WTC health criteria appendix, Dec 2001

NYC 9/11 Public Portal Document

Another consideration in setting the target risk level involved the anticipated background level of contaminants such as asbestos, dioxin and PAHs in urban indoor environments. EPA is currently conducting a study to characterize background conditions for COPCs in New York City residential dwellings. In advance of this study, a literature review was conducted to provide a general estimate of background concentrations for carcinogenic COPCs in urban indoor environments. It should be noted that the literature is limited in this regard. For asbestos, ATSDR reports that “measured indoor air values range widely, depending on the amount, type, and condition (friability) of asbestos-containing materials used in the building” [ATSDR, 1995]. In its review ATSDR notes that the studies suffer from lack of common measurement reporting units. Study results have been reported as ng/m\ f/cc (TEM) and f/cc (PCM). Using unit conversion factors recommended by the National Research Council in 1984, ATSDR [1995] reports that the arithmetic mean concentrations of monitoring data from a variety of indoor locations ranged from .00003 - .006 f/cc (PCM). The proposed clearance level for WTC- impacted residential dwellings (.0009 PCM equivalents) is within this background range.

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CONFIDENTIAL, CITY_21MC100_003423734 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176146