Q&A and FAQ regarding WTC response, Oct 2001

NYC 9/11 Public Portal Document U.S. fei-Hzitwr

fibrogenic activity, while short fibers have lower fibrogenic activity. This relationship may be associated with the inability of macrophages to engulf and remove fibers that are significantly larger than themselves.” However, this same reference also states: ‘‘Results from human studies suggests that short asbestos fibers also may be important in cajising pulmonary fibrosis. These studies showed that, in groups of chrysotile miners and millers and amosite-exposed shipyard and insulation workers with asbestosis, histologically-graded fibrosis was positively correlated with mean fiber concentration in lung tissue, but was negatively correlated with mean fiber length.” More research is needed on the role of short fibers (5’ um ? rd less) in asbestosis induction. It should be ne ed, however, that the AHERA standard of 70 (which counts fibers >.5 um) is v/cll below the asbestos concentration associated with asbestosis. t

15. (Cancer risks for Libby compared to Lower Manhattan)

issue - Risk calculations from the Libby Endangern.ent Assessment (12/20) are coiapared to risk estimates from hypothetical scenarios at the WTC.

Response - The risk calculations from the Libby Endangerment Assessment were based on actual asbestos air sampling results (analyzed by TEM) which were subsequently converted to PC.ME fiber counts. Risk calculations for hypothetical exposure scenarios associated with the WTC have been performed and were based on the asbestos load (f/cm2) of settled dust, rather than air samples. As previously mentioned, the relationship between asbestos concentration in settled dust and ambient air is highly variable and depends on dust re-entrainment potential and ambient conditions (e.g., air exchange rates) as well as asbestos load (i7cm2). In addition, since there was no air sampling for the WTC risk calculations, the conversion to PCME relied on limited indoor sampling data from secondary sources to arrive at a PCME estimation of 20% of total TEM fibers. The 20% value represents the upper bound of the range (1.3% - 20%) of correlations between PCME and total TEM fiber counts from the aforementioned indoor sampling data. Thousands of asbestos air samples in the ambient air collected by EPA since 9/11 indicate that PCME is less than 10% of total TEM fiber counts.

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