EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

concentration in settled dust ranged from 101 - 625 parts per million (ppm). By itself, this range does not represent extraordinarily high concentrations, but in combination with the mass of material released from the collapse of the towers, it represents a potentially significant increase in the mass of lead deposited in lower Manhattan. Therefore, lead is included as a COPC.

PAHs. Limited ambient air sampling was conducted for PAHs during the period of time (September through December, 2001) when combustion processes were occurring at the site. However, concentrations in bulk dust [EPA, 2002a and Lioy, 2002] exceeded the removal guidelines for soil in EPA’s Hazard Evaluation Handbook [EPA, 1997] of 9 ppm based on benzo(a)pyrene equivalents. This value is risk-based, equating to an excess lifetime cancer risk of 1x10^ over a 30-year exposure duration for residential settings. Therefore, PAHs are included as a COPC.

Dioxin. Ambient air samples exceeded EPA’s screening criteria (see Appendix B) at various sampling stations during September and October, 2001. Data trend analysis for dioxin in ambient air [EPA, 2002a] showed that concentrations significantly exceeded the risk-based screening level of 0.001 - 0.005 ng/m’. This range was based on an excess lifetime cancer risk of 1x10"* over a 30 year exposure duration for residential settings, using both the existing cancer Slope Factor [Integrated Risk Information System (IRIS), 2002] and proposed cancer Slope Factor in EPA’s draft dioxin reassessment [EPA, 2001]. Therefore, dioxin (and related congeners) is included as a COPC.

Building Materials (Asbestos, Fibrous Glass, Crystalline Silica)

The evaluation of building materials for inclusion as COPCs required a different approach than that used for the combustion by-products. Those compounds (PAHs, dioxin) benefit from consensus toxicity criteria (i.e., IRIS-established cancer Slope Factors) that allow for a quantitative screening paradigm. With the exception of asbestos, the building materials evaluated (including fibrous glass, crystalline silica, mica, portlandite, calcite and gypsum) do not have IRIS inhalation toxicity criteria from which to perform quantitative risk assessments. Complicating this matter is the knowledge that many of these substances were deposited in a large cloud from the collapse of the towers. Thus, the settled dust may serve as a reservoir for re­ suspension and eventual inhalation exposure. In addition, materials such as fibrous glass can also cause contact irritation when exposed directly to the skin.

The potential for exposure to building materials in the indoor environment was assessed by reviewing sampling data on the constituent composition of the indoor/outdoor bulk dust and indoor/ambient air [EPA, 2002c; USGS, 2001; NYCDOH, 2002; Chatfield «& Kominsky, 2001].

Toxicity criteria for building materials (with the exception of asbestos) were obtained from occupational sources, such as the Occupational Safety and Health Administration’s permissible exposure limits (OSHA PELs), and the American Conference of Governmental Industrial Hygienists threshold limit values (ACGIH TLVs). The evaluation of exposure potential coupled with toxicity information identified three COPCs (asbestos, fibrous glass and crystalline silica).

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