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Abstract

Arsenic concentrations in sediments in a wetlands located downgradient from a landfill in northeastern Massachusetts were found to be over 1,000 mg/kg in several locations with a maximum detected concentration of 4,500 mg/kg. The elevated arsenic in sediment is likely the result of the dissolution of iron and arsenic in the underlying rock under reducing conditions mobilized with the groundwater and co-precipitating out into the sediments when groundwater reaches the oxidizing surface water, producing an iron and arsenic bearing floc. Approximately 15 acres of wetlands appear to be impacted from elevated arsenic concentrations. To assess the potential impacts to human health and to determine the extent of acreage requiring remedial action, a site-specific bioavailability factor was developed using an in vitro laboratory assessment. While in vivo (live animal) studies are considered to be the most accurate measures of bioavailability for assessing absorption of contaminants by humans, the in vivo studies are expensive and lengthy. The in vitro approach undertaken for this assessment simulates digestive activity in the stomach, including residence time, pH, temperature, agitation, and solid to liquid ratio. This in vitro laboratory approach coupled with an adjustment based on in vivo data, along with a mineralogical characterization of the impacted sediments, served to develop a site-specific bioavailability factor that resulted in more accurate human health risk characterization results.



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