Exposure to hazardous air pollutants in homes
Prior studies have found that human exposure to hazardous air pollutants (HAPs) occurs in homes; however, the depth of these assessments was limited by the extent of the analyzed data. The present Ph.D. dissertation focused on air contaminants of concern in residential buildings, the possible sources of these pollutants, and population subgroups with greater contaminant risk. This research also evaluated the effects of building characteristics and household activity patterns on indoor pollution and risk levels. To this end, an in-depth analysis was performed of data from the Relationships of Indoor, Outdoor and Personal Air (RIOPA) study, one of the most comprehensive exposure assessments to date.
Using personal concentrations from the RIOPA study, a cancer risk assessment was performed to identify both important pollutants and populations at higher risk. The analyzed compounds were acetaldehyde, benzene, chloroform, carbon tetrachloride, p-dichlorobenzene (p-DCB), ethylbenzene, formaldehyde, methylene chloride, methyl tert-butyl ether (MTBE), styrene, trichloroethylene and tetrachloroethylene. Results indicate that Hispanics and non-Hispanic whites had median cumulative cancer risks (CCR) of 520×10-6 and 440×10-6, respectively, for which the main contributors were formaldehyde, p-DCB, acetaldehyde, chloroform and benzene. Statistically significant differences in CCR between and within Hispanic and whites were primarily due to exposures to p-DCB. Exposure to formaldehyde was further investigated because this compound was the largest contributor to CCR for 69% of Hispanics and 88% of whites, and because most participants had similar cancer risks from these exposures (median = 260×10-6, coefficient of variance = 28%). Results suggest that the U.S. population may be experiencing chronic exposures because of long-term formaldehyde emissions from pressed-wood materials bound with urea-formaldehyde resins. Source removal may be the most effective way to decrease these chronic exposures. Benzene was also examined further because it is a known human carcinogen. Results show that indoor benzene concentrations increased as the proximity of parked vehicles decreased. Residing in a home with an attached garage could lead to exposures to benzene ten times higher than while commuting in a car in heavy traffic, and with mean excess cancers of 17×10-6. Detached garages could reduce health risks from exposure to benzene and other gasoline-related pollutants.