VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

Section IV. Evaluation

A uniform approach to characterizing the impacts of all pollutants is not possible because the available background data and screening benchmarks vary between compounds. Similarly, the relevance of these data for the circumstances of exposure following the WTC disaster also varies with the type of contaminant being evaluated. When benchmarks are available for the circumstances at hand they provide a quantifiable approach for assessing the impact of human exposure. Such benchmarks are used and described, as appropriate.

Background or pre-existing levels of environmental contaminants provide an important reference point for describing the environmental impact of the destruction of the WTC. If the monitored levels for a pollutant after the disaster did not appreciably exceed values commonly found in New York or other urban settings, concerns about elevated health risks will be reduced. On the other hand, when contaminant levels are in excess of background, a careful evaluation of the potential health impacts is warranted. Exceedence of background levels does not itself necessarily imply that potential health risks exist. Also, for some pollutants, background measurements might at times show substantial levels and have associated health risks. Thus, comparisons with background levels need to be interpreted in light of the health risk data for the pollutants.

As discussed below, air concentrations and subsequent exposures after September 11 were generally elevated for each pollutant over a limited span of time. Measured concentrations for most air pollutants were reduced by the beginning of 2002. Many of the environmental health criteria have been developed to address “chronic” exposures to contaminants that are present in the environment for years or decades. Exposure levels that exceed a chronic health reference level for a limited period would generally be less likely to result in adverse health effects. Where available, this report has tried to use acute and sub-chronic screening standards. When chronic screening standards are used, the relevance of the comparison is discussed.

In this report, reference is made to OSHA health criteria for the protection of worker’s health. These criteria are valuable for the analysis of WTC data for several reasons. Criteria exist for many compounds, not all of which have established environmental health criteria, and they address risks due to less than lifetime exposures. However, there are limitations in applying occupational criteria to evaluations of environmental health risks. Occupational criteria serve to protect relatively healthy worker populations that would typically be less diverse than the general population (in terms of age and health status). Occupational criteria also apply for workday periods, with exposures ceasing during nonworking hours; environmental exposures are typically more continuous. Finally, risk levels that have been accepted in occupational settings may exceed those accepted for long-term environmental exposures to the general population. For these reasons, EPA has not generally used occupational standards as a basis for environmental health criteria.

It is important to reiterate that very limited data are available on the levels of exposure that occurred to individuals due to direct contact with the plume of smoke and dust generated by the WTC collapse on September 11. Such exposures would have been of limited duration, but levels of contaminants may have been significantly higher than those measured in monitoring

DRAFT-DO NOT QUOTE OR CITE 23 October 2002

NYC-WTC_000149104