EPA interim final report on WTC background study, April 2003

NYC 9/11 Public Portal Document

Input Parameter Value Explanation SA (Skin Surface Area) 400 cm^ Palm Side of Hands CF (Contact Frequency) 16/day See Appendix D FTSS (Fraction Transferred from 0.05 See Appendix D Surface to Skin) EF (Exposure Frequency) 365 days/yr Days in Residence [EPA, 1989] ED (Exposure Duration) 30 years Upper-bound Estimate of Time in Residence [EPA, 1989] ABSo (Oral Absorption Fraction) 1 See Appendix D FTSM (Fraction Transferred from 0.1 See Appendix D Skin to Mouth) ABSd (Dermal Absorption Fraction) 0.03 (dioxin) Chemical Specific [EPA, 2001b] 0.13 (PAHs) BW (Body Weight) 70 kg Average Adult [EPA, 1989] AT-NC (Averaging Time - Non Carcinogen) AT-C (Averaging Time - 25,550 days See Appendix D Carcinogen) CSF (Cancer slope factor -dermal 1.0 E+6 (dioxin) Dioxin Reassessment: EPA, 2001 and oral) 7.3 E 0 (PAHs) HUS, 2002

In light of the limited data for many of the input parameters used to estimate dose from exposure to residues on surfaces, conservative exposure estimates were employed. Still, there may be a concern for highly exposed sub-populations. Infants and young children constitute such a group due to age-specific activities such as crawling and mouthing and increased surface-area to body­ weight ratios. In cases where non-carcinogenic effects are driving clearance levels, the difference in dose on a mg/kg/day basis between an adult and a young child could be considerable. However, in this document the two compoimds (dioxin, PAHs) for which the surface contact methodology has been used to develop clearance levels are carcinogens, so it is this effect that drives the clearance levels. As such, the Tier HI clearance level is strongly influenced by overall exposure duration, which in this assessment has been set at 30 years. Consequently, weighted over 30 years, the impact of a high-exposure period (i.e., early childhood) is diluted. It is acknowledged that Tier I (one year exposure duration) screening levels for carcinogens may luiderestimate cancer risk for children, but Tier I contaminant levels are not expected to persist, therefore the magnitude of any associated uncertainty would be small. If a contaminant was to be added to the COPC list that had its clearance level based on a non­

15

NYC-WTC_000145972