WTC environmental investigation report, Sep 2002

NYC 9/11 Public Portal Document

Final Technical Report of the Public Health Investigation Page 56 of 56 t There are many uncertainties about whether this risk would be realized. The first is that even though the risk of cancer is not linear, the risk estimates treat it as linear (36). Therefore there may be an overestimate of risk at low exposures compared with the studied populations. The air levels of silica we are examining here are well below those studied in worker populations; therefore even this small increased risk may be overestimated. Conversely, the studied populations were adult workers. So risk estimates based on these studies may underestimate risks to children and to adults with respiratory disorders.

Less soluble materials have a longer residence time in the lung and therefore have a greater potential to contribute to tissue damage or malignant disease. Within SVF types, glass fibers and slag wool are considered the most soluble, and therefore least toxic. Mineral wool is less soluble than glass wool. Fibers longer than approximately 15 microns, the diameter of a macrophage, are also cleared less efficiently, leading to a greater potential for adverse effects (26).

t Early studies often relied upon injection and implantation studies, which may not accurately predict a pulmonary response from inhalation exposures. A review of inhalation studies indicates that glass wool did not cause pulmonary fibrosis or lung cancer in these animal studies (47). A recent study by Hesterberg indicates no increase in pulmonary fibrosis or lung cancer even at doses of 222 f/cc, although cancer incidence in control animals was considered high (51).

This slope factor is based on epidemiologic studies and assumes a linear dose response for cancer, even at very low environmental doses (0.23 excess cancers per million people exposed for each f/cc of asbestos.) This type of cancer risk estimate may over predict risk and does not take into account any lower threshold for effect, which may exist. Additionally, the EPA slope factor was designed to apply equally to all types of asbestos, and all fibers greater than 5 microns in length (IRIS).

+ Variability in these factors is not accounted for in the EPA slope factor because it does not include synergistic effects with the effects of smoking (48).

t However, because asbestos as a percentage of settled surface dust was elevated, an area with significant dust may be capable of generating higher airborne levels of asbestos, especially during high activity.

http://www.atsdr.cdc.gOv/asbestos/lowennanhattan/ResSamp_Sep2002_Text.html 07/18/2003 NYC-WTC_000178443