Exposure assessment is an evaluation of the potential exposures to humans and the environment from the production, distribution, use, disposal and recycle of a chemical substance. Exposure assessment is just as important as hazard identification in determining risk from a chemical substance, because risk is a function of both hazard and exposure.

Often, in the absence of measured exposure information, computer models are used to help estimate various exposure scenarios from product use, ranging from worst case to most likely. These models use information on the chemical’s properties and assume various use patterns to generate estimated exposure information that helps complete the risk assessment process.

There are four considerations in any exposure assessment:

• Likelihood of exposure
• Magnitude of exposure
• Route of exposure
• Population exposed

Likelihood of exposure refers to the probability that contact between the substance and a human or environmental receptor will occur, given the product application. To determine likelihood, it is important to identify the potential ways in which contact may occur and the routes of exposure — ingestion, inhalation or dermal.

Magnitude of exposure refers to the level, or dose, of exposure. In addition to assessing the amount (volume or concentration) of exposure, it is also important to determine the duration, or length of time, of exposure.

Routes of exposure include inhalation, ingestion and skin absorption. Inhalation is often the most common route followed by skin absorption and ingestion.

Exposure assessment is not complete without identifying the population exposed. Exposure can generally be grouped into three categories: workplace exposure, consumer use, and environmentally-mediated exposure.¹

Workplace Exposure
Workplace exposure includes exposure in occupational environments where the chemical substance is manufactured, formulated, and used commercially. In these settings the chemical substance is usually in concentrated form, and the workers may be directly involved in handling it.

Industrial hygienists, trained professionals who evaluate exposure in workplaces, take into consideration the following in their assessments:

• Characteristics of the facility to identify locations where exposure is most likely to occur
• How the chemical substance is handled — in open systems, where the worker may have greater potential for contact, or closed systems, where the production vessels are sealed and exposure potential is reduced or eliminated
• Population of exposed workers
• Work assignments of exposed workers
• Physical properties of the chemical substance, to help identify what route of exposure is most important
• Properties of the chemical substance, such as odor or irritation that might serve as a warning of unsuspected exposure and help to limit exposure
• Quantitative measures of exposure (amounts, duration), and occupational exposure limits
• Potential for accidental exposure
• Engineering controls designed to isolate workers from exposure
• Behavioral controls, such as the use of personal protective equipment, designed to protect workers from inhaling or ingesting a chemical substance, or from dermal contact with the material

Consumer Use
Exposure assessment for consumer use of a product is similar to that for workplace exposure. However, the information is often more difficult to obtain and there is greater potential for accidents or product misuse that might result in unexpected exposures.

Environmentally-mediated Exposures
Environmentally-mediated exposures result from a product finding its way into food, water, or air supplies. Estimating exposures from these sources requires knowledge of the environmental fate of the substance and information on human intake. Alternatively, direct measurement of concentrations in air, water or food may be made.²

Additional information on exposure assessment can be found at Alliance for Chemical Awareness.