Risk Assessment of Radon in Drinking Water (1999)
Chapter: D Risks Associated with Disinfection By-products Formed by Water Chlorination Related to Trihalomethanes (THMs)
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
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.
Summary Table of Risk Estimates for THMs in Surface Water
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|
|
Compound |
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|
|
|
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). |
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Summary Table of Risk Estimates for THMs in Ground Water
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|
|
Compound |
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|
|
|
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). |
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