Science, policy, and trends of metals risk assessment at EPA: How understanding metals bioavailability has changed metals risk assessment at US EPA

The US Environmental Protection Agency (EPA) and the Office of Water have made significant changes in the approaches taken to assessing metals in the aquatic environment. Over the last 20 years, the Office of Water has progressed through a variety of metals assessment tools from total recoverable metal to the biotic ligand model. These changes were initially driven by the recognition that the total metals criteria were out of date and that emerging science would make it possible to address bioavailability more thoroughly. More recent drivers are expectations that the agency ensure the criteria are protective of endangered species and that the agency can bring the best available science to conducting total maximum daily loads (TMDLs) for waters not meeting uses because of metal contamination. Changes have included: moving from total recoverable metals concentration to dissolved metals and the development of dissolved metal to total metal translator guidance, the development of water effect ratios (WERs) guidance, and most recently incorporation of the biotic ligand model (BLM) into criteria derivation for aquatic life protection (USEPA, 2007a. Aquatic Life Ambient Freshwater Quality Criteria-Copper 2007 Revision. EPA-822-R-07-001. http://www.epa.gov/waterscience/criteria/copper/index.htm.). On March 8, 2007, the agency published its Framework for Metals Risk Assessment (USEPA, 2007b. Framework for Metals Risk Assessment. EPA 120/R-07/001. http://www.epa.gov/osa/metalsframework.) discussing the state of the science for the persistent bioaccumulative, and toxic nature of metals and the considerations of this science that will impact many programs. This paper provides a brief insight to these agency activities.