FIGURE 3-4 Physical and biological routes of transport of hazardous substances, their release from disposal sites, and potential for human exposure. Source: Adapted from Grisham, 1986, with permission.

environment exposure to volatile organic compounds (VOCs). For example, Andelman (1990) has developed an indoor air model validated by air measurements of TCE from residential bathrooms. He found that TCE inhalation exposures from a six-minute shower are comparable to ingestion of TCE in drinking water. Jo et al. (1990a,b) found that breath concentration after showering was approximately twice as high as that after inhalation-only exposure; thus dermal absorption was equivalent to inhalation absorption.

Percolation of VOCs into the home from contaminated soil under or around houses is another pathway for exposure. For example, at Love Canal, New York, migration of chemical leachates through the soil and evaporation through porous basement walls resulted in the presence of benzene, toluene, chloroform, TCE, PCE, and hexane in the air inside homes (Paigen et al., 1987).

Lioy (1990) has pointed out that contaminant exposure through ingestion of soil and inhalation of dust from soil has begun to receive attention (Pierce, 1985; Travis and Hattemer-Frey, 1987; Severn, 1987). Estimates of the quantity of soil ingested by children and adults have been made (Lioy, 1990). Daily ingestion rates range from milligrams per kilogram of body weight per day to grams per kilogram per day and are important for estimating exposure. Exposure to soil dust through inhalation has received little attention.

The relevance of the total environmental exposure model in assessing exposure to risk from hazardous-waste sites has been illus-



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