Exposure assessment elements and methodologies

Exposure Assessment: Approximating Rates of Exposure

For the purposes of an exposure assessment, a point of contact of exposure is defined as the exposure of an individual to an outside agent, at a specific concentration of the agent, over a particular interval of time (t-e) upon contact of the barrier of the individual's body and the environment (Prezant et. al. 2002). Lung, skin, and gastrointestinal exposure must all be subjected to analysis -- exposure can occur through multiple pathways. However, according to Prezant (et al. 2002), when conducting an exposure assessment of a particular area, such as the remains of the World Trade Towers, it is not always desirable or possible to directly measure the concentration of the substance in question at the moment of contact with the individual in question.

Point-of-contact measurements, after the fact, can provide a reasonable approximation of exposure, particularly if accompanied with time-activity pattern data from existing case studies or simulations. The scenario, the duration, the individuals involved, frequency, and intensity of the exposure must all be taken into consideration. And even under the best of circumstances, some guesswork is always required as "an investigator often does not have data for all aspects of the exposure assessment and the available data may be of questionable or unknown quality" (Prezant 2002).

Data gaps must also be acknowledged, and approximated if at all possible. When approximating, conservative estimates should be made -- in other words, when assessing an individual's exposure to second-hand smoke, assuming exposure over a 24-hour period (the maximum possible exposure to the environment) rather than the minimum, is usually preferred. or, in the case of childhood exposure to lead paint, even if this cannot be confirmed, if the individual lived in an area where residency in lead-painted accommodations was likely, exposure to the toxin may need to be factored into an analysis of the subject's health status. Conservative estimates seem like a necessary, compassionate, allowance assessing the complications caused by 9/11. 9/11 was an extraordinary, unprecedented event, and data collection at the point of time was virtually impossible, yet it had very real effects upon emergency responders, given their higher rate of manifesting respiratory illnesses. Creating an approximation of exposure seems necessary for both ethical as well as environmental reasons, to ensure these responders are compensated for long-term, job-related health consequences.