ANALYSIS OF THE METHYLMERCURY FRACTION IN SURFACE WATER AND THE IMPACT ON MULTIPATHWAY RISK ASSESSMENT FOR HWCS

摘要

Mercury is one of the key chemicals that drive the results of multipathway risk assessments (MPRA) for waste combustion facilities. The dominant exposure pathway is human consumption of fish caught in freshwater bodies within the impact area. The U.S. Environmental Protection Agency (EPA) has developed a series of fate and transport models to estimate the methylmercury concentration in fish, which have been widely applied in MPRAs. One of the key parameters used in these models is the assumed fraction of methylation of mercury that occurs under various loading mechanisms to local freshwater bodies. This paper presents a comparative analysis of the application of the methylmercury fraction in the fate and transport modeling of an MPRA performed for a hazardous waste combustion facility. The analysis reveals that there are inaccuracies in the application of the assumed methylmercury fraction within the EPA fate and transport modeling methodology for use in MPRAs that can lead to substantial overestimates of methylmercury in the water column and in fish, which would subsequently overestimate the associated risks to human health. This paper also discusses adjustments to the EPA methodology to correct for estimating methymercury fractions in the total water body, water column, and bed sediment.