WTC environmental investigation report, Sep 2002

NYC 9/11 Public Portal Document

Final Technical Report of the Public Health Investigation Page 27 of 56 were alkaline (pH of 8.6 and 9.8). On the pH scale of 0 (acidic) to 14 (alkaline or basic), these values are slightly alkaline. Mineral analysis of these two settled surface dust samples estimate levels of calcite (15%J, 19%J) and portlandite (6%J, 3%J) were present, respectively. These crystalline minerals along with other components of concrete would have contributed to the measured alkalinity.

C. Air

The settled surface dust results discussed previously indicate the materials present in each area sampled. Fibers and small particles within the dust may become airborne during daily activity or during periods of high activity such as cleaning. Therefore, the settled surface dust sample results are an indicator for areas with a potential for airborne contaminants. Air sampling was conducted to determine the actual levels of fibers, dust, and crystalline minerals in the air at the time of settled surface dust sampling. Where feasible, these results are correlated to the settled surface dust results.

1. Fibers in Air

Samples for airborne fibers were first analyzed by phase contrast microscopy (PCM) to count all fibers present according to the National Institute for Occupational Safety and Health (NIOSH) Method 7400 counting rules. Phase contrast microscopy identifies fibers based on size and shape, but not the specific type of fiber. Therefore, the fibers seen by PCM include asbestos fibers as well as other fibers, such as textiles, fiberglass, and cellulose that might be present. Any sample with airborne fibers above the highest PCM levels found in the comparison locations was re­ analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The TEM methodology can distinguish what types of fibers are in a sample, particularly asbestos fibers. The SEM method identifies SVF. Some fibers present in the settled dust of the area may become suspended in the air and be present in the air sample.

a. Indoor Air

Fiber levels in air are expressed as the number of fibers in each cubic centimeter (cc) of air or fibers per cc (f/cc). Low levels of fibers were found in the comparison areas above 59th Street homes, where fiber levels ranged from less than 0.001 f/cc (<0.001 f/cc) to 0.003 f/cc. Because no asbestos was detected in the settled surface dust of the comparison areas above 59th Street, these fibers are not likely to have been asbestos. SEM analysis showed they were not SVF. Figure 7 shows all airborne fiber levels determined by PCM in the lower Manhattan area with respect to the fiber levels found in the comparison areas above 59th Street. These data represent all fibers found according to the analytical method used (NIOSH 7400) and are not specific to asbestos or SVF.

The majority of the lower Manhattan air samples from indoor areas without asbestos in the dust were within the range of fibers found in the comparison areas above 59th Street (<0.001 to

http://www.atsdr.cdc.gOv/asbestos/lowermanhattan/ResSamp_Sep2002_Text.html 07/18/2003 NYC-WTC_000178414