D Risks Associated with Disinfection By-products Formed by Water Chlorination Related to Trihalomethanes (THMs)

1) Ingestion of Household Water with THMs General Assumptions

Drinking-water intake: 0.6 L d-1

Body weight: 70 kg

Person drinks water at home 7 d wk-1, 52 wk y-1

Exposure duration: 70 y

Averaging time for carcinogenic effects: 70 y (25,550 d)

Unit Dose Factor for Cancer Risk (lifetime average):

2) Inhalation Intake from Household Water with THMs Assumptions

Inhalation rate of moderately active people: 0.77 m3 h-1

Duration of time in house during a day: 17 h



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OCR for page 254
--> D Risks Associated with Disinfection By-products Formed by Water Chlorination Related to Trihalomethanes (THMs) 1) Ingestion of Household Water with THMs General Assumptions Drinking-water intake: 0.6 L d-1 Body weight: 70 kg Person drinks water at home 7 d wk-1, 52 wk y-1 Exposure duration: 70 y Averaging time for carcinogenic effects: 70 y (25,550 d) Unit Dose Factor for Cancer Risk (lifetime average): 2) Inhalation Intake from Household Water with THMs Assumptions Inhalation rate of moderately active people: 0.77 m3 h-1 Duration of time in house during a day: 17 h

OCR for page 254
--> Exposure duration: 70 y Averaging time for carcinogenic effects: 70 y (25,550 d) Average transfer coefficient = 0.1 µg / m3 (air)/µg/L (water) Unit Dose Factor for Cancer Risk (lifetime average): 3) Dermal Uptake from Bathing at Home Assumptions Body weight: 70 kg Area of body exposed during bathing: about 20,000 cm2 (in the range of central to upper estimate from EPA guidance) Effective permeability of THMs through skin for a 10-min exposure: 0.05 cm h-1, based on value for chloroform estimated by McKone (1993) from EPA and other models Bath or shower for 0.17 h (10 min) once per day, 365/day Exposure duration: 70 y Averaging time for carcinogenic effects: 70 y (25,550 d) Unit Dose Factor for Cancer Risk (lifetime average) = In the tables below, Risk = Cw x UDF x Potency. The total risk for each chemical is the sum of the risks across the three exposure routes.

OCR for page 254
--> Summary Table of Risk Estimates for THMs in Surface Water     Compound     Chloroform Bromodichloromethane Chlorodibromomethane Bromoform Total Risk Water Concentrationa µg L-1   90 12 5 2.1     Unit Dose Factor Potencies by Route       Ingestion 0.0086 0.031 0.13 0.094 0.008   Inhalation 0.019 0.019 0.13 0.094 0.004   Dermal uptake 0.0024 0.019 0.13 0.094 0.004   Total risk by chemical   6.1 × 10-5 4.7 × 10-5 1.4 × 10-5 3.2 × 10-7 1.2 × 10-4 a Data from Brass and others (1981). Summary Table of Risk Estimates for THMs in Ground Water     Compound     Chloroform Bromodichloromethane Chlorodibromomethane Bromoform Total Risk Water Concentrationa µg L-1   8.9 5.8 6.6 11     Unit Dose Factor Potencies by Route       Ingestion 0.0086 0.031 0.13 0.094 0.008   Inhalation 0.019 0.019 0.13 0.094 0.004   Dermal uptake 0.0024 0.019 0.13 0.094 0.004   Total risk by chemical   6.0 × 10-6 2.3 × 10-5 1.9 × 10-5 1.7 × 10-6 4.9 × 10-5 a Data from Brass and others (1981).