Residential exposure summary methodology for a reproductive health study of multiple hazardous waste sites

Evaluation of associations between residence near hazardous waste sites and rare outcomes requires the consideration of large geographic areas and multiple sources of contamination. For a case-control study of birth defects and solvents, metals and pesticide exposure, the authors rely on previously collected data to rate possible residential exposure from hazardous waste sites. Four pathways of exposure are evaluated: air vapor, air particulates, groundwater ingestion, and groundwater inhalation. Areas within one mile of each site are classified according to 1) the probability of exposure to solvents, metals, and pesticides, and, if available, 2) the relative concentration of contaminants. The probability of exposure (low, medium, or high) for air vapor and particulates depends on the evaporation and soil retention potential of the contaminants, degree of containment, predominant wind direction, and size of the contaminated area. The probability of exposure for groundwater ingestion and inhalation depends on whether there are water supply wells or affected basements within one mile, solubility of the contaminants, direction of groundwater flow, and groundwater sampling results. Relative concentration is based on sampling results for the most commonly sampled media. Exposures are shown on a standard template that defines 25 sectors within a 1 mile radius of each site. The method cannot provide exact estimates of residential exposure, because it relies on data of variable quality. It does provide a basis for evaluating health effects at multiple sites by identifying susceptible residential areas.