Definition of toxicology and toxicity
Toxicology dates back to the earliest humans, who used animal venoms and plant extracts for hunting, warfare, and assassination. This science has been defined as the study of the adverse effects of chemical or physical agents on the individual living organisms. Modern toxicology goes beyond the study of the adverse effects of exogenous agents to the study of cellular, biochemical, and molecular associated mechanisms of action as well as functional effects and assesses the probability of their occurrence.
Definition of dose:
Total amount of a substance administered to, taken up, or absorbed by an organism, organ, or tissue.
Definition of exposure:
1. Concentration, amount or intensity of a particular physical or chemical agent or environmental agent that reaches the target population, organism, organ, tissue or cell, usually expressed in numerical terms of concentration, duration, and frequency (for chemical agents and micro-organisms) or intensity (for physical agents).
2. Process by which a substance becomes available for absorption by the target population, organism, organ, tissue or cell, by any route.
Toxicity can be defined as the inherent capacity of a chemical to cause adverse health effects. According to Paracelsus, everything has the potential to cause adverse health effects in sufficient quantities. The toxicity of a chemical depends on its dose - which is the amount of a chemical that enters in the body - and there is a range of possible effects, from subtle long-term chronic toxicity to immediate lethality. For toxicity to occur there has to be exposure - which is the contact of the outer boundary of an organism with a chemical. Some compounds can induce toxic effects directly while others require a conversion to a more bioactive form (e.g. in Europe, the acrylamide monomer is classified as "toxic" since it is highly reactive, whereas the polymer is not considered to be hazardous to health). Once occurred, chemical exposure can cause local effects (e.g. irritation and corrosivity at the site of contact) and/or systemic effects as a result of absorption into the bloodstream and distribution to the body (effects at different levels - cells, tissues and organs). Therefore, toxicity is a relative event that depends not only on the toxic properties of the chemical and the absorbed dose but also on the individual and interspecific variation in the metabolic processing of the chemical and the genomic make up of the organism. The first recognition of the relationship between the dose of a compound and the response elicited has been attributed to Paracelsus.
"All substances are poisons; there is none which is not a poison. The right dose differentiates poison from a remedy." Paracelsus (1493-1541).
