the potential effect of the average incinerator is expected to be minimal; however, a maximally polluting facility could add substantially to the mercury burden in the community. The implementation of MACT technology is expected to reduce exposures to mercury at the local level. Air concentration estimates related to incineration (Pre-MACT and Post-MACT) are based on Table 4-8, Table 4-9, Table 4-10 through Table 4-11 in Chapter 4.

Acidic Gases and Acidic Aerosols

Incinerators directly release both acidic aerosols and gases, as well as acidic aerosol precursors that can be transformed into acid particles in the atmosphere. The acidic gases and vapors released from incinerators are generally of less concern than acids released or formed as aerosols (such as H2SO4). Thus, water-soluble acidic gases and vapors (such as SO2, HCl, and HNO3), are of low concern because, at ambient concentrations, these are efficiently “scrubbed out” in the trachea before reaching the lung. Particularly strong acidic aerosols, such as those containing H2SO4, however, more readily reach into the deepest recesses of the lung and are of greater health concern at ambient concentrations.

Acids released from incinerators therefore warrant a varied degree of concern depending on the form of the acid (particulate or gaseous) and the extent of emission (pre or post compliance with MACT). Acidic gases are of minimal health concern to the local population and of negligible concern at the regional level but represent a moderate concern to workers, given that exposures have the potential to become high. Compliance with MACT regulations further diminishes the concern regarding acidic gases at the local and regional levels, but not in the worker environment.

Acidic aerosols are associated with a somewhat higher degree of concern because of their particulate form and because MACT regulations are not directly aimed at reducing them. However, the acidity concern is reduced after MACT implementation because some MACT controls (such as SO2 limitations) can be expected indirectly to lower strongly acidic aerosols resulting from such plants.

Carbon Monoxide

Because only about 1% of all CO emissions are attributable to incineration (EPA 1998b,c), the incremental exposure to CO from incinerators is not considered to represent an important increment at either the local or regional level. Although it is possible for workers to be exposed to high levels of CO from incomplete combustion, no data are available to indicate that this has occurred.

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