MEASURING AND EVALUATING EXPOSURES TO NATURALLY-OCCURRING ASBESTOS FROM OFF-HIGHWAY RECREATIONAL ACTIVITIES AT THE CLEAR CREEK MANAGEMENT AREA IN SAN BENITO COUNTY, CALIFORNIA: WHY A FAVORITE FAMILY OUTING MAY BE HAZARDOUS TO YOUR HEALTH

Activity-based personal monitoring was used to measure exposures to naturally-occurring asbestos (NOA) at BLM's Clear Creek Management Area (CCMA) in San Benito County, California. CCMA is a premier off-highway vehicle recreation area which is popular with families and which includes part of the New Idria Formation, a serpentinite rock body which contains a 31,000 acre outcrop of naturally-occurring asbestos. Motorcycle, ATV, and SUV riders were equipped with personal monitoring equipment to measure asbestos levels in adult and child breathing zones as they rode over recreational riding routes at the CCMA. Air samples were analyzed by the ISO 10312 TEM method and the Phase Contrast Microscopy Equivalent (PCME) fiber size classification (> 5 microns long, 0.25 – 3.0 microns wide, > 3:1 aspect ratio) was used to evaluate the exposures.

Results: Asbestos was found in all personal and ambient air samples. Chrysotile asbestos was the predominant asbestos type found in the air samples, but almost 8% of the fibers detected belonged to the amphibole asbestos group. Motorcycle riding, ATV riding, and SUV driving/riding had the highest exposure concentrations, in some cases exceeding even the OSHA 30-minute Excursion Limit for asbestos. Child exposure concentrations exceeded that of the concurrent adult sample 64% of the time. When risk estimations were calculated for typical CCMA use scenarios, there was no combination of scenario, toxicity value, or visits per year that was below the lower end of EPA’s acceptable lifetime cancer risk range of 10^-6 and the highest risks were calculated at 2 x 10^-3.

Observations: As with El Dorado Hills, EPA’s results were not well received by the stakeholder community. BLM has closed CCMA pending completion of an EIS to determine what uses of the area can be allowed without compromising public health. Questions have been raised regarding the health effects of chrysotile asbestos and whether EPA misidentified amphibole fibers.