EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

upper boimd of 1 year) exposure duration. Note that contaminants (both non-carcinogens and carcinogens, alike) can exhibit acute effects from short-term, high-dose exposures. Because the Tier I benchmark levels are based on subchronic exposure (i.e., 1 year), acute effects from exposures that are below the benchmark levels would be unlikely. A review of EPA’s draft Acute Exposure Guideline Levels [EPA, 2001a] and California EPA’s (CAL-EPA) Acute Risk Levels demonstrates that the benchmark levels developed herein are categorically more stringent than the analogous US EPA and Cal-EPA acute levels.

Developing Risk-Based Criteria for Settled Dust

There is no established national guidance, and limited scientific literature, for assessing risk from interior surface wipe sampling (i.e., mass per unit area) data. The approach used in this report was adapted and modified from a methodology developed by the EPA Region III Superfund Program. It has been employed by the U.S. Anny Corps of Engineers to develop risk-based clean-up goals for interior surfaces at the Claremont Polychemical Superfund site in Region 11 [Radian, 1999]. Additionally, the methodology is similar to an approach employed by the NYSDOH for evaluating a dioxin contaminate office building P^SDOH, 1985] and one previously proposed by NJDEP for setting interior building surface clean-up goals [NJDEP, 1993].

A full discussion of the methodology employed for developing risk-based benchmarks based on contact with residues on indoor surfaces is presented in Appendix D. Briefly, this methodology provides an estimate of daily dose resulting from dermal absorption and ingestion associated with contacting contaminated surfaces and hand-to-mouth transfers. Dose is obtained by estimating the following: skin contact area and contact frequency with contaminated surfaces, transfer efficiency between surface and hand, transfer efficiency between hand and mouth, oral absoiption of the contaminant and dermal absorption of residual contamination on skin. Consistent with the approach for indoor air, toxicity criteria were obtained from IRIS. The assessment procedure is described briefly below and in more detail in Appendix D.

For the purpose of developing risk-based clearance levels for interior surfaces, this approach is preferable to an approach that relies on measuring contaminant concentration on a mass per mass (ppm) basis (as might be done for an exterior soil assessment). After cleaning has occurred, it would be difficult to obtain the mass of dust necessary to perform a mass per mass measurement of contaminant concentration. In addition, literature on interior lead contamination demonstrates a strong correlation between lead load (mass per unit area) and blood lead concentration in children (Lanphear et. al., 1998).

The following table lists the input parameters and numerical values (along with a brief explanation) used in this procedure. (See Appendix D for equations and a more detailed discussion.)

Table 3. Exposure parameters used to calculate clearance criteria for wipe samples.

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