Risks & Choices,
Center for Chemistry Education, Miami University (Ohio)
www.terrificscience.org—Permission granted to copy for classroom use only.
An Introduction to Toxicology
Toxicology is the science of poisons (also called toxins). It deals with the chemical nature of
poisonous substances and how they produce adverse effects in biological systems. A poison
is generally defined as any chemical agent that has the capacity to produce abnormal,
undesirable, or harmful changes to an organism exposed to it. Poisoning by a chemical
agent is equivalent to chemically induced disease. In humans, adverse effects of poisons
can range from minor symptoms like headache and nausea to severe ones like convulsions
and coma. The ultimate adverse effect is death.
The toxicity of a chemical is an inherent property of the chemical. It cannot be changed
without changing the chemical to another form. Most toxins work by altering basic cellular
metabolic functions in ways that disrupt normal physiological processes. They are also the
target of biochemical reactions in the body that render them inactive (detoxification).
Toxicology is a complex, interdisciplinary subject, straddling the fields of chemistry, biology,
pharmacology, medicine, genetics, economics, and law. Contemporary toxicology is usually
divided into three main branches:
clinical toxicology, which deals with the effects of toxins (typically in the form of drugs)
on human patients;
forensic toxicology, which is concerned with detecting the criminal use of toxic agents;
environmental toxicology, which studies the effects of industrial and agricultural
toxins on human health and the environment.
Regulatory toxicology, with its emphasis on public policy/risk assessment, and occupational
toxicology, which concerns toxic exposure in the workplace, are also sometimes considered
separate branches of toxicology.
While the subject of toxicology can be quite complex, a basic understanding of its
fundamental principles is important if citizens are to make learned decisions about the risks
and choices inherent to environmental health issues.
The Fundamental Principle of Toxicology
Early humans recognized basically two types of substances—beneficial ones (water, food,
and medicine) and harmful ones (poisons). However, more recent science has shown that
virtually every substance is toxic, although the quantity or dose needed to cause specific
effects varies considerably. Paracelsus (1493–1541) stated this idea nearly five centuries
ago: “All substances are poisons; there is none that is not a poison. The right dose