Current risk assessment procedures are typically based on overall daily exposure levels, and tend to emphasize effects resulting from continuous exposure over a lifetime. However, scientists now realize that exposures are more likely to be experienced as bursts or spikes, or intermittent exposures of varying levels. The U.S. Environmental Protection Agency's Risk Assessment Forum is beginning to examine how dose-duration relationships are or can be incorporated into the risk assessment process for less-than-lifetime exposures. As part of this effort, the Forum, together with the Harvard School of Public Health, held a workshop August 5 and 6, 1998, to discuss the current understanding of dose-duration relationships, the approaches that can be used in their modeling, the inclusion of these relationships in risk assessment, and future directions in this area. The workshop provided a forum for open discussion and identifying areas of consensus, as well as areas of difference. This report contains an issue paper that was prepared to help identify improvements for the current risk assessment approach and gaps in knowledge and methodology, the workshop presentations, summaries of the issues discussed by the workshop breakout groups, and possible future directions for this scientific discipline.
U.S. EPA. Summary of the U.S. EPA Workshop on the Relationship Between Exposure Duration and Toxicity. U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Washington Office, Washington, DC, EPA/600/R-99/081, 1999.