DIOXIN IN ORGANIC RESIDUALS

The land application of the organic residuals generated during the treatment of wastewater represents a viable recycling alternative for management of these “wastes” and an opportunity to improve soil fertility. When sewage sludge, the semi-solid residual created during the treatment of municipal wastewater, is treated to kill pathogens and is determined to meet federal standards for trace metal concentrations, it is considered “biosolids”. Approximately 54% of the sewage sludge generated in the U.S. is returned to the soil as biosolids to increase soil nutrient concentrations and organic matter content. Pulp and papermill sludges are also a potential source of soil organic matter and nutrients when recycled in land application programs. While much of the early research regarding the safety of land application programs has focused on trace metal content and pathogen reduction, concerns related to the presence of dioxin in sludges have recently received much attention. The toxicity of dioxin to humans is the focus of intense debate, but it is clear that dioxin is a very potent carcinogen in some animals. The purpose of this paper is to give an overview of the sources of dioxin in the environment and in wastewater treatment residuals, review the behavior of dioxin in sludges and soils, and look at studies addressing the potential environmental impact of land applying organic residuals containing dioxin.