EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

Residues on Indoor Surfaces The most formal EPA guidance which addresses this issue is the “Standard Operating Procedures (SOPs) for Residential Exposure Assessment” originally published by the Office of Pesticides in 1997 and updated in 2001 (EPA, 1997a and EPA, 2001a). This guidance was designed for estimating exposures to pesticides. Pesticides are typically applied to indoor surfaces as liquid or sprayed formulations which would create surface residues which are likely to be somewhat different than the fine dust particles associated with the WTC attack. So while this guidance was considered, a number of other sources were also reviewed including the Superfimd guidance on dermal contact (EPA, 1989), the procedures used to develop re-entry guidelines for the Binghamton State Office Building (Kim and Hawley, 1985), procedures used by NJDEP for setting interior building surface clean-up goals (NJDEP, 1993), the building clean-up procedures presented by Michaud et al (1994) and an approach developed by the EPA Region III Superfund program that has been employed by the U.S. Army Corps of Engineers to develop risk-based clean-up goals for interior surfaces at the Claremont Polychemical Superfimd site in Region n (Radian, 1999). Elements from these various methods were combined to derive the procedure shown below. The procedures involves 3 steps: 1) estimating the amount of chemical deposited on the skin using skin area, contact frequency and transfer efficiencies, 2) estimating the dermal dose based on an absorption fraction and 3) estimating the ingestion dose based on the fraction of material on hands that is transferred to the mouth.

1. Estimating Amount of Chemical Deposited on Skin

Ds = C X SA X CF X FTSS x EF x ED

Ds = Amount of chemical deposited on skin (mg) C = Concentration of chemical on contaminated surface (mg/cm^) SA = Exposed skin surface area (cm^) CF = Contact frequency of skin against surface (l/day) FTSS = Fraction transferred from surface to skin EF Exposure frequency (days/year) ED Exposure duration (years)

2. Estimating Dermal Dose

Dd = (Ds X (1 - FTSM) x ABSd) / (BW x AT)

Dd Dermal dose (mg/kg/day) BW= Body weight (kilograms) FTSM = Fraction transferred from skin to mouth AT = Averaging time (days) ABSd = Dermal absorption fraction

3. Estimating Oral Dose

Do = (Ds X FTSM x ABSo) / (BW x AT)

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