EVALUATING THE HEALTH IMPACTS OF INCINERATOR EMISSIONS

Before a municipal solid waste incinerator (MSWI) can be operated, it is generally required that a health risk assessment be performed and t hat human health risks predicted fall below permissible levels. There are several components to the risk assessment paradigm, including: (1) determination of stack emissions for potentially toxic chemicals, (2) calculation of atmospheric dispersion and exposure point concentratio ns, (3) development of scenarios by which humans become exposed to air borne chemicals, (4) identification of dose-response functions for car cinogenic and noncarcinogenic effects, and (5) prediction of the proba bility of health impacts. Typical MSWI air contaminants of concern are metals (e.g., Ag, As, Be, Cd, Cr, Hg, Ni, Pb, Sb) and organic compoun ds (e.g., benzene, PCBs, B(a)P, polychlorinated dioxins/furans). MSWI risk assessments include both direct exposure pathways (air inhalation , incidental ingestion of soil), and indirect pathways (food-chain exp osures such as human consumption of produce, beef, fish, and milk). To perform a risk assessment for direct and indirect routes of exposure, both atmospheric concentration and deposition rate are required; assu mptions need to be made about toxicity as a function of route of expos ure. Interpretation of risk-assessment results requires understanding how some of the conservative assumptions made in the risk-assessment p rocess play out relative to real-world health hazards. Some attempts h ave been made to verify that predicted concentrations of airborne cont aminants are reflected by measured levels, but in most cases the predi cted air and soil concentrations fall below limits of detection and al ways within background variability. In summary, health risk assessment s are useful for regulatory guidance, but it has not been possible to verify that health risks of MSWI emissions contribute measurably to po pulation health risks.