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Water: Drinking Water

Drinking Water Health Advisories - Criteria: Brominated Trihalomethanes

Brominated trihalomethanes are volatile organic liquids that have a number of industrial and chemical uses. The process of disinfecting drinking water generates brominated trihalomethanes as a by-product. The brominated trihalomethanes occurring in water are bromoform, dibromochloromethane, and bromodichloromethane. These compounds are formed when hypochlorous acid oxidizes bromide ion present in water to form hypobromous acid, which subsequently reacts with organic material to form the brominated trihalomethanes.

The Safe Drinking Water Act requires EPA to publish Maximum Contaminant Level Goals (MCLGs) and promulgate National Primary Drinking Water Regulations for each contaminant, which, in the judgment of the Administrator, may have an adverse effect on public health and which is known or anticipated to occur in public water systems. The MCLG is nonenforceable and is set at a level at which no known or anticipated adverse health effects in humans occur and which allows for an adequate margin of safety. Factors considered in setting the MCLG include health effects data and sources of exposure other than drinking water.

This document provides the health effects basis to be considered in establishing the MCLGs for brominated trihalomethanes found in chlorinated drinking water. To achieve this objective, data on pharmacokinetics, human exposure, acute and chronic toxicity to animals and humans, epidemiology and mechanisms of toxicity were evaluated. Specific emphasis is placed on literature data providing dose-response information. Thus, while the literature search and evaluation performed in support of this document was comprehensive, only the reports considered most pertinent in the derivation of the MCLGs are cited in this document. The comprehensive literature search in support of this document includes information published up to January, 2005; however, more recent information may have been added during the review process.

When adequate health effects data exist, health advisory values for less than lifetime exposure (One-day, Ten-day and Longer-term, approximately 10% of an individual's lifetime) are included in this document. These values are not used in setting the MCLGs, but serve as informal guidance to municipalities and other organizations when emergency spills or contamination situations occur.

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