Toxicology

Toxicology

The study of the adverse effects of chemicals and physical agents on people, animals, and other living organisms. It is a science that studies the harmful effects of drugs, environmental contaminants, and naturally occurring substances found in food, water, air, and soil.

Toxicologist

A scientist who studies the harmful effects of chemicals and assesses the probability of such harm.

Toxin

Refers to toxic substances (usually proteins) that are produced by biological systems such as plants, animals, fungi, or bacteria.

Toxicant

Used when discussing toxic substances that are produced by or are a by-product of human activities.

Toxicology Risk Assessment

A process involving: 1. Hazard identification—associated harms. 2. Dose-response assessment—attempt to quantify. 3. Exposure assessment—considering route of exposure. 4. Risk characterization—assesses the probability of harm to human and other populations.

Hazard Identification

Identifying the associated harms of a substance. This involves looking at sources of toxicological data such as structure-activity analyses, in vitro tests, in vivo animal studies, and human studies.

Dose-Response Assessment

An attempt to quantify the relationship between the dose of a substance and the resulting effect.

Exposure Assessment

Considering the route of exposure to a substance. Common routes include oral/ingestion, inhalation, dermal, and injection.

Risk Characterization

Assessing the probability of harm to human and other populations based on hazard, dose-response, and exposure assessments.

Acute Exposure

Exposure for less than 24 hours, usually refers to a single administration.

Subacute Exposure

Repeated exposure for 1 month or less.

Subchronic Exposure

Repeated exposure for 1 to 3 months.

Chronic Exposure

Repeated exposure for more than 3 months.

Graded Dose-Response Curve

Relates the dose to the intensity of the effect; the y-axis is the degree of response.

Quantal Dose-Response Curve

Relates the dose to the frequency of the effect; the y-axis is the frequency of response, often used in toxicology when looking at populations.

ED50

The dose that is effective in 50% of the population.

Emax

The maximum effect achievable with a drug or toxicant.

LD50

The dose that is lethal (or toxic for TD50) in 50% of the population.

TD50

The dose that causes a defined toxic effect in 50% of the population.

Therapeutic Index (TI)

Compares the dose that is therapeutic with the dose that causes toxicity and gives a numerical indication of the relative safety of a drug. It is calculated as LD50/ED50. A wide therapeutic window or a high therapeutic index is best.

Margin of Safety

Also known as the Certain Safety Factor (CSF), calculated as LD1/ED99.

LD1

The dose that is lethal (or toxic for TD1) in 1% of the population.

ED99

The dose that is effective in 99% of the population.

Variability in Toxicity

Differences in how individuals or populations respond to toxic substances, influenced by factors such as dose, duration, frequency of exposure, route/site of administration, age, size, sex, diet/nutrition, disease state, genetic variability, environmental modifiers, and repair mechanisms.