underlying risk estimates and is not necessarily an endorsement, for example, of using a specific cancer, such as leukemia, for a consensus risk estimate. The committee’s opinions on mode of action and weight of evidence concerning specific health outcomes are given in Chapters 3-5 of the present report.

FORMALDEHYDE REFERENCE CONCENTRATIONS

EPA defines an RfC as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime” (EPA 2010a). That is, an RfC is a concentration at which exposures would be allowed to occur with sufficient certainty, taking into account susceptibility and variability, that adverse outcomes would not result. RfCs are used by EPA, state agencies, various regulatory agencies, and other entities to develop allowable ambient air concentrations and to evaluate risks posed by current and potential exposures.

The draft IRIS assessment proposes several RfCs for formaldehyde that are based on “three studies of related health effects: asthma, allergic sensitization, pulmonary function, and symptoms of respiratory disease in children from in-home exposure to formaldehyde” (Rumchev et al. 2002; Garrett et al. 1999; Krzyzanowski et al. 1990) (EPA 2010b, p. 5-66). The discussion concludes by presenting a range (1-9 ppb), rather than a specific value, for the RfC. The committee was asked to comment on values of the uncertainty factors used to derive the RfCs that account for human population variability and for deficiencies in the overall database (see Box 1-1).

Chapters 4 and 5 of the present report addressed the health effects associated with formaldehyde exposure and reviewed the candidate critical effects, relevant studies, and points of departure identified by EPA. EPA’s process for developing the RfC for formaldehyde is illustrated in Figure 6-1. The following sections briefly summarize EPA’s selection of critical effects and key studies and identification of points of departure for derivation of candidate RfCs. Information that is relevant to evaluating the uncertainty factors proposed by EPA is then presented, and the committee provides its recommendations for those factors. Finally, the committee comments on the IRIS process for derivation of RfCs and provides suggestions for improving the process of selecting a final RfC.

Selection of Candidate Noncancer Effects

Health effects associated with formaldehyde exposure have been studied extensively in people, laboratory animals, and in vitro systems with a variety of study designs. EPA evaluated a broad array of health effects that the committee



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