What is Toxicology?

Toxicology is the study of the adverse effects of chemicals on living systems, whether they be human, animal, plant or microbe. ‘Adverse effect’ can range from a life threatening injury to something that might be considered a minor annoyance. A mild irritant that causes watering of the eyes may not seem like a significant or real adverse effect, but for the person operating fine equipment, such effect can be not only deleterious but potentially dangerous.

Toxicology is an inter-disciplinary science that integrates the principles and methods of many fields: chemistry, biology, pharmacology, molecular biology, physiology and medicine. For example, by combining the study of the physiological effects of certain chemical structures and the molecular biological mechanisms that explain those effects, the toxicology can provide better understanding of the actions of a class of chemical substances, a finding of value to the chemist.

In the practice of toxicology other disciplines are also frequently relied upon. Hyrdogeologists, environmental engineers and air modelers are often used to determine the route, concentration and migration of chemicals in water, soil and air, respectively. Clinicians are relied on to record signs and symptoms and conduct differential diagnoses, to determine if a certain disease process is present and to eliminate other, non environmental causes.

The scientific pursuit of toxicology is typically divided between observational studies—looking at what effects result from exposure to a particular substance—and mechanistic studies, which attempt to understand and explain the basis for such effects. These two activities form the basis of toxicology as an experimental science, that is, that which takes place in the lab or occasionally in the field, as one usually thinks of science.

Risk assessment is another branch of toxicology which attempts to determine, probabilistically, outside the laboratory, the likelihood of an adverse effect based on a particular exposure scenario. This is not experimental activity, involves much more uncertainty about its findings and is as much art as science. It is conducted quantitatively, relying on mathematics and computer modeling, or qualitatively, relying more on experience and similar scenarios that have been previously looked at.

Regulatory toxicology relies on risk assessment and experimental data to determine the risk and benefits, or the costs and benefits of exposure to certain chemicals, to determine whether such chemical will be allowed in the public sphere and to what extent its use and exposure will be regulated. This field of toxicology probably has the greatest effect on our daily lives of all the different fields of toxicology.

Clinical toxicology involves the application of toxicological principles within a diagnostic setting, usually to determine whether a presenting adverse effect or disease or injury is due to some type of chemical exposure. This area of toxicology is typically practiced by a physician, nurse or other clinician, often times in consultation with the experimental toxicologist, who is in a position to better explain certain published experimental findings and whether they would be applicable to the case at hand.


Forensic toxicology focuses on medical-legal aspects of chemical exposure and toxic injury. Evaluation of analytical chemistry techniques and measurements, and testimony of conclusions and opinions in courts of law encompass the activity of this specialized field of toxicology.

The concept of dose is a basic principle in toxicology. The phrase, ‘dose makes the poison’ does capture a fundamental principle of toxicology, but the actual study of toxicology is much more nuanced and complex than this simple statement suggests.

Dose is the amount of chemical that comes into contact with the body or gets inside the body. Exposure is the amount of chemical in a media—air, water, soil or food—that is directly available to the body (through breathing, drinking, touching or consuming). Exposure includes both the concentration of the chemical in the media and the length of time such chemical is available to the body (concentration x time).

Although exposure is important in determining dose, other factors also come into play. For example, if two individuals are exposed to the same amount of chemical in the air—same concentration and for same length of time—one will inhale a much higher dose than the other if that person is exercising more vigorously. Even though exposure is identical for the two individuals, the faster and deeper breathing of the first individual will pull more chemical (i.e., dose) into the lungs.

Also, not all doses are equivalent in their toxicity even if they are equivalent in size. A high concentration of a chemical exposed for a short time can produce the same dose as a low concentration exposed for an extended period of time, but the effect of these equivalent doses may be quite different because of the concentrations of the chemical.

An acid, for example, requires a minimum concentration to exert a corrosive effect (that is, permanently damage tissue); below that threshold an acidic effect will not occur no matter how long exposure takes place (i.e., how large the total dose). So even though a low concentration of chemical for an extended period of time can produce the same dose as a high concentration for a short period of time, such effect will not be acidic (corrosive).

Dose does make the poison but so do other factors, such as concentration of the chemical and the threshold required to exert a particular effect. Important in the study of toxicology is understanding these different factors and how they intereact, and then determining which are of primary importance in each exposure scenario.


Thomas F. Schrager,Ph.D, Editor

About Cambridge Toxicology Group, Inc.


What is Toxicology?
By Thomas F. Schrager, Ph.D.

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