VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

site, where elevated exposure rates limited to a period of days or months contributed to a pool of dioxin already accumulated in the human body over a lifetime. The current estimated body burden of dioxin (including only the 17 dioxin and furan congeners, not the dioxin-like PCB congeners discussed above) in U.S. adults is approximately 18 pg TEQ per gram of body lipid (18 ppt TEQ lipid). This average was derived from data on older as well as younger adults. Because exposures were known to be higher in the past, the body burdens of younger adults will be lower than those of older adults. Another factor contributing to the variability seen in the entire population is dietary pattern; individuals whose diets are higher in animal fat will have higher body burdens.

The effects of dioxin in humans range from biochemical changes at or near background levels to potentially adverse effects of increasing severity as body burdens increase above background levels. The “margin of exposure”, MOE, can be defined as the ratio of body burden where effects are foimd divided by a body burden at a level of interest. The MOE for dioxin at current average body burdens (i.e., current average body burdens being the level of interest) is considerably less than that typically seen for environmental contaminants of toxicological concern. The potential contribution to health risks from specific dioxin sources or specific exposures, such as exposures from inhalation of air with elevated levels of dioxin, is best evaluated through calculating the incremental contribution of this source to the body burden.

The draft Dioxin Reassessment has assumed that a one-compartment, first-order pharmacokinetic (PK) model can be used to estimate the body burden that results from a specific intake regime. This simple PK model and its application to dioxin TEQs is also described in Lorber (2002). For an exposure of a finite time, the nonsteady-state form of this model to predict an increment in body burden (IBB) from a constant intake dose is given by:

IBB = [ADD/(k * LW)] * [1 - e’’“] (5)

where IBB is the increment of body burden on a lipid basis (pg/g, or ppt, lipid basis); ADD is the average daily dose (pg TEQ/day; not on a body weight basis), k is the first-order dissipation rate constant (1/day), LW is the weight of body lipids (g; equal to full body weight times 0.25, as described above), and t is the time of exposure (days). Use of Equation (5) with an average ADD over the period of exposure will provide an estimate of body burden at the end of the exposure. This is the time when the incremental body burden will be at its largest. In the scenarios of this assessment, different daily exposures result from different air concentrations as well as differences in exposure - 5-day work week followed by 2 days of non-exposure for the office worker scenario. Equation (5) is applied on a daily time step using Excel® spreadsheet procedures for this simple screening exercise.

A value of 17,500 g for the lipid weight (calculated as: 70 kg * 0.25 lipid fraction * 1000 g/kg), and a k of 0.000267 day' ( = 0.098 yr ', corresponding to a 7.1 year half-life) will be used (Lorber, 2002). Results for this exercise include both an incremental body burden estimate, the IBB of Equation (5), calculated at the end of the exposure period, as well as a percent increase over background this represents. This percent increase is calculated as, [IBB/BK] * 100%. The BK is the background, which was assigned a value of 18 ppt TEQ lipid, as described above.

DRAFT-DO NOT QUOTE OR CITE 80 October 2002

NYC-WTC_000149024