WTC health criteria appendix, Dec 2001

NYC 9/11 Public Portal Document

AT =Averaging time (days)

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

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

Several assumptions are incorporated into these equations. They assume that volatilization of the chemical on the surface is negligible, and that the chemical is available on the surface for the entire exposure duration (that is, that a previous transfer of contaminant from surface to skin would not deplete the amount of surface contamination). It is assumed that there is a "maximum Ds"; that is, that there would be a limit on how much contaminant could be transferred to the skin in a single day, but that maximum Ds is unknown. Therefore, this method tends to be conservatively biased with respect to oral and dermal exposure. If inhalation exposure is to be considered, the volatilized amount should be subtracted before estimating the amount available for dermal transfer.

Although these equations are limited by the above assumptions, they are basically sound in theory. The difficulty is in defining the specific inputs to the equations, since some of the input parameters have very little or no experimentally determined values in the literature. Previous assessments have usually relied upon professional judgment.

For that reason, it was felt that the multiple risk-based level approach, based on the range of possible inputs, was appropriate. RME assumptions were selected, along with "low-end" and "worst-case" values, in an attempt to bound the estimated RME risks.

Concentration of Chemical on Surface (C)

This is the parameter that was be derived for each scenario, and is compared with the site data.

Exposed Skin Surface Area (SA)

Skin surface areas have been well-defined in the experimental literature. The Exposure Factors handbook is a good source. For adult workers, some percentage of the total surface area is usually appropriate. The use of protective gear by industrial and maintenance workers, such as masks and gloves, is possible, but it depends upon the specific type of work and is a case-by- case decision.

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CONFIDENTIAL, CITY_21MC100_003423737 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176149