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 reactions If oxidation of function of Levels off levels off between hypochlorite, ozone residual disinfectants at 96h at 150h contact time and bromide & aldehydes has positive possible effect Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Disinfectant Rapid and Curvilinear Curvilinear for Concentration Linear Dose curvilinear increase after increasing related to increase after increase after TOC demand ozone or hypochlorite TOC demand TOC demand with chlorine dose doses applied and then with dose, increasing No effect after Ozone leveling off leveling off at dose, leveling ozone / DOC oxidation of after ozone TOC of 2 off at 2 mg/L = 2:1 hypochlorite residual mg/L increases with disappearance dose Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite pH Curvilinear Mixed, Negative Positive effect Strong linear increase with possible pH effect (forms Decompose positive effect increasing pH max for mostly hypochlorite Hydroxyl to pH 7.0 and DCAA and through increasing radical possible pH DBAA molecular with pH generation max. TCAA ozone) Oxidation of efficiency No positive decreases up 25% decrease hypochlorite increases effect at pH to pH >9 for pH 7 - 8.5 by ozone >9.5 DCAA max at increases pH 7 - 7.5 Impact of Water Quality and Treatment Variables on DBP Formation (Krasner 1999) DBP pH 5 pH 7 pH 9.4 THMs Lower formation Higher formation TCAA Similar formation Lower formation DCAA Similar Perhaps slightly higher Formation Chloral hydrate Similar formation Forms within 4 h Decays over time DCAN Higher formation Forms within 4 h Lower formation Decays over time Trichloroacetone Higher formation Lower formation Not detected Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Temperature Linear Linear Terminal Positive effect Curvilinear increase with increase with products such Decompose of increase 20 to increasing increasing as carbon hypochlorite 30% increase temperature temperature dioxide increases for 15 to 25 C (10 to 30 C; (10 to 30 C; increase and 15 to 25% 15 to 25% total increase) increase) aldehydes slightly decrease Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite TOC Increase with Increase with Positive effect Negative Decrease with increasing increasing (hydrophobic effect if ozone increasing TOC; TOC; fraction most is used for TOC; Precursor Precursor respsonsible) hypochlorite Precursor content content Doubles for oxidation content is important important every 2 mg/L Most likely no important Humic acids Humic acids effect with Non-humic more reactive more reactive hypochlorite acid less than fulvic than fulvic reactive with acids acids ozone Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Increase with Increase with Positive effect Negative Decrease with UV abs254 increasing UV increasing UV Ozone effect if ozone increasing UV absorbance; absorbance; demand is used for abs; Precursor Precursor increases with hypochlorite Precursor content content UV abs oxidation content is important; important; (UV abs is Probable important Aromaticity of Aromaticity of mostly due to negative Humic acid TOC being TOC being aromaticity & effect with more reactive more more hydrophobic hypochlorous with ozone important important fraction) acid Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Bromide Shift towards Shift towards Independent Shift towards Bromide brominated brominated of bromide at more toxic threshold species species <0.25 mg/l bromate in Curvilinear At >0.25 mg/L hypochlorite increase adehydes can solutions dependent decrease due upon ozone to ozone- residual bromide oxidation demand Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Minimization TOC removal, TOC removal, pH control Avoid pH depression, Strategies Alternative Alternative TOC removal hypochlorite Ammonia disinfectants disinfectants by coagulation dosing addition, pH control pH control GAC solution Radical Operatign Minimize scavengers Minimizing Minimizing doses Cl residual Cl residual storage Minimizing 2 2 Contact time Minimizing Minimizing Properly tune and Alternate generators optimizing contact time contact time disinfectants Use fresh ozone residual solutions Competing risks? Impact of Water Quality and Treatment Variables on DBP Formation (CCPS 2000) Variable THMs HAAs aldehydes chlorate / bromate chlorite Alkalinity No effect No effect Positive Unknown Positive discernable discernable effect, slight effect Removal GAC, GAC, Biofiltration, Ferrous Ferrous Strategies electron electron Advance sulfate, sulfate, UV, beam, air beam oxidation, GAC, electron stripping, GAC, electron beam, GAC, (effective?) nanofilters beam, UV, nanofilters Recent and Emerging DBPs z THMs and HAAs dominate the known DBPs z As more analytical power is trained on the search for DBPs, new compounds continue to be reported z New disinfectants like UV do produce DBPs, we just have not researched this adequately z Major gaps exist for more water soluble, non-volatile and thermally labile fractions Recent and Emerging DBPs z Mass balance on halogenated DBPs (based on TOX) suggest that less than half of total halogenated organics have been identified z No mass balance is possible to account for quantity of non- halogenated DBPs that remain unidentified. z New analytical approaches are necessary to assess the full spectrum of possible DBPs Recent and Emerging DBPs (after Arbuckle et al. In Press)

