Table 5.
Benchmark doses and cancer risk concentrations for haloacetic acids and trihalomethanes.
| Disinfection Byproduct a | Benchmark Doses from Animal Bioassay, 5% Excess Cancer Risk (mg/kg-day) | Concentrations Corresponding to One-in-a-Million Cancer Risk c (µg/L) | Source of the Risk Benchmark |
|---|---|---|---|
| Bromochloroacetic acid | 1.0 (0.7–1.6) b | 0.02 | Calculated in this study |
| Chlorodibromoacetic acid | Not Available | 0.02 | Applied by read-across from bromochloroacetic acid |
| Bromodichloroacetic acid | 2.8 (1.6–9.1) b | 0.04 | Calculated in this study |
| Dibromoacetic acid | 2.2 (1.4–3.8) b | 0.04 | Calculated in this study |
| Tribromoacetic acid | Not Available | 0.04 | Applied by read-across from dibromoacetic acid |
| Trichloroacetic acid | 8.1 (4.4–28.8) | 0.1 | OEHHA 2020 [30] |
| Dichloroacetic acid | 32.7 (7.9–40.2) | 0.2 | OEHHA 2020 [30] |
| HAA5 group | Not applicable | 0.1 | Calculated in this study |
| HAA6Br group | Not applicable | 0.03 | Calculated in this study |
| HAA9 group | Not applicable | 0.06 | Calculated in this study |
| Bromodichloromethane | 11.1 (3.9–21.9) | 0.06 | OEHHA 2018 [42] |
| Dibromochloromethane | 26.2 (7.5–39.1) | 0.1 | OEHHA 2018 [42] |
| Chloroform | 33.4 (14.1–51.6) d | 0.4 e | OEHHA 2018 [42] |
| Bromoform | 31.0 (18.7–82.7) | 0.5 | [42] |
| THM4 group | Not applicable | 0.15 | Evans et al. [16] |
a There is no evidence of carcinogenicity for monobromoacetic acid and monochloroacetic acid. b Benchmark doses were modeled using 5% extra risk of tumor incidence in the liver of mice, the most sensitive site in exposed laboratory animals. c Risk-specific concentrations were calculated based on 95th percentile drinking water intake and adjustment factors to account for early-life sensitivity. d Benchmark modeling results for chloroform vary depending on the specific bioassay [42,56]; benchmark dose data reported here are from California OEHHA modeling of the data from the National Cancer Institute 1976 report on chloroform carcinogenicity [56]. e The benchmark, as reported by California OEHHA, is based on the geometric mean of cancer slope factors from five different animal studies [42].