Research Program Area: Health & Exposure
A method for collecting and analyzing silica fibers in air has been developed. Environmental release of amorphous silica fibers by rice harvest, rice straw and stubble burning and field preparation after burning has been demonstrated. Fiber were irregularly shaped, often having no parallel sides, and did not appear to be hair like or needle like. Aspect ratios seldom exceeded 20:1 and aspect ratios of 5:1 were more common. Airborne levels for employees conducting these operations, which are likely to exceed exposures to the public, has been demonstrated up to 22.9 x 106 fibers per cubic meter of air, using a respirable fraction sampling head (not a PM10 sampling head). Silica fibers were found downwind of field edge and in urban areas in the vicinity of rice straw burning. Result indicate that decreased burning is likely to reduce the levels of respirable amorphous silica fiber emissions from rice farming, but that rice harvest and field preparation are likely to continue to be significant sources of emissions. Further work will be needed to devise sampling and analytical methods which are less sensitive to field conditions and less time consuming and to characterize the potential health effects of respirable amorphous silica fibers and fiber emissions.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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