US EPA: Mercury Study Report to Congress - Vol. 6 - An Ecological Assessment for Anthropogenic Mercury Emissions in the United States
Section 112(n)(1)(B) of the Clean Air Act (CAA), as amended in 1990, directs the U.S. Environmental Protection Agency (U.S. EPA) to submit to Congress a comprehensive study on emissions of mercury to the air. Volume VI, which addresses the ecological exposure and effects assessment for mercury and mercury compounds, is part of an eight-volume report developed by U.S. EPA in response to this directive. Volume VI is an ecological risk assessment for anthropogenic mercury emissions. It follows the format of the U.S. EPA Framework for Ecological Risk Assessment (U.S. EPA, 1992a), with minor changes as suggested in the draft Proposed Guidelines for Ecological Risk Assessment (U.S. EPA, 1996). The first step in the Framework is the problem formulation phase, wherein the potential ecological impacts of mercury are reviewed. This is followed by the presentation of a conceptual model describing how airborne mercury accumulates in aquatic biota, biomagnifies in aquatic food chains and is consumed by wildlife that eat contaminated fish. Subsequent steps in the assessment include exposure and effects assessments. Exposure and effects information are then considered together in an effort to develop qualitative statements about the risk of airborne mercury emissions to piscivorous avian and mammalian wildlife. An outcome of this effort is a recalculation of the wildlife criterion (WC) value for mercury in aquatic systems. A characterization of the risks to wildlife from anthropogenic mercury emissions is provided in Volume VII of this Report to Congress.