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Drinking Water Disinfection By-Products: When, What and Why?

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Drinking Water Disinfection By-Products: When, What and Why? Drinking Water Disinfection By-Products: When, What and Why? Steve E. Hrudey, PhD, PEng Professor of Environmental Health Sciences A/Chair, Department of Public Health Sciences University of Alberta Overview z Brief History of Disinfection By-Products (DBPs) and Drinking Water z Classes of currently known DBPs z Physical and chemical properties of DBPs z Formation of DBPs in water treatment z Recent and emerging DBPs z Historical perspective: the chloroform story Brief History z Trihalomethanes (THMs), primarily chloroform, were first reported in drinking water by J. Rook (1974) in Holland, soon followed by Bellar et al. (1974). z THMs shown to be produced by chlorination reactions with natural organic matter in water (humic, fulvic acids) z THMs had been missed by earlier analytical schemes which used solvents of similar volatility to and including chloroform for extracting organics Brief History z Discovery of trace organics in drinking water was a major revelation to an industry which had come to believe that conventional water treatment “proven” for decades was all that was needed for “safe” drinking water. z Pattern of identifying contaminants by analytical advances, then looking for health effects was established (e.g. the drunk searching for lost keys under the light post approach to public health) z Pattern repeated in succeeding decades (Historical perspective) Classes of currently known DBPs z DBPs are by definition, the result of a reaction between a disinfecting agent (chemical or physical) and a precursor chemical in the source water z Therefore, DBP formation will depend on: disinfectant used precursors present reaction conditions provided Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Trihalomethanes Chloroform CHCl3 Bromodichloromethane CHCl2Br Dibromochloromethane CHClBr2 Bromoform CHBr3 Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Haloacetic acids Monochloroacetic acid CH2ClCOOH Dichloroacetic acid CHCl2COOH Trichloroacetic acid CCl3COOH Bromochloroacetic acid CHBrClCOOH Bromodichloroacetic acid CBrCl2COOH Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Haloacetic acids Dibromochloroacetic acid CBr2ClCOOH Monobromoacetic acid CH2BrCOOH Dibromoacetic acid CHBr2COOH Tribromoacetic acid CBr3COOH Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Haloacetonitriles Trichloroacetonitrile CCl3CN Dichloroacetonitrile CHCl2CN Bromochloroacetonitrile CHBrClCN Dibromoacetonitrile CHBr2CN Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Haloketones 1,1-Dichloroacetone CHCl2COCH3 1,1,1-Trichloroacetone CCl3COCH3 Miscellaneous Choral hydrate CCl3CH(OH)2 chlorinated organics Chloropicrin CCl3NO2 Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Cyanogen halides Cyanogen chloride ClCN Cyanogen bromide BrCN - Oxyhalides Chlorite ClO2 - Chlorate ClO3 - Bromate BrO3 Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Aldehydes Formaldehyde1 HCHO 2 Acetaldehyde CH3CHO Glyoxal OHCCHO Methyl glyoxal CH3COCHO 1formed from glycine 2formed from alanine Classes of currently known DBPs (after Froese et al. 1999) DBP Class Individual DBPs Chemical Formula 3 Aldehydes Isobutyraldehyde (CH3)2CHCHO 4 odorous Isovaleraldehyde (CH3)2CHCH2CHO 5 2-Methylbutyraldehyde (CH3)(C2H5)CHCHO 6 Phenylacetaldehyde (C6H5)CH2CHO 3formed from valine (Hrudey et al. 1988) 4formed from leucine (Hrudey et al. 1988) 5formed from isoleucine (Hrudey et al. 1988) 6formed from phenyalanine (Hrudey et al. 1988) Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Aldoketoacids Glyoxalic acid OHCCHO Pyruvic acid CH3COCOOH Ketomalonic acid HOOCCOCOOH Classes of currently known DBPs (adapted from Krasner 1999) DBP Class Individual DBPs Chemical Formula Carboxylic acids Formate HCOO- - Acetate CH3COO Oxalate OOCCOO -2 Maleic acids 2-tert-Butylmaleic acid HOOCC(C(CH3)3): CHCOOH Classes of currently known DBPs DBP Class Individual DBPs Chemical Formula Chlorophenols Chlorophenol C6H5Cl odorous Dichlorophenols C6H4Cl2 Trichlorophenols C6H3Cl3 1 Chloroanisoles Trichloroanisoles CH3OC6H3Cl3 odorous 1biotransformation of trichlorophenols Reported DBP Concentration Ranges (adapted from IPCS 2000) DBP Minimum (µg/L) Maximum (µg/L) Trihalomethanes 3.1 1280 Haloacetic acids <0.5 1230 Haloacetonitriles 0.04 12 Haloketones 0.9 25.3 Chlorophenols 0.5 1 Chloral hydrate 1.7 3.0 Chloropicrin <0.1 0.6 Disinfectants and DBPs (adapted from ICPS 2000) Disinfectant Significant Significant Significant non- organohalogen