Individual Exposure Levels in People Environmentally Exposed to Crocidolite

Abstract

The objective of this article is to assign individual airborne crocidolite exposure levels to former residents of the town of Wittenoom, Western Australia. All environmental monitoring programs carried out in the town since 1966 were reviewed and assessed for their suitability for use in estimating individual exposure to crocidolite. These programs measured respirable fibers greater than 5 μm in length. Duration of residence was determined from questionnaires, work history sheets of the Australian Blue Asbestos Company, and the various sources used to assemble a cohort of previous residents. All exposure measurements were calculated assuming continuous exposure over 24 hours per day, 7 days per week. Intensity of exposure and cumulative exposure were estimated for each person in the cohort. All environmental monitoring surveys carried out at Wittenoom have detected some crocidolite fibers. The levels of fibers have shown a continuing decrease since the mining operations ceased in 1966. Most of the cohort stayed at Wittenoom longer than 1 year and had a median estimated intensity of exposure of 0.5 fibers per milliliter and a median estimated cumulative exposure of 2.8 fiber-years per milliliter. As a result of the crocidolite mining operations at Wittenoom, the residents of the town, even as late as 1992, have been continuously exposed to higher levels of airborne crocidolite than other populations where no such source of contamination exists.