WTC environmental health assessment draft, May 2002

NYC 9/11 Public Portal Document

For non-carcinogenic compounds, a resident’s daily intake of a contaminant is compared to the Reference Dose, which is the amount of a noncarcinogenic compound that someone may take in per day without adverse health effects. That comparison is called the Hazard Quotient (chronic daily intake/Reference Dose). According to EPA guidelines, if the Hazard Quotient (HQ) is greater than one, there may be concern for potential health effects. Therefore, for Tier DI, the no­ action-needed level, the benchmark was chosen for an Hazard Quotient (HQ ) of 1. For Tier I, the action level, an HQ Hazard Quotient of 10 is used, in accordance with the Hazard Evaluation Handbook. An HQ of 10 is used to account for the fact that chronic toxicity criteria (RfDs/RfCs) are being applied to sub-chronic exposure scenarios that are not expected to exceed six 6 months to one year in duration. Accordingly, an HQ Hazttrd-Qootierrt of 10 was used for non-carcinogens to reflect a similar (i.e., upper bound 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 benchmark levels are based on subchronic exposure (i.e., 1 year), acute effects from exposures that are below the benchmark levels would be unlikely. Additionally, a review of California EPA’s (CAL-EPA) Acute Risk Levels demonstrates that the benchmark levels developed are categorically more stringent than the Cal-EPA’s analogous acute levels.

Developing Risk-Based Criteria for Dust

Wipe sampling is a common technique used to estimate the amount of exposure that occurs from contact with contaminated surfaces. There is no established national guidance, and very little scientific literature, for the estimation of risks from wipe samples. The EPA approach used in this report was developed by the EPA Superfund program, and is consistent with evaluations found in literature. The approach involves analyzing the wipe sample for the concentration of the contaminant on the indoor surface, estimating the exposure to that contaminant concentration to determine dose in the body, and using this information to estimate risk.

Exposure to a contaminant on an indoor surface is estimated by calculating 1) the amount of the contaminant that is deposited on the skin touching the surface, 2) the fraction that is then transferred from the skin to the mouth, and 3) the fraction that is absorbed by the skin into the body. The three equations are as follows [Radian International 1999]:

1) Ds = CxSAxCFxFTSSxEFxED

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 (1/day) FTSS = Fraction transferred from surface to skin EF = Exposure frequency (days/year) ED = Exposure duration (years)

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CONFIDENTIAL, CITY_2IMCl00_003423792 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

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