Community Exposure to Asbestos From a Vermiculite

Western Mineral Products/W. R. Grace operated a vermiculite plant in a mixed industrial/ residential area of northeast Minneapolis from 1936 to 1989. The plant processed vermiculite ore contaminated with amphibole asbestos from a mine in Libby, MT. Air monitoring in the early 1970s found fiber concentrations in excess of 10 fibers per cubic centimeter of air (f/cc), indicating that worker exposure to asbestos was occasionally 100 times the current occupational standard. Residents of the surrounding community also had direct contact with vermiculite processing wastes (containing up to 10 % amphibole asbestos) that were made freely available. Children played on waste piles and neighborhood residents hauled the wastes away for home use. In total, 259 contaminated residential properties have been found to date. Reported emission factors and plant process data were used as inputs to model airborne emissions from the plant over several operating scenarios using the U.S. Environmental Protection Agency (EPA) ISC-Prime model. Results estimate short-term air concentrations of asbestos fibers in residential areas nearest the plant may have at times exceeded current occupational standards. Exposure estimates for other pathways were derived primarily from assessments done in Libby by the U.S. EPA. The Northeast Minneapolis Community Vermiculite Investigation (NMCVI) was conducted by th