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NEUROTOXICITY STUDIES OF SELECTED DISINFECTION BYPRODUCTS (DBPS)
Impact/Purpose:
The Stage 1 DBP rule proposed an MCLG for dichloroacetic acid (DCA) and an MCL for haloacetic acids (five) (HAA5). The results of these studies could increase our understanding of the toxicity of several disinfection byproducts (DBPs) and lead to a more accurate estimation of the risk, if any, to humans exposed to DBPs in finished drinking water for the Stage 2 DBP rule.
Description:
The neurotoxicity of DBPs in general has not been well characterized. The purpose of these studies is to develop hazard identification and dose response data on the neurotoxicity of selected DBPs. A neurotoxicological screening program involving a collaboration between the EPA and the National Toxicology Program (NTP) was initiated in FY99. Previous research at EPA was focused on dichloroacetic acid (DCA), and neuropathological assessments of DCA-treated rats are being finalized. Current studies will examine potential neurotoxicity of other DBPs. The first studies to be conducted include assessment of chlorate, dibromoacetic acid (DBA), and chlorodibromomethane. These studies will involve neurobehavioral testing of the rats at specified time intervals during 6-month exposure studies, followed by neuropathological evaluations. All compounds will be delivered in drinking water. Studies completed at EPA have shown that relatively low doses of DCA (as low as 16 mg/kg/day; similar to the lowest doses at which other noncancer effects have been observed experimentally) can cause neurotoxicity after several months of exposure. The effects are reversible at low-dose, short-term exposures, but are irreversible following high-dose exposures. Our studies have also shown that subchronic exposure to dibromoacetic acid (DBA), the brominated analog of DCA, produces neuromuscular toxicity as well as neuropathological changes in the spinal cord. DBPs of other chemical classes do not produce neurobehavioral changes; however, the pathological evaluations for those chemicals have not yet been finalized. These findings suggest that additional research to characterize the potential neurotoxicity of haloacids is warranted and will provide additional information for the estimation of risk in humans.