ANALYSIS OF THE METHYLMERCURY FRACTION IN SURFACE WATERAND 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 consumptionof fish caught in freshwater bodies within the impact area. The U.S. Environmental ProtectionAgency (EPA) has developed a series of fate and transport models to estimate the methylmercuryconcentration in fish, which have been widely applied in MPRAs. One of the key parametersused in these models is the assumed fraction of methylation of mercury that occurs under variousloading mechanisms to local freshwater bodies. This paper presents a comparative analysis of theapplication of the methylmercury fraction in the fate and transport modeling of an MPRAperformed for a hazardous waste combustion facility. The analysis reveals that there areinaccuracies in the application of the assumed methylmercury fraction within the EPA fate andtransport modeling methodology for use in MPRAs that can lead to substantial overestimates ofmethylmercury in the water column and in fish, which would subsequently overestimate theassociated risks to human health. This paper also discusses adjustments to the EPA methodologyto correct for estimating methymercury fractions in the total water body, water column, and bedsediment.