A COMPARISON OF TWO MERCURY ENVIRONMENTAL FATE AND TRANSPORT MODELS IN EVALUATING INCINERATOR EMISSIONS

摘要

Human health and ecological risk assessments for waste incinerators often show that exposure to mercury from fish ingestion contributes significantly to the risk results. One of the most important elements in the analysis of mercury in incinerator risk assessments is the fate and transport modeling of mercury in waterbodies. The U.S. Environmental Protection Agency (USEPA) provides mercury modeling algorithms for waste incinerator risk assessments in its 1998 Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities (Risk Assessment Protocol). These algorithms, however, do not reflect the more refined USEPA mercury model referred to as IEM-2M, a model that has been applied by USEPA in the Mercury Report to Congress (MRTC) as well as the Utility Report to Congress. The IEM-2M model better addresses the complexities of the chemistry, environmental fate, and transport of combustion source mercury emissions in both watershed and waterbody environments. This paper describes the application of the IEM-2M model to a waste incinerator risk assessment. The IEM-2M model was used to calculate mercury concentrations in fish associated with mercury emissions from an incinerator’s stack. The IEM-2M model is described and input parameter requirements and model outputs are presented. A comparison of results for the two models shows that concentrations in water calculated using IEM-2M were four times lower for divalent mercury and more than 10 times lower for methyl mercury than those calculated using USEPA's Risk Assessment Protocol. The benthic sediment concentrations of divalent and methyl mercury were 1.5 times lower and 10 times higher, respectively, using IEM-2M compared to the Risk Assessment Protocol. The mercury fish tissue concentration, and associated fish ingestion risk, calculated according to the MRTC using IEM-2M model results was more than 100 times lower than that calculated using the methods presented in the Risk Assessment Protocol.