Halogenated furanones

3-Chloro-4-(bromochloromethyl)-5-hydroxy-2(5H)-furanone (BMX-l)

3-Chloro-4-(dibromomethyl)-5-hydroxy-2(5H)-furanone (BMX-2)

3-Bromo-4-(dibromomethyl)-5-hydroxy-2(5H)-furanone (BMX-l)

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) Recent and Emerging DBPs (after Arbuckle et al. In Press)

Haloacids Halonitromethanes z 3,3 Dichloropropenoic acid z Dibromonitromethane

Halomethanes Haloacetonitriles z Bromochloroiodomethane z Bromochloroacetonitrile z Dichloroiodomethane z Dibromoacetonitrile Recent and Emerging DBPs (after Arbuckle et al. In Press) Haloketones Haloamides z 1,1,3-Trichloropropanone z 2,2-Dichloroacetamide z 1,1-Dibromopropanone Aldehydes Haloaldehydes z 2-Hexenal z Dichloroacetaldehyde z Cyanoformaldehyde z Bromochloracetaldehyde Haloacetates Nitrosamines z Bromochloromethyl acetate z Nitrosodimethylamine (NDMA) Historical Perspective: The Chloroform Story z chloroform had been widely used in consumer products from cough syrup to toothpaste; also used as an anaesthetic z National Cancer Institute 1976 rodent cancer bioassay declared chloroform to be a carcinogen z Several epidemiologic studies over past 25 years have suggested an elevated cancer risk among consumers of “chlorinated water supplies” z A few recent epidemiologic studies suggest an association between THM exposures and adverse reproductive outcomes Historical Perspective: The Chloroform Story z Australia 250 µg/L TTHMs (max) set in 1996 z USA 100 µg/L TTHMs (annual avg) in 1979 changed to 80 µg/L TTHMs (annual avg) in 1998 z Canada: 350 µg/L TTHMs (max) set in 1978 changed to 100 µg/L TTHMs (annual avg) in 1996 (1993) z WHO 30 µg/L chloroform (annual avg) in 1984 changed to 200 µg/L chloroform (annual avg) in 1993 100 µg/L bromoform (annual avg) in 1993 100 µg/L dibromochloromethane (“”) in 1993 60 µg/L bromodichloromethane (“”) in 1993 Rationale for Numbers z Original rationale was based on cancer risk numbers calculated using cancer slope factors derived from rodent bioassays z Meaning of cancer slope factors based on linearized low dose models is now widely recognized as demanding close scrutiny z Meaning of slope factors is NIL for carcinogens acting by non-genotoxic mechanisms, i.e. chloroform Slope Factor Dependence on MTD *Risk = Slope x Dose*

