Toxicology of Chlorinated Disinfection By-products

Barry H. Thomas, Ph.D

Consulting Toxicologist in Environmental HealthP.O. Box 41, 120 Jennings Settlement Road

Tangier, NS B0J 3H0

Introduction

Personal

Disinfection of Drinking WaterChlorineChloramineOzoneUltraviolet Light

Disinfection DilemmaRaising chlorine concentrations produces higher levels of chlorination by-productsRemoving natural organic matter before chlorination reduces by-product levelsThe high cost of organic removal is a serious economic/political problemChlorine concentration must always be maintained at an adequate level for disinfection until the by-product problem can be solved

Exposure and ToxicityHealth Risk = Exposure x ToxicityExposure = Water consumed x ConcentrationToxicity = Maximum dose that is safe expressed as ug per kg body weight per dayVOCs: Ingestion, Inhalation and Dermal absorption

Factors affecting CDBP levelsChlorine concentrationContact timeLevel of natural organic matterpHBromideTemperature

Commonly found CDBPs - 1Trihalomethanes, CH.X3

Chloroform, CH.Cl3Bromodichloromethane, CH.Cl2BrDibromochloromethane, CH.ClBr2

Bromoform, CH.Br3

Commonly found CDBPs - 2Haloacetic acids, HAAsMonochloroacetic acid, MCA, Cl.CH2.COOHDichloroacetic acid, DCA, Cl2.CH.COOHTrichloroacetic acid, TCA, Cl3.C.COOHBrominated acetic acids (6 identified)

Other minor CDBPsChloral Hydrate, CH, 6.1 ug/LHaloacetonitriles, HANs, e.g. Dichloroacetonitrile, 2.9 ug/L1,1,1-Trichloropropanone, 2.7 ug/L

Typical CDBP concentrations

0

10

20

30

40

50

60

70

THMs DCA TCA CH

Concentration, µg/L

National Survey of Chlorination Disinfection By-Products in Canadian Drinking Water, Health Canada 1995.www.hc-sc.gc.ca/hecs-sesc/water/pdf/eng_pt1.pdf

Toxicity review – Animal studiesControlled environmentAccurate dosesEthicsSpecies differences

Toxicity review- Human epidemiological studies

No species differencesComplex, highly variable environment/life-styleDose uncertainEthical limitations

Epidemiological studies - EcologicalCompare disease rates in different geographic areasMany possible causes of different disease ratesNever conclusive, might give cluesInexpensive

Epidemiological studies – Case controlDose can be more accurately estimatedConfounders can be controlled if knownVery expensive – can be $millionsStill not conclusive

Critical health effectsLiterature review of all toxic endpointse.g. neurotoxicity, cancer, reproductive, immunological, etc.Endpoint that is shown at the lowest exposure level is chosen for quantitative risk assessment

Trihalomethanes (THMs)Chloroform

Chloroform causes kidney and liver tumours in rodents BUT now believed NOT to be due to an affect on DNANo evidence of human cancer despite extensive occupational exposureThe tolerable daily intake (TDI) of 6.2 ugper kg body weight per day is derived from liver toxicity in a dog studyTHMs levels above 50 ug/L have been associated with bladder and colon cancer

Bromodichloromethane (BDCM)Major brominated THMRodent tumours in the intestine, kidney and liverProbably genotoxic (i.e. changes DNA)Calculated cancer risk at a level of 16 ug/L is 10-5 (1 cancer per 100,000 people drinking the water for a lifetime of 70 yrs)Association between BDCM levels and stillbirth, retarded fetal growth and spontaneous abortion

Chlorinated haloacetic acids (HAAs)Not in current Canadian guidelines but coming soonDifficult to measureUS EPA has regulated HAAs for many yearsRegulations based solely on animal studies since no human data available

Monochloroacetic acid (MCA)No evidence of carcinogenicityNo evidence of genotoxicitySignificant changes in body and organ weights in ratsTDI of 3.9 ug per kg body weight per day

Dichloroacetic acid (DCA)Liver tumours in rats and miceProbable human carcinogenA level that gives a 10-5 cancer risk after a lifetime of exposure is achievable

Trichloroacetic acid (TCA)Liver tumours in micePeroxisome proliferation casts doubt on relevance of mouse resultPossible human carcinogenTDI of 32.5 ug per kg body weight per day based on liver toxicity in rats

Chloral hydrate (CH)Pituitary tumours in female mice were the only significant cancer effectUsed as drug for a long time without any apparent cancer effectPossible human carcinogenTDI of 4.5 ug per kg body weight per day based on the incidence of proliferativelesions in the liver of male mice

Regulated levels - 1THMs, IMAC 0.1 mg/L (proposed MAC 0.1 mg/L based on an annual average of a minimum of quarterly samples taken at the extremities of the distribution system)BDCM, No current guideline (proposed MAC 0.016 mg/L based on an annual average of a minimum of quarterly samples taken at the extremities of the distribution system)

Regulated levels- 2HAAs No Canadian guidelines although a proposal from Health Canada is being prepared

HAA5 (US EPA), MCL 0.06 mg/L (MCA, DCA, TCA, Bromoacetic acid and Dibromoacetic acid)

Chloral hydrate (CH)No current guidelineRisk assessment gave a proposed MAC of 200 ug/L – well above levels seen in drinking waterNo guideline recommended

ConclusionCDBPs are a significant health riskTechnological solutions are usually possibleNeed to balance the drinking water risks against other public health issues that require fundingAdequate disinfection is the number one priorityHealth Canada Drinking Water Web Page www.hc-sc.gc.ca/hecs-sesc/water/index.htm