WTC environmental health assessment draft, May 2002

NYC 9/11 Public Portal Document

The Tier I level for asbestos in settled dust was based on Millette’s (full name & reference?) K factors, which are empirical relationships between concentrations of asbestos fibers in settled dust and indoor air. Millette developed the K factors by studying matched air and dust samples taken from various homes, at varying levels of activity in the home. The Tier I level was based on the K factor for a worst case scenario of a high level of activity. Although K factors are not rigorous enough to rely upon for a firm health decision, they are used here only to define what might constitute elevated fiber counts, that would need to be addressed as a near-term concern. This approach may overestimate potential exposures, but as such, is protective. .

Tor asbestos in indoor air, the Asbestos Hazard Emergency RcsponserAct (AIlLRA) standard of VO'StTuctures per SQuare millimeters (S/mm2), as measured by Transmission Electron Microscopy (TE]M[)"analysis, has been used since the 1980s to confirm cffcctive^batcrnent of asbestos- containing material in schools. The standard represented the highest detectable level of background contamination on blank fiRcrs- at-the-time (in the 1980s), not a risk-bctSCd analysis.

In order to develop risk-bascdH^TcnchmtrrksM^or~thTS'T*cporty*the AIZGRA standard was compared to a nsk-based approach called Phase Contrast Mici'oscopy (PCIvI). PCM w as used for airborne asbestos analysis in most of the occupational epidemiology studies that provide robust dose- response data on asbesh dated carcinogenesis. AlfLiRA s TEM fiber counts were converted to structures thst would be visualized fidd the nndlysis been done by PCM. It should be noted thnt the correlation between totdl PCM fiber 3,nd TETvl fiber counts is V cry uncci"tciin Hud is likely to vary from one venue to another; therefore, no standard-conversion factor exists-forthesetwo measurements.

Ttle process for estimating cancer risk based on the AtHERA. standard includes 1) harmonizing the standard (TENI counts) with the dosc-rcsponse metriC'(PCNI counts)^ 2) converting units of measurement from fibers'per unit area of filter paper to fibers per unit volume of airl and 3) calculating an airborne asbestos concentration that relates tO”an upper-bound cstimatc-of exposure duration and acceptable risk level.

1) Dels ci ci OH PCM or PCM Equivalence

Quantitative risk assessment based on PCNI assigns cancer potency to fibers greater than 5 um in length with an aspect ratio ^3^1. The AIlLRA standard directs "tlTat''aH'"fibcrs' greater than 0.5 um in length be counted. ThereforcT'theTislcassociatcd™with fibers counts performed as per AUER A IS a function of fiber length distribution with only those fibers > 5 um contributing to risk (i.c., peM-Ckjuivalcncc, or PCME).

A. worst-casc scenario risk analysis can be perfonned on the AIlIiRA standard of 70 S/mm2-by assuming that the entire distribution of fibers is 5 um. An additional clement of conservatism is provided by including in the count extrcnrely thin fibers ('CO.25 um w^idth). Long fibers with width '^0.25 um are, generally, not visualized by PCM^.

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CONFIDENTIAL, CITY_21MC100_003423799 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176170