Table 1.

U.S. Environmental Protection Agency’s Criteria for Designating At-Risk Populations^a

Under the definition of at-risk population, based on the EPA Administrator’s judgment, a population need meet one of four criteria with adequate evidence (Federal Register, 2013):
(1) Higher levels of exposure;
(2) Higher dose at a given level of ambient exposure;
(3) Increased adverse effects at a given level of ambient exposure; and
(4) Increased health effects due to continuum of effect among sensitive members of a populationb
Different criteria for identifying and evaluating evidence for designation of vulnerable at-risk
populations were used in the two most recent NAAQS review processes. Specifically, in the Ozone NAAQS review (2014), EPA used a three-part definition for inclusion and did not account for more adverse effects due to already compromised health, a criterion articulated in the American Thoracic Society statement. The evidence was arrayed with a more informative four-level scale (adequate, suggestive, inadequate evidence, and evidence of no effect). By contrast, in the PM NAAQS review (2012), EPA used a broader set of criteria, but a binary scale to evaluate the evidence; essentially, a population was either considered an at-risk population or a healthy comparison group.

^aIn EPA’s Integrated Science Assessment, the staff practice is to require a demonstration of harm in the peer-reviewed literature as a screening step—that air pollution is harming a population—before assessing that group against the criteria.

^bIn the ozone NAAQS review, EPA only included the first three criteria for the development of the revised ozone NAAQS. Although contained in the American Thoracic Society (ATS) statement (American Thoracic Society, 2000), EPA’s Ensuring Risk Reduction in Communities with Multiple Stressors: Environmental Justice and Cumulative Risks/Impact (NEJAC, 2004) and applied in previous NAAQS reviews, the fourth criterion was omitted from correspondence with EPA Administrator Lisa Jackson in the February 2013 memo to CASAC which documented Agency policy (U.S. EPA, 2013). The rationale for not including the fourth criterion of population consequence was not discussed.