An approach to predict risks to wildlife populations from mercury and other stressors.

Ecological risk assessments for mercury (Hg) require measured and modeled information on exposure and effects. While most of this special issue focuses on the former, i.e., distribution and fate of Hg within aquatic food webs, this paper describes an approach to predict the effects of dietary methylmercury (CH3Hg) on populations of piscivorous birds. To demonstrate this approach, the U.S. Environmental Protection Agency's National Health and Environmental Effects Research Laboratory (U.S. EPA NHEERL) is working cooperatively with environmental and conservation organizations to develop models to predict CH3Hg effects on populations of the common loon, Gavia immer. Specifically, a biologically-based toxicokinetic model is being used to extrapolate CH3Hg effects on the reproduction of a tested bird species, the American kestrel (Falco sparverius), to the loon. Population models are being used to incorporate stressor effects on survival and reproduction into projections of loon population effects. Finally, habitat and spatially-explicit population models are being used to project results spatially, assess the relative importance of CH3Hg and non-chemical stressors, and produce testable predictions of the effects of biologically-available Hg on loon populations. This stepwise process provides an integrated approach to estimate the impact on wildlife populations of regulations that limit atmospherically-distributed Hg, and to develop risk-based population-level regulatory criteria.