tions. Furthermore, such data are typically based on a few stack samples for each pollutant. The adequacy of such emissions data to characterize fully the contribution of incineration to ambient pollutant concentrations for health-effects assessments is uncertain. More emissions information is needed, especially for dioxins and furans, heavy metals, and particulate matter.

Recommendations

Government agencies should continue to improve—or in some cases should begin—the process of collecting, and making readily available to the public, substantially more information on the following:

  • The effects of design and operating conditions on emissions and ash. Such information should show how specific emissions and ash characteristics are affected by modifying the operating conditions of an incinerator to maximize its combustion efficiency. It should also indicate the types and combinations of operating conditions that optimize the effectiveness of emission-control devices.

  • New combustor designs; continuous emission monitors; emissions-control technologies; operating practices; and techniques for source reduction, fuel cleaning, and fuel preparation, including records of demonstrated environmental performance and effects on emissions and ash.

  • Emission and process conditions during startup, shutdown, and upset conditions. Emissions testing has usually been performed under relatively steady-state conditions. However, the greatest emissions are expected to occur during startup, shutdown, and malfunctions. Such emissions need to be better characterized with respect to possible health effects. Therefore, data are needed on the level of emissions, the frequency of accidents and other off-normal performance, and the reasons for such occurrences.

ENVIRONMENTAL PATHWAYS OF HUMAN EXPOSURE

After pollutants from an incineration facility disperse into the air, some people close to the facility may be exposed directly through inhalation or indirectly through consumption of food or water contaminated by deposition of the pollutants from air to soil, vegetation, and water. For metals and other pollutants that are very persistent in the environment, the potential effects may extend well beyond the area close to the incinerator. Persistent pollutants can be carried long distances from their emission sources, go through various chemical and physical transformations, and pass numerous times through soil, water, or food.

Dioxins, furans, and mercury are examples of persistent pollutants for which incinerators have contributed a substantial portion of the total national emis-



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