Organs may be more sensitive to certain poisons because of the way the poison is distributed in the body or because of the way the organ reacts with, responds to, or metabolizes the poison. Mechanism of action includes the biochemical, physiologic, and anatomic changes caused by a toxicant that result in its characteristic toxic effects. The latter allows comparisons of expected activity on animals or people of different size. For gases or vapors, dose is estimated as a product of the concentration of the poison in air multiplied by the number of minutes the person breathed the contaminated air. If a person is breathing a constant volume of air each minute, then the amount of poison taken into the lungs can be doubled by either doubling the time in the same environment or by doubling the concentration with the same time.
Temporal characteristics refer to how long the exposure continued.
Acute exposures are usually a single dose or a single period lasting from a few seconds to as long as a day or so. It is determined by exposing or dosing small groups of animals to different amounts of poison, noting the number in each group that die, and determining a dose that would kill half of them. Nature of exposure refers to such questions as whether the chemical is pure or in a mixture, the route by which the poison enters the body, and the physical and chemical state of the toxicant. Receptor characteristics include individual susceptibility based on age, gender, or genetic make-up. Children, for example, may be more susceptible to lung irritants than adults owing to their small, easily-obstructed airways.