Independent samples and there is no reason to expect

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independent samples and there is no reason to expect one count to be more reliable than another Recount different grid (RD) - Average the recounted sample results for same reason as for the RS sample results Interlab (IL) - Average the result of the interlab sample results with the result of the original sample (not QC), since they are independent samples and there is no reason to expect one count to be more reliable than another Repreparation (RP) - Average the result of the repreparation sample with the result of the original sample (not QC), since they are independent samples and there is no reason to expect one count to be more reliable than another Verified Analysis (VA) – Use Verified Analysis result over original sample results Field Duplicates – Take the average of the sample results, since they are independent samples Table A2 provides a summary of the multiple sample results and the action taken. Asbestos Dose-Response: The EPA weight of evidence classification for asbestos is known human carcinogen (Table 7). The basis of the classification, the observation of increased mortality and incidence of lung cancer, mesotheliomas, and gastrointestinal cancer in occupationally exposed workers, are consistent across investigations and study populations (U.S. EPA, 2007a). The U.S. EPA IRIS inhalation unit risk for asbestos is 2.3E-01 (f/ml) -1 [fibers/milliliter] -1 . According to EPA guidance, the unit risk should not be used if the air concentration exceeds 4E-02 fibers/ml, since above this concentration the slope factor may differ from that stated (U.S. EPA 2007a). In this risk assessment the calculated chronic exposure concentrations were compared to 4E-02 fibers/ml and none of the values were found to exceed that value. The unit risk is based on fiber counts made by phase contrast microscopy (PCM). In this study PCM equivalent (PCMe) fibers are measured using transmission electron microscopy (TEM) and are defined as asbestos fibers > 5 microns long, > 0.25 microns and < 3 microns in width, with an aspect ratio > 3:1. These dimensions are used because they are equivalent to the range of fiber dimensions that can be detected with PCM. The Cal/EPA OEHHA (Office of Environmental Health Hazard Assessment) inhalation unit risk for asbestos of 1.9 (f/ml) -1 was also used in the risk calculations as a comparison to the IRIS inhalation unit risk results. It is useful to compare the two unit risk results because the two values can be used to bracket the range of toxic effects from asbestos exposures at CCMA. IRIS used a combination lung cancer and mesothelioma model for the population whereas OEHHA used mesothelioma incidence in non-smoking females only for its derivation. Also, OEHHA considers different health endpoints than IRIS. The quantitative unit risk estimate is limited by uncertainty in the exposure estimates, which results from a
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7 lack of data on early exposure in occupational studies and the uncertainty of conversions between various analytical measurements for asbestos (U.S. EPA, 2007b).
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