W7 PM Metals in the Environment: Regulatory and Risk Concerns
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 327-329

(SUN-1117-849576) Modeling the response of a variety of freshwater ecosystems across the United States to changes in atmospheric mercury deposition associated with the Clean Air Mercury Rule.

Sunderland, Elsie¹, Knightes, Christopher², Ambrose, Robert², Johnston, John², ¹ U.S. Environmental Protection Agency, National Exposure Research Laboratory, Washington, DC, USA² U.S. Environmental Protection Agency, National Exposure Research Laboratory, Athens, Georgia, USA

ABSTRACT- In the United States, approximately 6% of women of child-bearing age exceed EPA's safe reference dose for methylmercury (MeHg). A variety of regulatory actions have been taken to reduce exposure of the US population to MeHg. Here we present results from a variety of case studies developed for the Clean Air Mercury Rule using the SERAFM, WASP and BASS modeling frameworks to investigate the relationship between declines in emissions from a variety of human sources and MeHg in biota. To do this, we applied our dynamic, ecosystem scale water body, watershed, and bioaccumulation models to five freshwater systems spanning a range of types across the United States. Aquatic ecosystems respond to changes in mercury deposition in a highly variable manner as a function of differences in their chemical, biological and physical properties. When presenting the results of the response times of different ecosystems and the magnitude of changes in fish mercury concentrations, we discuss the key sources of uncertainty currently limiting our ability to develop an a priori predictive model. While important advances have been made in recent years to enhance scientific understanding of the behavior of mercury in the environment, our ability to effectively model the range in response times for different systems is constrained by our limited knowledge of how methylation and bioaccumulation occur in various ecosystems. EPA is currently engaged in a variety of projects to enhance our multi-media modeling capabilities. Our long-term goal is to develop robust predictive tools that mechanistically characterize the relationship between the declines in emissions and concentrations in fish and wildlife.

Key words: mercury, models, U.S. EPA, bioaccumulation