Memorandum on asbestos wipe sampling and cancer risk estimation, December

NYC 9/11 Public Portal Document

Conversion of TEM measurements of WTC dusts to the PCM measurements usedfor the health studies.

A problem, or perhaps more an uncertainty, in using Table 3 arises from the fact that the human health studies are correlated to asbestos that was measured by the PCM method, which does not detect smaller fibers. The WTC dusts were measured by EPA using the more sensitive TEM method, which does detect these smaller fibers. •

Since TEM analyses of WTC dusts give higher reading of fibers/structures asbestos than a PCM reading, some would argue that all of the WTC asbestos levels should be divided by some number (made smaller) to make them comparable to the ATSDR studies which used PCM. For the WTC dusts, the ratio of TEM fibers/structures to PCM-equivalent fibers/structures was high, around 80 to 90.'^

I have chosen not to attempt any conversion of TEM measurements to PCM-equivalent measurements for several reasons. First, the older PCM measures used in studies cited by the ATSDR may not, in fact, be smaller than a TEM measurement of the actual asbestos to which the humans were exposed. This is because PCM cannot distinguish between asbestos and other fibrous minerals. Thus, the studies of humans using PCM measurements may actually have overestimated true asbestos exposures because they included non-asbestos fibers. Also, the asbestos fibers to which persons were exposed in these older studies may not have included a substantial fraction of the smaller fibers like the WTC dusts.

Second, as a matter of policy, the federal EPA has issued no guidelines or standards recommending the use of such a conversion in asbestos risk assessments. If such a recommendation were to be issued, it would first undergo extensive internal and external peer review, and be subjected to due process through a notice and comment period. As an individual staff scientist, I would not take it upon myself to lower a risk assessment until such final guidance is issued. As prudent public policy, however, it is always valid for anyone to upgrade a risk assessment based on new, even if imtested, data indicating a greater hazard.

Claim thatJine asbestos particles are not hazardous

Some may argue that the smaller WTC fibers are less hazardous than the larger fibers. To my knowledge, the federal EfA has not addressed this scientific theory and issued any guidance to discount any cancerous effects of fine asbestos fibers. If such a recommendation were to be issued, it would first imdergo extensive internal and external peer review, and be subjected to due process through a notice and comment period. Until such time as this occurs, as a matter of prudent public health policy, it would be inappropriate to downgrade a risk assessment based on this theory. I have also been informed that EPA has no intention of downgrading the risk based on this theory.

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