Dioxin Transport from Contaminated Sites to Exposure Locations: A Methodology for Calculating Conversion Factors

摘要

Procedures have been developed by the US EPA for estimating the risk associated with exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin). Concentrations of dioxin at the contaminant source are usually known, but exposure may occur at locations away from the source where concentrations are usually unknown. As a result, a need was identified for estimating dioxin concentrations away from the source. The report discusses the transport of dioxin from a source and presents methods for estimating dioxin concentrations at potential points of exposure away from a source. The transport pathways that were considered to be important were volatilization, suspension and deposition of windblown particles, overland sediment runoff, and in-stream sediment transport. Concentrations at locations away from a source can be estimated using conversion factors for air, soil, and sediment. Concentrations in these media at potential points of exposure can be estimated using the source concentration and factors that describe the physical characteristics of the source and the transport pathways. Because ingestion of contaminated foodstuffs will result in exposure to dioxin, an example is provided for estimating the amount of dioxin in beef. Missouri beef distribution patterns and a market dilution concept were used to estimate potential chronic exposure to contaminated beef products within the state.