To determine whether residents of the Third Cliff area or the town of Scituate as a whole were, are, or could be exposed to levels of chemicals in the water supply that may potentially
produce adverse health effects, an exposure pathway analysis was conducted. The exposure pathway analysis is an evaluation of the environmental and human components that lead to exposure. The pathway analysis consists of five elements: a source of contamination, transport through an environmental medium (e.g., air, soil, water), a point of exposure, a route of human exposure, and an exposed population.
Exposure to a chemical must first occur before any potential adverse health effects can result. Five conditions must be present for exposure to occur. First, there must be a source of that chemical. Second, a medium (e.g., water, soil, sediment, air) must be contaminated by either the source or by chemicals transported away from the source. Third, there must be a location where a person can potentially contact the contaminated medium. Fourth, there must be a means by which the contaminated medium could enter a person’s body (e.g., ingestion, inhalation and dermal absorption). Finally, the chemical must actually reach the target organ susceptible to the toxic effects caused by that particular substance at a sufficient dose and for a sufficient exposure time for an adverse health effect to occur (ATSDR 1993).
A completed exposure pathway indicates that exposure to humans occurred in the past, is occurring in the present, or will occur in the future. A completed exposure pathway exists when all of the above five elements are present. A potential exposure pathway exists when one or more of the five elements is missing or uncertain and indicates that exposure to a contaminant could have occurred in the past, could be occurring in the present, or could occur in the future. An exposure pathway can be eliminated if at least one of the five elements is missing and will not likely be present in the future. The discussion that follows incorporates only those exposure pathways that are important and relevant to this evaluation in Scituate.