Exposure to PCDDs/Fs: Relative Importance of the Diet and of Soil, 1999 Environmental Conference Proceedings

Michael Moore, Lisa Yost, Walter J. Shields & Catherine Petito Boyce

Exponent

John A. Maloy

Ketchikan Pulp Company

Analysis of recent studies on polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) in food, soil, water, and air indicates that food, especially dairy products, meat, and fish, is the primary source (i.e., greater than 95 percent) of human background exposure to PCDDs/Fs. Incremental exposures to PCDDs/Fs in soils near a sulfite pulp mill potentially affected by past deposition of flyash from power boilers were considered in the context of these background exposures. PCDDs/Fs in soil make up only a small proportion of total background exposure. In areas with PCDDs/Fs in soils at a background concentration of 7.4 ng/kg (7.4 pg/g or ppt), total exposure was estimated at 111 pg/day; an increase in the soil concentration to 62 ng/kg (62 pg/g) identified in offsite soils near the mill increased the total exposure only to 117 pg/day. These findings were included in the risk assessment for the pulp mill to provide context in evaluating risk estimates related to PCDDs/Fs in soil. The relative importance of background exposures to PCDDs/Fs in application of the U.S. Environmental Protection Agency’s recent soil cleanup levels of 1 µg/kg (1,000 pg/g) for residential sites and 5–20 µg/kg (5,000–20,000 pg/g) for industrial sites is also explored.