WTC environmental investigation report, Sep 2002

NYC 9/11 Public Portal Document

Final Technical Report of the Public Health Investigation Page 24 of 56 Manhattan.

All settled surface dust samples were analyzed by polarized light microscopy (PLM) for fiber type and content. This technique distinguishes between asbestos fibers, textile fibers, and synthetic vitreous fibers (SVF), which include glass wool and mineral wool. The results are reported as a percent. Because PLM is an optical method, the amount reported is a visual estimation of the percent of area viewed. Therefore it is neither strictly a weight or a volume percent. These results do provide an indication of the presence of asbestos or SVF in the dust, and some idea of relative amount.

In lower Manhattan, asbestos was only detected in settled surface dust in one indoor and two outdoor locations by PLM (Figure 8). If asbestos was not seen in the sample or reported as <1% by PLM, a second test was done which is more sensitive, transmission electron microscopy (TEM). An additional 4 outdoor and 15 indoor locations contained asbestos when examined by TEM (Figure 9). Chrysotile asbestos was the only form of asbestos identified, either by PLM or TEM, in all settled surface dust samples. In this study TEM is primarily used as an indicator of the presence or absence of asbestos. For the PLM analysis, values <1% are an indicator of the presence of asbestos because this is the detection limit for PLM. For TEM a detection of asbestos is confirmation of its presence. Therefore, values <1% and values greater indicate the presence of asbestos. Results shown in Table 6 and discussed below refer to all samples positive for asbestos, by either the PLM or TEM methods (Figure 10).

Asbestos was found in indoor settled surface dust in 10 of 57 residences sampled in lower Manhattan (18%) (Table 6). The settled surface dust in common areas contained asbestos in 5 of 26 areas sampled (19%), and asbestos was found in outdoor dust in 6 of 14 areas sampled (43%) (Table 6). Asbestos levels ranged from none detected up to 3.4% (the highest level was found in an outside sample). However, without surface-loading information, the percentage of asbestos present does not allow for characterization of potential exposures. No asbestos was found in the comparison homes north of 59th Street. Figure 10 depicts the results of analysis of the asbestos content of settled surface dust in samples from residences in lower Manhattan.

The SVF results, seen in Table 6, show a broad range of SVF content in the settled surface dust from none detected up to 35% in indoor dust samples and as high as 72% outdoors. The location and range of SVF found in settled surface dust is shown in Figure 11 for all areas sampled in lower Manhattan. SVF was found in indoor dust in 26 of 57 residences sampled as analyzed by PLM (46%). The settled surface dust in common areas contained SVF in 14 of 26 areas sampled (54%), and SVF was found in outdoor dust 11 of 14 times sampled (79%). The majority of SVF detected was glass wool. Only four buildings contained mineral wool in settled surface dust, ranging from l%-7%. Because no surface­ loading information is known, the exact percentage is less informative than its presence. No SVF was found in the comparison homes north of 59th Street by PLM analysis. Therefore the SVF content of settled surface dust in some areas of

http://www.atsdr.cdc.gOv/asbestos/lowermanhattan/ResSamp_Sep2002_Text.html 07/18/2003 NYC-WTC_000178411