Toxicology

Abstract Toxicology is the study of interactions between chemicals and biological systems. Toxicology attempts to identify the adverse effects chemicals might induce in humans and the dose‐response relationships that would allow one to predict the relative safety/risk of a chemical exposure. Toxicological investigations attempt to define the nature of the harmful effect; severity of the effect as a function of exposure or dose; mechanism(s) causing the effects; detection, recognition, and quantitation of toxic effects; and reversibility of adverse effects. Toxic effects may be classified as local or systemic; and as latent, persistent, cumulative, or transient. They can include inflammation, necrosis, immunosuppression, neoplasia, mutagenesis, neurotoxicity, enzyme inhibition, teratogenesis, as well as others. Factors influencing toxicity include number, magnitude, and routes of exposures; and time of dosing, as well as formulation and impurities of materials. Routes of exposure include ingestion, through the skin (dermal), and inhalation, or multiple routes may be involved. The site of absorption, the metabolism of the toxic agent in organs like the liver and kidney, and the distribution of the agent and its metabolites to different tissues are all toxicokinetic features that may impact the toxicity of the chemical. Dose‐response relationships are useful in determining causality, range of sensitivity in a population and hence of hazard, assessment of no‐ or minimum‐effects doses. Dose‐response comparisons across species are helpful in predicting the possible range of human sensitivity when human data are unavailable. Dose–response comparisons across chemicals are useful for defining potency differences that may be used to select the best chemical available for a specific application. Toxicology testing procedures may be general or specific, and many guidelines must be followed. General studies monitor body weight, hematology, chemical pathology, and organ weight, among others; and types of studies include acute toxicity studies, short‐term repeated studies, and chronic and subchronic toxicity studies. Examples of specific studies include primary irritancy and immune‐mediated hypersensitivity studies, and neurological and behavioral toxicology. Review of studies and the relevance of toxicology in hazard evaluation are briefly examined. An introduction to the risk assessment process and its use of toxicity data is provided.