0.75 to 4.5mM, DCAN became the dominant DBP. Large amounts of CF, DCAN, and TCAN were formed at basic pHs. The hydrolysis of DCAN and TCAN led to the formation of DCAcAm and TCAcAm, respectively. The results of this study elucidated that acrylamide can be a precursor for the formation of haloacetonitriles (HANs) and haloacetamides (HAcAms) during drinking water treatment.