NYC-WTC_000232959

NYC 9/11 Public Portal Document

7, Asbestos

Asbestos refers to a group of natural fibrous silicate minerals of various structures (18). Used primarily for its fire resistant properties and as an insulation material during the 1900s, asbestos is now known to cause pulmonary damage, lung cancer, and mesothelioma. Asbestos fibers less than 2 microns in diameter and less than 5 microns in length with a 3:1 aspect ratio may enter and deposit in the alveolar and pleural regions of the lung (10). Material that is not cleared by the normal processes of the lung will remain, resulting in possible damaged tissue, fibrotic lesions, and cancer (10,52-54). Fibers may also migrate from the lung to the pleural lining, causing mesothelioma. This discussion will focus on the most studied health effects, asbestosis and cancer. It should be noted that the chrysotile asbestos found in settled surface dust during this investigation is believed to be cleared from lungs to a greater degree than other forms of asbestos (10). Therefore the following review, which considers all forms of asbestos, would be conservative for chrysotile asbestos exposures.

a. Asbestosis

Asbestosis is similar to other mineral pneumoconiosis of the lung. Fibers are deposited in the lung and remain due to their insoluble nature and the inability of lung macrophages to engulf and remove longer fibers (>5 microns in length) (10,54). These fibers can create localized tissue damage, stimulate the immune system, and create a scarring of the lung.

Asbestosis has been observed in workers exposed over several years to levels much higher than seen environmentally. It is believed the cumulative exposure to asbestos correlates to the development of asbestosis, and some cases of asbestosis have been reported with only a brief high exposure documented (55). Because cumulative asbestos exposure is believed to be the appropriate metric for assessing asbestos health effects, it is possible long-term, continuous low-level exposures could contribute to asbestosis. Recent studies of a population exposed to tremolite asbestos in Libby, Montana, do indicate increased pleural anomalies, consistent with asbestosis, for individuals who were not exposed occupationally. Individuals who lived with plant workers or those who had contact with vermiculite piles containing tremolite had increased odds ratios for these anomalies (56).

Although asbestos is present in some settled surface dust in lower Manhattan, aggressive sampling produced a maximum level of 0.003 f/cc (PCM). This level is not high enough to result in asbestosis after short exposures. Although it is theoretically possible that lower level environmental exposures could contribute to disease over extended exposures, the data from this pilot study are too limited to support that finding.

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