Mixed Routes of Exposure

Abstract

While many human exposures to chemicals are by multiple exposure routes, one route usually predominates and there may be a tendency to think of the predominant route as the only route of concern. In environmental exposures a toxic material may be in the air, on food and/or in drinking water. Dermal exposure is possible if contaminated water is used for bathing. Inhalation exposure is also possible if the toxic material is volatile in hot water. The route of exposure(s) is a factor both in the design of toxicity studies and in the evaluation of a chemical's effect in humans. When testing a chemical for toxicity in animals, the route of primary concern should be the route of exposure(s) during human use. A whole-body exposure or a nose-only exposure might be used to judge the effect of pulmonary exposure. Whole-body inhalation will result in test material being deposited on the fur of experimental animals. Dermal and oral exposure, as a result of grooming, may result in a significant exposure under these conditions. The length of exposure period, short time, such as intravenous (instantaneous) or oral (bolus), compared with longer exposures such as in drinking water, inhalation exposure over a six hour period per day or continuous dermal exposure, may also be important for the response if multiple routes of exposure are of concern. A workplace exposure could result in both inhalation and dermal exposure. Absorption and metabolism most likely will proceed at different rates, and this possibly could affect the course and nature of the toxic response. Many regulatory agencies and industries rely on risk assessment in making risk management decisions. Risk assessments usually examine several routes of exposure, independently, and then the different routes of exposures are added together to define the total exposure and risk. Many times very conservative default assumptions are used. Keywords: nose-only; whole body; group versus individual housing; grooming; occupational exposure; environmental exposure; biological markers; risk assessment