IGNOU MZO 007 2026 - Explain the concepts of dose, threshold dose, and LD50 in toxicology.

Question

Explain the concepts of dose, threshold dose, and LD50 in toxicology. Differentiate between acute and chronic effects of toxicants with appropriate examples.

29 Jan 2026

Answer :

Word Count : 472

In toxicology, the concept of dose refers to the amount of a substance or toxicant administered or absorbed by an organism, usually expressed in terms of mass of substance per unit body weight, such as milligrams per kilogram (mg/kg). The dose determines the biological response, as even essential substances can become harmful if consumed in excessive amounts. Toxicologists study dose-response relationships to understand how varying levels of exposure influence physiological effects. The threshold dose is the minimum dose of a toxicant that produces a detectable effect on an organism. