Technology Transfer Network - Air Toxics Web Site
Dose-Response Assessment for Assessing Health Risks Associated With Exposure to Hazardous Air Pollutants
The information below presents tabulated dose-response assessments that the Office of Air Quality Planning and Standards (OAQPS) uses for risk assessments of hazardous air pollutants. Two separate tables are provided. Table 1 presents values for long-term (chronic) inhalation and oral exposures; Table 2 presents values for short-term (acute) inhalation exposures. It is important to note that only for the purpose of these tables that the compound categories use the CAS number for the element. However, all compounds having that element in their chemical structure are included in the compound category.
The tables compile assessments from various sources for many of the 188 substances listed as hazardous air pollutants ("air toxics") under the Clean Air Act Amendments of 1990. Sources of chronic dose-response assessments were arranged in priority order according to conceptual consistency with EPA risk assessment guidelines and level of peer review. Table 1 shows only the assessment result from the highest-priority source. Accompanying the table is additional information about the table and about decisions we made for several chemicals on the basis of chemical-specific information. For the oral exposure pathway, Table 1 shows only assessment results for persistent and bioaccumulative substances likely to pose important non-inhalation risks when emitted from air sources. Sources of acute dose-response assessments were not prioritized because we judged that many were not directly comparable. Table 2 shows all values from our list of sources.
The numbers in these tables support hazard identification and dose-response assessment, as defined in the National Academy of Sciences (NAS) risk assessment paradigm, for estimating the risk of contracting cancer and the level of hazard associated with adverse health effects other than cancer.
Each assessment in these tables is best visualized as an estimate within a range of possible values, surrounded uncertainty and variability. This range of possible values may change as better data become available. They are generally appropriate for screening-level risk assessments, including assessments to select contaminants, exposure routes, or emission sources of potential concern, or to help set priorities for further research. For more complex, refined risk assessments developed to support regulatory decisions for single sources or substances, we recommend evaluating dose-response in detail for each "risk driver" to incorporate appropriate new toxicological data.