the consequences of sustained exposure. There is some indication from acute and short-terms studies that irritant responses to formaldehyde are lessened by acclimatization.

The epidemiologic studies considered in the draft IRIS assessment are primarily cross-sectional studies and subject to the general weaknesses that affect studies of this design, including the simultaneous measurement of exposure and outcome. Many of the studies involved exposure in residences, and the exposure-assessment protocols covered only a brief time window, leaving the possibility that exposures were misclassified. Furthermore, few of the studies took into account potentially confounding exposures, such as secondhand smoke or other air pollutants. The epidemiologic studies do have the advantage of assessing the risks of formaldehyde exposures as they are experienced on a chronic basis. The study populations cover the range of susceptibility and, to the extent that the effects of formaldehyde exposure are modified by interactions with other agents, the exposure to formaldehyde is experienced along with exposure to the many other contaminants in indoor air.

Given the quite different strengths and weaknesses of the two lines of research, the findings from chamber studies and epidemiologic studies should be considered as complementary. The draft IRIS assessment sets aside the chamber studies as less relevant to derivation of candidate RfCs, but the findings from the studies could be useful, and the committee does not concur with EPA's decision to set them aside. Specific recommendations are provided below for the individual health outcomes.

IRRITATION

Formaldehyde is a reactive gas that has been consistently shown to be an eye, nose, and throat irritant. Sensory irritants act at the sensory fibers of the trigeminal nerve in the nose and upper respiratory tract. Sensory-irritation end points include self-reported sensations of pain, burning, or itching and objective measures of eye-blink counts and lacrimation (Doty et al. 2004). Although EPA’s review focuses on eye, nose, and throat irritation, other types of irritation, such as dermal irritation, have been reported. EPA selected sensory irritation as a candidate critical effect on the basis of concentration-response relationships between formaldehyde and eye irritation observed in three epidemiologic studies of residential populations.

Study Identification

EPA identified many studies that evaluated sensory irritation in response to formaldehyde exposure in residential, occupational, and clinical settings in humans and in experimental animal studies. Human studies evaluated sensory irritation responses in the eyes, nose, and throat after exposure to formaldehyde at 100-3,000 ppb and for durations ranging from 90 sec in chamber studies to



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