Typical Dioxin Concentrations in Agriculture Soils of Washington State and Potential Sources

Background or typical levels of polychlorinated dibenzo-p-dioxins and of polychlorinated dibenzo-p-furans in soils have become increasingly important in the regulatory community, as dioxins have come under increased scrutiny due to their toxicity and persistence. Knowing the typical levels of dioxin in soils is important to set regulatory levels, to prevent further contamination, and for setting cleanup levels. A random sample (n = 54) of agricultural lands within Washington state revealed a typical concentration of “dioxin” of 0.14 ng/kg (toxicity equivalents, TEQ). For a comparison, residential urban areas, forested, and open areas were also investigated on a smaller scale (n = 14, 8, and 8, respectively) with typical dioxin values of 4.1, 2.3, and 1.0 ng/kg (TEQs), respectively. A discriminant function analysis was used to examine soil dioxin profiles and associations with potential known dioxin sources in Washington state. Soil sample dioxin profiles could not be discriminated from those of biosolids and pentachlorophenol products.