Exposure Assessment

Because thousands of industrial and commercial chemicals are in use today and distributed globally, many of which pose a potential health risk to organisms and the environment, exposure assessment is a critically important process. Exposure assessment is a method of measuring or estimating an organism's level of exposure to a toxic compound or group of compounds. Exposure is usually defined as the amount of a chemical in the environment that may affect an organism. In the recent past, exposure assessment has become an integral part of green enterprises because of their interest in environmental sustainability. Additionally, exposure assessment is a major component of the risk assessment process to prevent liability for the use (and, perhaps, misuse) of toxic chemicals. Exposure assessment also integrates information about observed and reported adverse health effects in organisms and communities. As such, exposure assessment is key to the maintenance of a safe workplace.

The risk assessment process, originally formalized by the National Academy of Sciences’ paradigm in 1983, has four components: hazard identification, dose response evaluation, exposure assessment, and risk characterization. Exposure assessment is central to this risk analysis process and asks questions like “What are the types and levels of exposure, as well as what are the pathways of exposure and bioavailability of the toxin?” In other words, exposure assessment is the process of measuring or estimating toxic chemical concentrations, duration, frequency of exposure, and pathways to an organism that arise from chemicals released into the environment. For example, a company that is introducing a new type of carpet glue would conduct such an analysis to make sure that the product does not contain levels of toxins that could later harm people who are exposed to them in homes or workplaces.

Clearly, in these assessments, first examined is the element of exposure to a toxin, which is the process by which a chemical becomes available for intake and/or absorption by individuals in a population. The concentration of the chemicals is a vital consideration in this assessment. It requires a calculation of how much toxin reaches an identified target [Page 251](be it a specific population, animal, plant, organ, or cell). This calculation is expressed in quantitative terms for various scenarios that include contingencies for different pathways or durations of exposure.

Although exposure differs from the related concept of dose—in that exposure is the quantity of a chemical in the environment that is in contact with an organism while the dose refers to the level of the chemical actually absorbed by the individual—both exposure and dose are usually reported in exposure assessments. Exposure levels depend on a number of physical factors such as volatility, partition coefficient, molecular weight, polarity, and related concerns. Types of exposure range from deliberate (food additives) to accidental (industrial accidents that release toxic chemicals) to incidental (mercury via the environment). To perform an exposure assessment, the properties of the chemical, such as water solubility, the ability to migrate through the soil, or the ability to bind to airborne particulate matter, are characterized to identify potential routes to the target. Possible exposure pathways include the routes by which a contaminant reaches an individual via inhalation, ingestion, or dermal contact.

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