Development of an exposure assessment method for epidemiological studies of New York State personnel who responded to the World Trade Center disaster.

Objectives: An exposure assessment method was developed for use in assigning an exposure score to New York State personnel who responded to the World Trade Center disaster site after the 11 September 2001 terrorist attacks.

Methods: The method consists of an algorithm with two instantiations. Each represents a major component of the overall exposures at the site: dust and smoke. The algorithm uses US Environmental Protection Agency air monitoring data collected between 23 September 2001 and 28 February 2002, as well as information on duration, location and time period of work assignment and type and frequency of personal protective respiratory equipment (PPE) use, collected by a self-administered mailed questionnaire. These data were used to calculate an overall exposure score for each participant. For each time period/location combination, individuals provided average number of hours and number of days worked. This was multiplied by a weighting factor derived from the median of the air monitoring data for the time period/location. Calcium was chosen as a surrogate for the dust exposure, so the weighting factors for the dust instantiation were calculated from calcium air monitoring data. Total hepta-chlorinated dibenzo-p-dioxin was chosen as a surrogate for the smoke exposure and was similarly used in the smoke instantiation.

Results: More individuals in the highest exposure score category performed tasks such as search/rescue and hand digging than those in the lowest exposure category. Also, those in the highest exposure category had a higher mean number of hours at the site than other exposure groups.

Conclusions: The exposure assessment method presented accounts for PPE use, amount of time at the site, proximity to the site and ambient air monitoring results taken in the immediate vicinity. The algorithm can be used to rank individuals in the same study with very different patterns of exposure, such as high-level, short-term exposures and low-level, long-term exposures. The concepts could be modified for use in other epidemiological studies where long-term chronic exposure is a concern.