In the context of a chemical incident, human exposures may occur to chemicals via contaminated air, drinking water, soils or surfaces.122 For any of these materials and surfaces, human exposures to chemicals may occur through inhalation, ingestion and/or dermal contact. Generally, the primary exposure pathways of concern are inhalation of contaminated air, ingestion of contaminated drinking water, incidental ingestion of contaminated soil, and/or dermal contact with contaminated surfaces.
Some chemical contaminants may contribute exposure via other pathways (i.e., inhalation of a volatile chemical from soil, surface or water; dermal absorption from surface water). In such cases, a multi- pathway risk assessment approach should be used.
Health-based exposure guidelines for workers and the general population are needed to appropriately plan for potential risks resulting from chemical incidents. A number of organizations have developed short-term and long-term exposure guidelines, each with a specific purpose, target population(s) to protect, exposure scenarios (e.g., accidental releases, workplace, environmental screening), and severity of adverse health effects considered in their development.123
Selection of appropriate health-based exposure guidelines is complicated by several factors, including the following:
- Multiple sources of available exposure guidelines for the same substance
- Differences in exposure guidelines with respect to exposure duration
- Differences in the target population (occupational verses general population)
- Differences in the intended uses of the exposure guidelines
- Variations in the applicable averaging exposure times among exposure guideline
- Differences in the severity of potential health effects associated with the various exposure guidelines
- Gaps in available exposure guidelines.