USE OF LOADING RATES TO ESTABLISH DIOXIN CRITERIA FOR LAND APPLICATION OF SLUDGE

A methodology derived from empirical field and laboratory data on wild life toxicology, chemical concentrations, and loading rates is develop ed for defining criteria for protecting wildlife exposed to landspread materials containing 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and T CDD-like compounds. The method controls mass loading, giving it clear advantages over soil-concentration-based criteria in situations where material is spread in a relatively thin layer on the surface and not i ncorporated into the soil. It also controls dioxin toxic equivalents i n the target organism rather than in the landspread material. It achie ves a high level of protection for bird embryos by applying a safety f actor to a no-observed-adverse-effect level (NOAEL) derived from egg t oxicity data and combining this adjusted NOAEL with bioaccumulation da ta from the most efficient avian accumulator of TCDD on a landspread s ite. Assuming that bird embryos are among the most sensitive organisms to TCDD in the terrestrial environment, dioxin restrictions adequate to safeguard eggs will protect other wildlife inhabiting landspread si tes. Using this methodology, the Wisconsin Department of Natural Resou rces has derived the following wildlife dioxin criterion for surface s preading (i.e., no incorporation) a paper industry sludge: The sum of the mass of TCDD plus 0.0013 times the mass of 2,3,7,8-tetrachlorodibe nzofuran (TCDF) shall not exceed 1.3 mg per hectare.