Draft document with asbestos data tables, DEP Box 09

NYC 9/11 Public Portal Document

DRAFT RBC = TR * (EPC / Risk) Where; RBC = Risk-based Concentration (fibers/mL) TR = Target Risk (unitless) EPC = Exposure Point Concentration (fibers/mL) Risk = Risk resulting from input of EPC into exposure assessment models (unitless)

Uncertainty The main source of uncertainty stems from the analytical techniques used to determine asbestos concentration in air. In the studies referenced in IRIS, Phase Contrast Microscopy (PCM) was used to provide asbestos in air concentrations for determination of the unit risk factor. The criteria used to identify fibers, using PCM methodology, do not distinguish between asbestos fibers and other fibers. While it is most appropriate to used PCM data in risk assessments that employ the unit risk factor listed in IRIS, it is possible that airborne asbestos concentrations provided by PCM would cause an overestimation of risk if other fiber types were present.

Transmission Electron Microscopy (TEM) is selective for asbestos; however, the asbestos IRIS file states that the correlation between PCM and TEM results is difficult to pin down. The effect of applying the unit risk factor listed in IRIS to TEM results can result in either an overestimation or underestimation of risk. The IRIS file also cautions against using the listed unit risk factor with airborne asbestos greater than 0.04 fibers/mL citing uncertainty in the dose-response curve.

Four of the data points from the FDNY data set are TEM results reported in structures per square centimeter (s/cc). In some studies, the structure of the asbestos fiber is considered a factor in its ability to cause cancer. Asbestos analysis by TEM reporting results in s/cc does not provide a distinction between fibers and particles. As a result, in some cases, the use of TEM data reported in s/cc would tend to overestimate the cancer risk. Further, the IRIS file for asbestos does not provide quantitative data for assessing other health endpoints, such as asbestosis. The lack of such data prohibits this risk assessment from quantitatively evaluating asbestosis as a health endpoint resulting in an underestimation of risk.

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