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

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are emitted in trace amounts from municipal solid waste (MSW) incinerators. The exposure to PCDD/Fs experienced by an individual 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^?1day^?1) exposure assessment algorithms were then applied to arrive at the corresponding PCDD/F levels 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 criteria for acceptability, to a guide value for PCDD/F concentration in emissions from the MSW incinerator. This strategy was applied to PCDD/F emissions from MSW incinerators of various sizes against two illustrative 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^?3results in an emission that is classed as “insignificant” for all plant sizes. However, higher emission concentrations can also be accommodated below the threshold for further assessment and control.