EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

of professional judgment; such exposure would obviously involve a very physical job with frequent contact with the walls and floor. The value recommended here is 16 contacts per day and is based on professional judgement. If available, site-specific activity data should take precedence.

Fraction Transferred from Surface to Skin fFTSSI This will vary depending on type of surface, type of residual, hand condition, force of contact, etc. Rodes et al. 2001 conducted experiments on particle transfer to dry skin and measured transfers of 10% from carpets and 50% from hard surfaces. These transfer efficiencies were found to decline with repeated contacts. The OPP guidance recommends 5% of application rate for caipets and 10 % for hard surfaces (EPA, 1997a). USEPA has previously assumed transfer of 0.5 for PCBs (EPA, 1987) based on an Office of Toxic Substances (OTS) assessment. Michaud et al (1994) assumed 0.5 for PCBs and dioxins, but stated that 0.1 might be more realistic. In developing re-entry guidelines for the Binghamton State Office Building after a fire, a 100% transfer was assumed (Kim and Hawley, 1985). In a study of Malathion uptake from different surfaces, USEPA-EMSL found that FTSS of malathion from painted sheetrock to human hands was only 0.0003. (Mean transfer from vinyl flooring to hands was 0.0018, and from carpet to hands was 0.0152.) Malathion is a pesticide assumed tO have lipophilicity more similar to PCBs than to volatiles or metals. However, the representativeness of such a number for PCBs and dioxins is unknown. PCBs are more lipophilic (have higher Kows) than malathion. A value of 5% is recommended here. Although this is on the low end of the literature values, when combined with the high contact frequency, it provides a fairly high total transfer to skin.

Exposure Frequency (EFl A value of 365 days/year is used to represent a full time resident.

Exposure Duration (EDI A value of 30 years is assumed to match upper bound estimate of time in a residence (EPA, 1997b).

Fraction Transferred from Skin to Mouth (FTSMl Michaud et al (1994) assumed that all of the residues deposited on the fingertips would be transferred to the mouth, twice per day. A similar approach is used in the OPP guidelines. In the Binghamton re-entry guideline derivation, a range of factors were used; 0.05,0.1, and 0.25 representing the fraction of residue on hand that is transferred to the mouth (Kim and Hawley, 1985). A similar value of 10% is recommended here.

Oral Absorption Fraction (ABSOl For chemicals whose dose-response parameters are based on experiments in which the absorption fraction is similar to the one expected in the exposure scenario, there is no need to adjust the RfD orCSF.

Body Weight (BWl A value of 70 kilograms is assumed which represents an average adult (EPA, 1997b).

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