TOXICOLOGIC TERMS & DEFINITIONS
Hazard is the ability of a chemical agent to cause injury in a given situation or setting; the conditions of use and exposure are pri-mary considerations. To assess hazard, one needs to have know-ledge about both the inherent toxicity of the substance and the amounts to which individuals are liable to be exposed. Humans may be able to use potentially toxic substances when the necessary conditions minimizing absorption are established and respected. However, hazard is often a description based on subjective esti-mates rather than objective evaluation.Risk is defined as the expected frequency of the occurrence of an undesirable effect arising from exposure to a chemical or physical agent. Estimation of risk makes use of dose-response data and extrapolation from the observed relationships to the expected responses at doses occurring in actual exposure situations. The quality and suitability of the biologic data used in such estimates are major limiting factors.
The route of entry for chemicals into the body differs in different exposure situations. In the industrial setting, inhalation is the major route of entry. The transdermal route is also quite impor-tant, but oral ingestion is a relatively minor route. Consequently, primary prevention should be designed to reduce or eliminate absorption by inhalation or by topical contact. Atmospheric pol-lutants gain entry by inhalation and by dermal contact. Water and soil pollutants are absorbed through inhalation, ingestion, and dermal contact.
Toxic reactions may differ qualitatively depending on the duration of the exposure. A single exposure—or multiple exposures occur-ring over a brief period from seconds to 1 or 2 days—represents acute exposure. Multiple exposures continuing over a longer period of time represent chronic exposure. In the occupational setting, both acute (eg, accidental discharge) and chronic (eg, repetitive handling of a chemical) exposures occur. Exposures to chemicals found in the environment such as air and water pollut-ants often cause chronic exposure, but sudden large chemical releases may result in acute massive population exposure with seri-ous or lethal consequences.