Exposure is critical in understanding the likelihood for adverse health effects to wildlife populations from environmental contamination. Wildlife experience the environment relative to species-specific life history constraints (e.g., habitat) which may overlap with variation in environmental contamination. Consideration of space in an environmental context is crucial, where significant resources are devoted to defining the nature and extent of contamination. Models contribute to environmental assessments from early site analyses through remedial planning, implementation, and monitoring. Accounting for spatially explicit relationships is an integral component in many of the most frequently applied fate and transport models, e.g., WASP (Gonenc et al. 2007), WASTOX (Connolly and Winfield 1994), and BASINS (Chigbu et al. 2007). Despite broad acceptance of fate and transport models that include spatial components, ecological risk assessments rarely consider the influences of habitat and contamination in a quantitative spatial context meaningful to an assemblage of individuals (populations).
Models provide scientists with the opportunity to increase the value of data collected at a particular contaminated site by facilitating additional research into alternative scenarios, leveraging data collected for predictions in areas lacking data and, when combined with non site-specific data, increasing the efficiency of future direct sampling by highlighting data gaps and clarifying data needs. Ecologists are challenged to incorporate increasingly realistic wildlife exposure scenarios in their work. Models that incorporate species- and site-specific data, and, where spatial interactions between environmental contamination and habitat preferences are made transparent and accessible, provide increased realism and enhance predictive capabilities. Recognition of the importance of spatial relationships in environmental assessments is not new. Early ecological risk assessment guidance documents discuss the importance of considering spatial characteristics in an assessment (USEPA 1997, 1998). In this context, these models are of value to risk assessors, environmental managers, and decision makers because of their ability to incorporate important spatial considerations related to exposure into risk characterization, and also to identify uncertainties associated with risk estimates. The challenge is to reach consensus among model developers, risk assessors, and regulators (and within each group, as well as among individuals who work in all three areas) regarding appropriate applications for new models. In addition, if consensus can be reached regarding the use of a spatially explicit model, then a project team must identify the appropriate model, model inputs and assumptions, and have a clear understanding about how the results may be interpreted before results are generated.
As part of an Environmental Security Technology Certification Program (ESTCP) project focusing on spatially explicit wildlife exposure model demonstration and testing, a workshop of U.S. Army, U.S. Environmental Protection Agency (USEPA), state regulators, and private sector researchers was convened to evaluate current applications of available spatially explicit wildlife exposure models and approaches for increasing future use of such models. The workshop focused on collecting insights with respect to 4 key questions: 1) What are spatially explicit wildlife exposure models and why are they valuable? 2) How have such models been applied? 3) Are there regulatory impediments to their use? and 4) What are the limitations of these models and how could they be improved? On the basis of detailed discussions during the 2-day workshop, a set of recommendations was developed using these important tools to estimate wildlife exposures. Although there are numerous applications (e.g., natural resource damage assessment, land-use planning) for these models, here, we concentrated on their applications within the ecological risk assessment (ERA) process—from initial screening assessment through remediation—with respect to contaminated sites. The following summary of our discussions during the workshop is intended to encourage ecological risk assessors to make greater use of spatially explicit exposure models and to provide recommendations for increasing the acceptance and use of such models in ecological risk assessments.