SETTING DIOXIN EMISSION LIMITS FOR MSW-INCINERATORS - A MULTIMEDIA EXPOSURE ASSESSMENT FRAMEWORK

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzof urans (PCDFs) are emitted in trace amounts from municipal solid waste (MSW) incinerators. The exposure to PCDD/Fs experienced by an individu al is dominated by the food chain pathway, which accounts for over 98% of the total uptake. Defining a target daily intake (the World Health Organization TDI of 10 pg I-TEQ kg.bw(-1) day(-1)) exposure assessmen t algorithms were then applied to arrive at the corresponding PCDD/F l evels in air, soil, plants, food products, etc., which would allow the target intake to be met while retaining the balance of intake between the Various exposure pathways. These concentrations were converted to an ambient air concentration of PCDD/Fs and ultimately, by defining c riteria for acceptability, to a guide value for PCDD/F concentration i n emissions from the MSW incinerator. This strategy was applied to PCD D/F emissions from MSW incinerators of various sizes against two illus trative criteria for acceptability: an ''insignificant'' release and a threshold above which the release may require further assessment for environmental effects and for control. Using the criteria developed in this paper, the current PCDD/ F emission limit of 0.1 ng I-TEQ m(-3) results in an emission that is classed as ''insignificant'' for all pl ant sizes. However, higher emission concentrations can also be accommo dated below the threshold for further assessment and control. (C) 1997 ISWA.