Dioxins: Threat Versus Reality - A Case Study at a Sulfite Pulp Mill, 1999 Environmental Conference Proceedings

Lisa Yost, Nicholas Gard, Walter J. Shields, Lucinda Jacobs & Michael Moore

Exponent

John A. Maloy

Ketchikan Pulp Company

Potential human health and ecological risks associated with exposure to polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) remain a central public concern and impetus for agency responses at bleached pulp mills. This paper examines the relative importance of PCDDs/Fs as a health risk for human and ecological receptors at a dissolving sulfite pulp mill, which recently closed in southeast Alaska. Key issues were recognizing multiple offsite sources in the sampling strategy and applying a realistic seafood consumptino rate. An uncertainty assessment demonstrated that consumption of PCDDs/Fs in the typical U.S. diet results in far greater human exposure than that related to the site. Upland ecological issues were assessed with the use of a food-web model: marine ecological evaluations included food-web modeling and sediment bioassays. Despite use of conservative U.S. Environmental Protection Agency methods, neither assessment identifies PCDD/F risks above identified acceptable risk levels. In contrast, localized upland areas had elevated human health risks related to arsenic in soil (probably from crushed gravel onsite). Similarly, observed toxicity in marine sediments was attributed to sulfide and ammonia (natural products of organic matter degradation). While PCDDs/Fs continue to be the focus of public concern and involvement, the remedial actions approves by regulatory agencies have been based on identifies risk levels.