VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

5. Results and Discussion The exposure assumptions, the cancer risk estimates, and the incremental body burdens, are shown in Table 5. Before commenting on these results, it is important that they be put into perspective for general U.S. population dioxin TEQ exposures. As noted above, the background body burden of dioxin TEQs in adults is 18 ppt lipid. The draft Dioxin Reassessment estimates that the general adult population background TEQ exposure is 65 pg/day, or, expressed on a body-weight basis, 0.93 pg TEQ/kg-day. If this exposure is experienced over a lifetime, then the resulting incremental cancer risk fi-om background TEQ exposure to the general adult population is equal to about 1.4*10"’ (assuming the 1984 SF of 0.000156 [pg/kg-day] ’).

Table 5 shows that the TEQ ADD due only to inhalation during the period of exposure is 9 pg/kg-day for the WTC worker, 0.55 pg/kg-day for the office worker, and 0.73 pg/kg-day for the nearby resident. Although the WTC worker’s daily exposure is higher than that of the general U.S. population, it is experienced for only a small number of days. Therefore, when averaged over a lifetime, the WTC worker dose calculates to an incremental cancer risk that is 3*10"®, which is about 2 orders of magnitude lower (100 times lower) than the U.S. background cancer risk from dioxin-like compounds (1.4*10"’ as calculated above). The office worker and resident experience incremental lifetime cancer risk at about 3*10'’, three orders of magnitude lower (1000 times lower) than backgroimd. EPA regulatory programs, such as the Superfund Program, typically consider individual incremental cancer risk estimates made in this manner (i.e., in the context of a scenario-based risk assessment) in the range of 10"* to 10^ to be of potential significance, depending on the circumstances. Exposure to dioxin-like compounds represents a unique circumstance, in that background exposures are already within this range and, in fact, at the upper end of this range. Therefore, although the upper bound incremental cancer risk to the WTC worker is estimated to be within the range of 10"* to 10"®, EPA judges these incremental cancer risks to be of minimal concern because they are 100 times and more lower than typical background exposures to dioxin-like compounds.

For noncancer risk, an increment of body burden, IBB, approach has been used. Table 5 shows that the exposure of the WTC worker suggests that his or her body burden could rise up to 10% above current average background, but that the nearby office worker and the residents have a rise of only 1% or less. EPA judges these incremental body burden increases to be of low significance, given the relatively high backgroimd exposures already experienced by the general population.

A key uncertainty remains as to the inhalation exposures that could be experienced by WTC rescue or clean-up workers, or nearby resident and office workers, who were in the area during the time period from about December onward. As discussed earlier, most of the samples had non-detects, but after assuming that the concentrations in the air were one-half the detection limit, all the measurements in 2002 from the EPA ERT samplers, which included the WTC Building 5 monitor, the Church & Dey monitor and many others, ranged from about 0.5 to 5.0 pg TEQ/m’, which is about 5 to 50 times higher than normal background air concentrations. The three Region 2/7 samplers, the Park Row, Chambers St, and the Albany & West samplers, reported concentrations near 0.05 pg TEQ/m’ from around December, 2001, through their last reported measurements in March, 2002. These were further away or generally upwind from the WTC site, so it cannot be assumed that they represent concentrations to which WTC workers and

DRAFT-DO NOT QUOTE OR CITE 81 October 2002

NYC-VVTC_000149025