US EPA

The EPA has released a final report that presents and applies a method to estimate distributions of internal concentrations of trihalomethanes (THMs) in humans resulting from a residential drinking water exposure. The report presents simulations of oral, dermal and inhalation exposures and demonstrates the feasibility of linking the US EPA’s information Collection Rule database with other databases on external exposure factors and physiologically based pharmacokinetic modeling to refine population-based estimates of exposure.

This final report, Exposures and Internal Doses of Trihalomethanes in Humans: Multi-Route Contributions from Drinking Water, presents the results of an analysis in which multiple data sets and physiologically based pharmacokinetic models were combined to estimate the oral, dermal and inhalation route-specific contributions to internal doses of THMs, which are drinking water disinfection byproducts. It was supported by a contract to Wilkes Technologies, Inc. (Bethesda, MD). Point estimates of THM concentrations were taken from the Agency’s Information Collection Rule database; additional databases on external exposure factors, e.g. water use, household behaviors, human activity patterns, house volume and ventilation provided distributions of exposure data. The results demonstrated that the inhalation exposure pathway represents a significant contribution to THM internal doses.

Topics covered include:

• Data Quality and Assumptions
• Modeling and Integration Framework: concentrations of THMs in drinking water, water use patterns, human in-home behavioral characteristics, room volumes and ventilation, physiologically based pharmacokinetic modeling.
• Required Data.
• Population distributions of internal doses in the adult male, adult female and 6 year old child resulting from household contact with drinking water.
• Contributions of oral, dermal and inhalation routes to attained internal concentrations of THMs.

Review Draft - by 2010, develop scientifically sound data and approaches to assess and manage risks to human health posed by exposure to specific regulated waterborne pathogens and chemicals, including those addressed by the Arsenic, M/DBP and Six-Year Review Rules.

This is the final document. Results will be published in the peer reviewed literature.

U.S. EPA. Exposures and Internal Doses of Trihalomethanes In Humans: Multi-Route Contributions From Drinking Water (Final). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/087, 2006.

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