Development and test application of a screening-level mercury fate model and tool for evaluating wildlife exposure risk for surface waters with mercury-contaminated sediments (SERAFM)

Complex chemical cycling of mercury in aquatic ecosystems means that tracing the linkage between anthropogenic and natural loadings of mercury to watersheds and water bodies and associated concentrations in the environment are difficult to establish without the assistance of numerical models that describe biogeochemical controls on mercury distribution and availability to organisms. This paper presents an overview of a process-based, steady-state model developed for state and water quality managers and scientists to assist in ecological risk assessments for mercury in aquatic environments. SERAFM (Spreadsheet-based Ecological Risk Assessment for the Fate of Mercury) incorporates the chemical, physical, and biological processes governing mercury transport and fate in a surface water including atmospheric deposition, watershed transport and transformation, solid transport and cycling within the water body, and water body mercury processes. This modelling framework was designed to assist risk assessors in evaluating wildlife risk at the screening-level for an aquatic ecosystem with mercury-contaminated sediments. An example application of the model that is used to inform a regional risk assessment is presented in this manuscript. In the example provided, hazard quotients for exposed wildlife and humans are calculated by the model for three scenarios: historical case of mercury-contaminated sediments, required clean-up levels to protect the most sensitive species, and background conditions. The spreadsheet structure of SERAFM permits dismantling and reassembling of specific sub-modules, while maintaining transparency to permit flexibility in use and application.