These sources of variation could result in exposure

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preceding rider, height of rider, etc. These sources of variation could result in exposure concentrations greater or less than those observed during this sampling event. This uncertainty was addressed by performing each sampling scenario (e.g., ATV riding at the tail of three riders) more than once per day and on consecutive sampling days, to obtain a range of asbestos air concentrations for each scenario within a sampling event. Risks were then estimated based on minimum and maximum chronic exposure concentrations that were derived from the measured minimum and maximum air concentrations. Due to logistic and cost considerations, sample sizes were limited. Therefore, it is likely that the observed range in exposure concentrations is narrower than would be observed if more samples had been taken with a variety of riders and riding styles. ° Child vs. Adult Exposures . Children may experience different exposures than adults for three reasons: First, they are shorter, so their distance from the asbestos source (ground) is less than for adults engaged in the same activity. Second, they tend to be trailing, rather than lead motorcycle or ATV riders. Third, in the case of SUVs, children will often ride in the back, rather than front seat. To address this source of uncertainty, asbestos filter cassettes were placed on adult study participants at heights to simulate a child’s breathing zone. In the SUV scenario, filter cassettes were placed on the backrest of the back seat to simulate a child’s breathing zone. ° Scenario Routes . Exposure concentrations could, potentially, vary with the route traveled during the sampling activity. The potential for variability within a particular activity scenario (motorcycle, ATV, SUV, hiking) was limited by selecting routes for each scenario and repeating those routes, to the extent possible, during all sampling events. This approach reduced sampling variability within activity scenarios (e.g. ATV riding). However, different routes were selected for each activity (the ATV route was different from the SUV route), which could contribute to variability in asbestos concentrations across scenarios. To address this source of variation, soil samples were taken along each route and analyzed for soil moisture and asbestos concentration, since these parameters could, potentially, be linked to differences in asbestos dust generation. Soil samples were collected from discrete sample locations but activities, by their nature, integrated over a larger area and are representative of actual exposures. The results of soil sampling will be presented and interpreted in a future report. ANALYTICAL UNCERTAINTY Overloaded Filters . The analysis of asbestos fibers on filters has inherent limitations and uncertainties. If samples are overloaded with asbestos fibers or dust, it may not be possible to analyze them accurately. To address this concern, since overloading of the filters can only be determined by the analytical laboratory, two different
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12 sample volumes were collected concurrently for each sampling event, based on anticipated air concentrations from previous site-specific experience.
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  • Fall '17
  • CCMA, unit risk

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