Childhood exposure to Libby amphibole during outdoor activities

Residents of Libby, MT were exposed to amphibole asbestos through multiple environmental pathways. Previous exposure characterization has primarily relied on qualitative report of these exposure activities. The objectives of this study were to describe available data from the US EPA preremediation actions for Libby amphibole (LA) exposure in Libby, MT and develop an approach to characterize outdoor residential exposure to LA among children. Homes in Libby, MT included in the US EPA preremediation Contaminant Screening Survey (CSS) were categorized by the presence of interior and/or exterior visible vermiculite and concentrations of LA were measured in samples of dust and soil. Airborne exposure to LA while digging/gardening, raking, and mowing were estimated using US EPA activity-based sampling (ABS) results. Residential histories and frequency/duration of childhood activities were combined with ABS to demonstrate the approach for estimating potential exposure. A total of 3154 residential properties participated in the CSS and 44% of these had visible exterior vermiculite. Airborne concentrations of LA where there was visible vermiculite outdoors were 3-15 times higher during digging/gardening, raking, and mowing activities compared with homes without visible outdoor vermiculite. Digging and gardening activities represented the greatest contribution to estimated exposures and 73% of the participants reported this activity before the age of 6 years. This methodology demonstrated the use of historical preremediation data to estimate residential exposures of children for specific activities. Children younger than age 6 years may have been exposed to LA while digging/gardening, especially at homes where there is visible outdoor vermiculite. This approach may be extended to other activities and applied to the entire cohort to examine health outcomes.