In understanding potential health effects of chemicals, exposure describes the measurement of both the amount of, and the frequency with which a substance comes into contact with a person or the environment.
Exposure refers to the amount of a particular chemical that reaches an organism, ecological system, or group of people, expressed in terms of physical state, concentration, duration and frequency. Exposure is a critical determinant of the probability of human harm (i.e., risk) actually resulting from a particular chemical.
It is a fundamental tenant of toxicology that “the dose makes the poison,” meaning that a trace exposure to a specific substance may have no effect, but a 1,000-fold or 10,000-fold exposure has the potential to cause harm. Tests designed to assess exposure can be highly sensitive and provide data on specific effects; address the most sensitive developmental life stages; be predictive across species, sex, and age; and be relevant to assess potential human health and ecological effects of exposure.
Merely being in the presence of a chemical does not necessarily equate to exposure, as a chemical can be inert in a particular material or the trace amount present in a product may not present any risk. In some industrial settings, the chemical may be contained inside a closed system, or controls such as ventilation may be in place. Also, the use of personal protective equipment, such as a respirator or gloves, can often prevent exposure altogether or greatly reduce the potential for exposure.
“Exposure Assessment” is the process of measuring or estimating the intensity, frequency and duration of human exposures to an agent currently present in the environment, or of estimating hypothetical exposures that might arise from the release of chemicals into the environment.
Exposure assessments include environmental measurements (levels in air, water, soil, food, etc.) and physiological measurements (levels in blood, urine and tissue samples), both of which provide essential information for wildlife, epidemiological and experimental studies.
Exposure assessments can provide an accurate representation of the dose received by an individual. Although an individual may be exposed to a certain concentration of an agent, many factors will determine the effective concentration of the agent that organs, tissues and cells are actually exposed to. In addition, a chemical agent must persist in the environment long enough to interact with an organism for any exposure to actually occur. Moreover, the biochemical properties of the agent (water solubility, sensitivity to heat, light) will determine the lifespan of a chemical substance in the environment following its release.