RESPONSE constrained to 2 decades

DOSEs determined by MTDs Response which range over 9 decades Dose - POTENCY, response slope, q * anchored at 1 (0,0) Dose Rationale for Numbers z Australian DWG recognized non-genotoxic nature of chloroform and derived TTHM guideline based on a NOAEL divided by 100 fold safety factor z Last Canadian DWG of 1996 was based on rationale developed in 1993 assuming cancer slope factor approach yielding a lifetime cancer risk of 4 in a million. Risk by Non-Threshold (LMS) vs Threshold (NOAEL)(Butterworth et al. 1995) z Risk Specific Dose (RSD) at 10-5 lifetime cancer risk for chloroform using default LMS model is 60 ppb z NOAEL for B6C3F1 mice drinking water studies was 1,800,000 ppb, so for Uncertainty Factors (UF) of 100, Reference Dose (RfD) would be 18,000 ppb z NOAEL for Osborne-Mendel rat drinking water studies was 900,000 ppb, so for UF of 100, RfD would be 9,000 ppb z would need Uncertainty Factors of 15,000 to 30,000 to bring RfD down to RSD level from LMS Historical Perspective: The Chloroform Story z U.S. EPA policy for carcinogens in drinking water called for a maximum contaminant level goal (MCLG) of zero z Chloroform had been declared a carcinogen based on 1976 NTP rodent bioassay z THM MCL was originally driven by chloroform based on linear extrapolation of cancer risk with no threshold z This extrapolation approach is predicated on a carcinogen being directly DNA-reactive (e.g. genotoxic) Historical Perspective: The Chloroform Story z Mounting toxicological evidence indicated that chloroform exposure caused toxicity to cell tissues leading to regenerative cell proliferation z This mechanism can increase tumour risk, but is not a DNA- reactive mechanism and the no-threshold model is not appropriate z U.S. EPA expert review panel recommended abandoning the MCLG of zero with a limit based on estimated threshold Historical Perspective: The Chloroform Story (Pontius 2000) z The U.S. EPA proposed in 1998 to raise the MCLG to 0.3 mg/L based on the expert advice z Many intervenors protested this proposal as a precedent-setting measure (which it was) z U.S. EPA final rule withdrew the proposal to change the MCLG for chloroform from zero Historical Perspective: The Chloroform Story (Pontius 2000) z The Safe Drinking Water Act requires the U.S. EPA to use the best available science in setting standards z In opting for retaining the zero MCLG, the U.S. EPA acknowledged that the best available science called for raising the MCLG above zero z The Chlorine Chemistry Council sought a court review of the U.S. EPA decision Historical Perspective: The Chloroform Story (Pontius 2000) z On March 31, 2000 the U.S. District Court ruled that the U.S. EPA had violated the SDWA by failing to use the best available science z The court found the zero MCLG to be “arbitrary and capricous” and in excess of statutory authority z The perspective on DBP risks continues to evolve Are We Making Progress? A Chicken or Egg Dilemma z DBP monitoring data is based on what d.w. guidelines require to be monitored z d.w. guidelines, until now, have been based on animal toxicology risk assessments (mainly cancer) z retrospective epidemiology can only test causal hypotheses using available monitoring data for assessing exposure z question remains, exposure to what? z we can never know if the what actually causes disease in humans without meaningful epidemiologic data Conclusions z Countless DBPs have been identified and will continue to be identified z Complexity of DBP exposure is large

Volatile vs. non-volatile

High bromide vs. low bromide

Halogenated vs. non-halogenated z Risk assessment have been blind to majority of DBPs z DWG have been precautionary, given the evidence References Cited Arbuckle, T.E. et al. 2002. Assessing exposure in epidemiologic studies for disinfection by- products in drinking water: Report from an international workshop. Env. Health Persp. In press. Bellar, T.A. et al. 1974. The occurrence of organohalides in chlorinated drinking water. J.AWWA. 66(12: 703-706. Bodo, K. et al. 2001. Experimental determination of the N-octanol-water partition coefficient for dichloroacetonitrile (DCAN) and chloral hydrate (CH). Proc. 9th National Conf. on Drinking Water. Canadian Water and Wastewater Association. Ottawa. 301-308. Butterworth et al. In: Bull, R.J. et al. Water chlorination: essentail process or cancer hazard? Fundamental Appl. Toxicol. 28: 155-166. Froese et al. 1999. Factors governing odorous aldehyde formation as disinfection by-products in drinking water. Water Res. 33:1355-1364. Howard, P.H. 1989. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Vol. 1. Lewis Publ. Chelsea, Mich. Howard, P.H. 1990. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Vol. 2. Lewis Publ. Chelsea, Mich. Howard, P.H. 1991. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Vol. 3. Lewis Publ. Chelsea, Mich. References Cited Howard, P.H. 1997. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Vol. 5. Lewis Publ. CRC Press, Boca Raton, Florida. Hrudey, S.E. et al. 1988. Potent odour-causing chemicals arising from drinking water disinfection. Water Sci. Technol. 20(8/9) 55-61. ICPS. 2000. Disinfectants and Disinfectant By-products. Environmental Health Criteria 216. International Program on Chemical Safety. World Health Organization. Geneva. Krasner, S. 1999. Chemistry of Disinfection By-Product Formation. Chapter 2. In: Formation and Control of Disinfection By-Products in Drinking Water. Ed. P.C. Singer. American Water Works Association. Denver, CO. Krasner, S. et al. 1989. The occurrence of disinfection by-products in U.S. drinking water. J.AWWA. 81(8): 41-53. Montgomery, J.H. & L.H. Welkom 1990. Groundwater Chemicals Desk Reference. Lewis Publ. Chelsea, Mich. Pontius, F.W. 2000. Chloroform: science, policy and politics. J.AWWA. 92(5): 12, 14, 16, 18. Rook, J.J. 1974. Formation of haloforms during chlorination of natural water. Water Treat.Exam. 23:234-243. Siddiqui, M.S. & G.L.Amy. 1993. Factors affecting DBP formation during ozone-bromide reactions. J.AWWA. 85(1): 63-72.