Toxicology

Toxicology is the scientific study of poisons (or toxins). Major topics in toxicology include the detection and chemical analysis of poisons, the study of the metabolic effects of these substances on organisms, and the investigation of methods for treatment of poisoning.

The Swiss physician and alchemist Philippus Aureolus, also known as Paracelsus (1493-1541) and said to be the father of the modern science of toxicology, wrote "All things are poison, and nothing is without poison, the dose alone makes a thing not a poison." In other words, if poisoning is to be caused, an exposure to a potentially toxic chemical must result in a dose that exceeds a physiologically determined threshold of tolerance. Smaller exposures do not cause poisoning.

Physiology is the study how organisms function, and the disruption of biochemical pathways by poisons is a key aspect of toxicology. Poisons affect normal physiology in many ways, but some of the more common mechanisms involve the disabling of enzyme systems, induction of cancers, interference with the regulation of blood chemistry, and disruption of genetic processes.

Organisms vary greatly in their tolerance of exposure to chemicals, and even within populations of the same species there can be great variations in sensitivity. In rare cases, some individuals may be extremely sensitive to particular chemicals or groups of similar chemicals, a phenomenon known as hypersensitivity.

Organisms are often exposed to a wide variety of potentially toxic chemicals through medicine, food, water, and the atmosphere. Humans are exposed to complex mixtures of chemicals, many of which are synthetic and have been either deliberately or accidentally released into the environment.

In some cases, people actively expose themselves to chemicals that are known to be toxic, such as when smoking cigarettes, drinking alcohol, or taking recreational drugs. Voluntary exposure to chemicals also occurs when people take medicines to deal with illness, or when they choose to work in an occupation that involves routinely dealing with dangerous chemicals. However, most exposures to potentially toxic chemicals are inadvertent, and involve living in an environment that is contaminated with small concentrations of pollutants, for example, those associated with pesticide residues in food, lead from gasoline combustion, or sulfur dioxide and ozone in the urban atmosphere.

Traditionally, the discipline of toxicology has only dealt with the direct effects of poisonous chemicals on organisms, and particularly on humans. Recently, however, ecologists have broadened the scope of toxicological investigations to include the indirect effects of chemicals in the environment, a field known as ecotoxicology. Ecotoxicology could be defined as the study of the ecological effects of toxic chemicals, including the direct effects, but also the indirect consequences caused by changes in the structure of habitats, or in the abundance of food. A herbicide used in forestry may not cause direct, toxic effects to animals at the doses given during the pesticide application, but the pesticide may change the vegetation, and thereby change the ecological conditions upon which animals depend.