inorganic DBPs halogenated DBPs DBPs Chlorine THMs, HAAs, chlorate (mostly Aldehydes, HANs, CH, CP, from hypochlorite cyanoalkanoic acids, CPh, N-chloramines, use) alkanoic acids, halofuranones, benzene, carboxylic bromohydrins acids, Chlorine chlorite, chlorate unstudied dioxide Disinfectants and DBPs (adapted from ICPS 2000) Disinfectant organohalogen inorganic non-halogenated DBPs DBPs DBPs Chloramine HANs, cyanogen chloride, nitrate, nitrite, aldehydes, ketones, organic chloramines, CH, chlorate, hydrazine nitrosamines chloramino acids, haloketones Ozone bromoform, MBA, DBA, chlorate, iodate, Aldehydes, dibromoacetone, bromate, hydrogen ketoacids, ketones, cyanogen bromide peroxide, HOBr, carboxylic acids epoxides, ozonates DBP Concentrations for Chlorine (Krasner et al. 1989) or Ozone (Siddiqui et al. 1993) DBPs Median Concentration Median Concentration µg/L : chlorination µg/L : ozonation THMs 40 <1.0 chloroform 15 - BDCM 10 - DBCM 4.5 - bromoform 0.6 <1.0 DBP Concentrations for Chlorine (Krasner et al. 1989) or Ozone (Siddiqui et al. 1993) DBPs Median Concentration Median Concentration µg/L : chlorination µg/L : ozonation HAAs 20 <5.0 MCA 1.2 - DCA 6.8 - TCA 5.8 - MBA <0.5 <1.0 DBA 1.5 <5.0 DBP Concentrations for Chlorine (Krasner et al. 1989) or Ozone (Siddiqui et al. 1993) DBPs Median Concentration Median Concentration µg/L : chlorination µg/L : ozonation HANs 2.5 <1.0 TCAN <0.012 - DCAN 1.1 - BCAN 0.58 - DBAN 0.48 <1.0 DBP Concentrations for Chlorine (Krasner et al. 1989) or Ozone (Siddiqui et al. 1993) DBPs Median Concentration Median Concentration µg/L : chlorination µg/L : ozonation Aldehydes 7.8 45 formaldehyde 5.1 20 acetaldehyde 2.7 11 glyoxal - 9 methylglyoxal - 5 DBP Concentrations for Chlorine (Krasner et al. 1989) or Ozone (Siddiqui et al. 1993) DBPs Median Concentration Median Concentration µg/L : chlorination µg/L : ozonation Haloketones 0.94 - dichloropropanone 0.46 - trichloropropanone 0.35 - Chloral hydrate 3.0 - Keto acids - 75 Trichlorophenol <0.4 - Physical and Chemical Properties z basic properties (KH Kow) of individual compounds will determine several important factors: fate in treatment processes fate in distribution fate at end use human exposure routes z basic properties useful for assessing removal and human exposure z available data is poor Physical and Chemical Properties DBP Log Octanol - Water Henry’s Law Constant Trihalomethanes Partition Coefficient (Pa m3 mol-1) chloroform 1.97a 440a bromodichloromethane 1.41, 2.1a 160a chlorodibromomethane 2.24a 86a bromoform 2.30b, 2.38b 54b, 57b slightly lipophilic volatilization significant aHoward 1990 bMontgomery and Welkom 1990 Physical and Chemical Properties DBP Log Octanol - Water Henry’s Law Constant Haloacetonitriles Partition Coefficient (Pa m3 mol-1) dichloroacetonitrile -0.59c,1 0.36 est.3 trichloroacetonitrile 2.09d,2 0.14 est.3 Other chloral hydrate 1.46c,2 0.0006 est.4 3 1hydrophilic slight volatilization 4 2slightly lipophilic negligible volatilization cBodo et al. 2001 dHoward 1991 Physical and Chemical Properties z Haloacids have are very hydrophilic (water soluble) z Haloacids are non-volatile z Exposure to haloacids likely to be limited to ingestion uses of drinking water z Exposure to halomethanes has been shown to be strongly influenced by vapour-phase and dermal exposures (e.g. showering and bathing) z Suggests differing exposures for the same water supply will occur at individual level Physical and Chemical Properties DBP Log Octanol - Water Henry’s Law Constant various Partition Coefficient (Pa m3 mol-1) hexachloroacetone 2.48e,2 0.00088 e,4 2,4,6 trichlorophenol 3.69f,3 0.000000062 est.4 chloropicrin 2.09d,2 0.0021d 3 2slightly lipophilic very slight volatilization 3 lipophilic 4negligible volatilization dHoward 1991 eHoward 1997 fHoward 1989 Formation of DBPs in Treatment z since the discovery of DBPs in drinking water there has been a concerted research effort to understand how DBPs are formed and how they can be avoided z most research was initially directed at THMs and variations on chlorination z alternative disinfectants have been pursued, initially to avoid THMs and other halogenated DBPs z experience has shown DBPs are produced to some degree by most circumstances: can reduce but not eliminate Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Contact Curvilinear Curvilinear Linear Linear Curvilinear Time increase with increase with increase with increase in increase contact time contact time residual bleach Most bromate Rapid Rapid present No effect at in <5 min formation <5h formation <5h Secondary dilute conc. Formation a 90% in 24h 90% in 24h
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