Law Department notice on WTC document preservation, Oct 2001

NYC 9/11 Public Portal Document

assessing WTC ambient data.) Since this was done very quickly during an emergency situation, these benchmarks were not subjected to peer review.

In addition to not knowing the health impacts of certain individual pollutants, information was not available on the cumulative or synergistic impacts of being exposed to several pollutants at once. For example, one medical expert suggested there may be a synergistic effect between PAHs and asbestos, since PAHs resemble cigarette tar. Studies have shown the lung cancer risk from exposure to asbestos is increased exponentially for cigarette smokers. In addition, this expert noted that the combination of high pH and the small shards of glass found in WTC dust could have had a synergistic impact on the acute respiratory symptoms that many people experienced.

There were limitations with all three methods used to analyze asbestos concentrations in the ambient air and bulk dust in Lower Manhattan. These limitations, which were not noted in EPA’s press releases, restricted EPA’s ability to make definitive assessments about the health risks posed by asbestos. However, even with these limitations, sufficient data existed to identify the presence of asbestos in the dust and ambient air, and to warrant that persons working around the dust take necessary precautions to not inhale the dust. The three methods used and their limitations follow:

• Transmission Electron Microscopy (TEM) is a sensitive method generally used to analyze air samples collected from a relatively clean indoor environment. At the WTC site, many samples could not be analyzed because the filters being used to collect asbestos were overloaded with particulates. For example, 24 of the 69 samples collected as of September 17 could not be analyzed because the filters were overloaded. • Phase Contrast Microscopy (PCM), which was used to analyze asbestos concentrations in ambient air beginning September 18, can only Count fibers in the filter greater than 5 micrometers in length. A study at the WTC site found that the majority of the asbestos fibers at the site were less than 5 micrometers in length. • Polarized Light Microscopy (PLM) was used to measure asbestos in bulk dust. This method is primarily an estimation method that is not very precise, and has a detection limit of 1 percent. Therefore, using this method against a strict benchmark is not reliable.

According to EPA, essentially all outdoor areas at the WTC site were vacuumed, and the detection methods did not impact the action actually taken to remove the dust from outdoor areas. See Appendix E for a summary of EPA’s outdoor air asbestos sampling results.

13 Report No. 2003-P-00012

NYC-WTC_000145368