WTC environmental investigation report, Sep 2002

NYC 9/11 Public Portal Document

Final Technical Report of the Public Health Investigation Page 8 of 56 determine if, on the basis of its composition, it could be an irritant if it became airborne or came in contact with skin or eyes during cleaning activities.

The dust samples were analyzed for the presence of asbestos and SVF using polarized light microscopy (PLM). PLM can distinguish between fiber types by their unique appearance and color when viewed under different wavelengths of light. In addition, TEM analysis was conducted on all dust samples that showed asbestos content by PLM as less than 1%. TEM analysis is very specific, can detect smaller fibers of asbestos, and is subject to less interference than PLM.

The dust samples were also analyzed for mineral content using XRD as described previously for the air samples. For the dust samples, the mineral and the fiber results are expressed as a percent, indicating the weight percent each component represents in the portion of the dust sample analyzed. The different analytical techniques, XRD and microscopy (PLM, TEM, SEM), help to characterize what was in the settled surface dust; however the results from the two methods each performed on a portion of the dust collected, cannot simply be added together to "sum up" what was in the dust. XRD results are based upon the weight of the dust sample analyzed. While, PLM, TEM, and SEM results are based on the surface area viewed under the microscope.

Limitations While the goal of the sampling was to evaluate the air and dust samples for a range of contaminants, there is no one sample collection method or analysis that can provide all of the determinations that were desired. The analysis strategy was to identify what components were present in order to provide the public with information quickly if any of the analyses revealed a significant concern. In order to strive for both of those goals, some modifications to conventional protocols were made which limited some analyses from determining the precise level of the materials in the sample (e.g., XRD conducted on air and dust samples). Whenever an analysis is expanded beyond its specific intent, there is the potential loss of sensitivity and an increase in the variability in the data. Those particular analytical results are reported as estimated values and marked with a "J."

Results for the airborne particulate matter were rejected due to issues found during the quality assurance analysis. However, the XRD analysis for airborne minerals that used the same filter samples as the particulate matter analysis are considered valid because the analysis method does not depend on the filter sample weighing process used to determine the particulate matter concentration. The XRD mineral air concentrations are based on individual mineral weight standard curves—not the weight of the dust sample collected on the filters. These standard curves are not impacted by pre- and post-sampling filter weight variability.

http ://www.atsdr.cdc.gov/asbestos/lowermanhattan/ResSamp_Sep2002_T ext.html 07/18/2003 NYC-WTC_000178395