Exposure is a necessary but not sufficient condition for toxicity. This may seem trivial, but we have been astonished how often educated people overlook the fact. Before an illness can result from poisoning, enough of the poison must be absorbed into the body to cause harm. They can, however, escape those containers through a variety of mishaps and move through air, water, soil, or food to where a person is. Analysis of how poisons move from where they were created to where a person could be poisoned by them will be discussed in the article on exposure and risk assessment.
Toxic response is a function of the characteristics of the toxicant and of the exposure.
Characteristics of toxicants that alter the response include the source, chemical form, and physical state of the toxicant. Arsenic provides an example of variation in toxicity with source and also with chemical form. Generally, toxicologists consider elemental arsenic to be much more potent than methylated arsenic in terms of causing cancer or neurotoxicity. Physical state refers to whether the toxicant is in the form of a solid, liquid, or gas or vapor. An example of the influence of physical state on toxicity obtains from considering how vaporization of a liquid solvent increases likelihood of inhalation, rapid absorption into the body, and rapid onset of acute toxic effects.