VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

concentration from September 19 to October 12 was assumed to be 8.4 pg/m’, the measurement on October 12 at the Park Row monitor, and the TWA concentration between September 19 and November 30 was 4.8 pg TEQ/m\ The rate of inhalation for an office worker was assumed to be the average inhalation rate of 1.0 m’/hr, which is defined as “light activity” in EPA’s Exposure Factors Handbook (EPA. 1997).

31 Resident: This individual was exposed 24 hours per day, 7 days per week, and the exposure began on September 19 and ended on November 30. As with the office worker scenario, the assumption here again was that individuals living near Ground Zero, in the vicinity of the Park Row monitor, were more exposed after September 19, when some of the locations outside of Ground Zero opened up to workers and residents. The daily inhalation rate was 0.55 m^/hr, an average daily rate, activity unspecified, as developed in EPA’s Exposure Factors Handbook (EPA, 1997). As noted, the air monitor used to characterize the air concentration was the Park Row monitor, which was located in an area not restricted after September 19. The average TEQ concentration during this time was 4.8 pg/m\ as noted above.

3. Procedurefor Cancer Risk Estimation These assumptions and the resulting ADDs are shown in Table 5. Cancer risk were estimated simply as:

LADD = ADD * [ED/LT] (4a)

Risk =LADD*SF (4b)

where LADD is the lifetime daily dose (pg TEQ/kg-day), Risk is the upper bound incremental excess lifetime cancer risk that results from the exposure described by LADD, ADD is the average daily dose during the period of exposure (pg TEQ/kg-day), ED is the exposure duration (days), and LT is lifetime (days), typically 70 years, and SF is the upper boimd cancer slope factor, expressed in inverse units to LADD, or [pg TEQ/kg-day]‘‘. The SF of .000156 [p^g- day]"' was developed by EPA in 1984 for 2,3,7,8-TCDD exposures (EPA, 1984). It is applied to TEQ exposures in this cancer risk screening exercise. The draft Dioxin Reassessment (EPA, 2000) proposed an SF of 0.001 [pg/kg-day] ', which applies to dioxin TEQ exposures.

4. Procedurefor Non-Cancer Risk Estimation For noncancer risk, a different approach was taken. The best indicator of exposure for persistent, bioaccumulative, toxic substances such as dioxin is the concentration of the chemical in the organ or tissue of concern. A common metric for dioxin exposure is the “body burden”, which is defined as the concentration of dioxins in the body, typically on a whole-weight basis. Body burden in this screening assessment is expressed on a lipid basis. It is assumed that adults are 25% lipid by weight, so that a lipid-based concentration can easily be converted to a whole­ weight-based concentration by multiplying by 0.25.

Dioxins build up and decline over prolonged periods of time, since the overall biological half-life (the time for half the chemical to dissipate by either biological degradation or elimination) of dioxins in the human body is approximately 7 years. The use of the body burden as the measure of dose has implications for short-term exposures, such as those near the WTC

DRAFT-DO NOT QUOTE OR CITE 79 October 2002

NYC-WTC_000149023