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. Understanding toxicology requires recognition of the spectrum of toxic effects. In the U.S., the FDA requires an extensive process to determine drug efficacy and safety before marketing is permitted. Hence, the probability of adverse effects from use of these agents is very small. Therefore, the probability of adverse effects from sufficiently high exposures tends to be much greater.