Inhalation of asbestos fibers identified as the exposure pathway

On the basis of information from Libby and facilities that processed vermiculite ore from Libby, we have developed a list of possible exposure pathways for vermiculite processing facilities. All pathways have a common source—vermiculite from Libby contaminated with amphibole asbestos—and a common route of exposure—inhalation.

In general, the main pathways are past inhalation of fibers by former workers and nearby residents, and current and future inhalation of fibers from re-suspended dust and soil by residents and on-site workers.

An exposure pathway is the means by which an individual is exposed to contaminants. It consists of the following five elements: 1) a source of contamination; 2) a medium, such as air or soil, through which the contaminant is transported; 3) a point of exposure where people can contact the contaminant; 4) a route of exposure by which the contaminant enters or contacts the body; and 5) a receptor population.

A pathway is considered complete only if all five elements are present and connected. A pathway is considered potential if the pathway elements are (or were) likely present, but insufficient information is available to confirm or characterize the pathway elements. A pathway may also be considered potential if it is currently missing one or more of the pathway elements, but the element(s) could easily be present at some point in time.

An incomplete pathway is missing one or more of the pathway elements and it is likely that the elements were never present and not likely to be present at a later point in time. An eliminated pathway was a potential or completed pathway in the past, but has had one or more of the pathway elements removed to prevent present and future exposures.

Courtesy of the Washington Department of Health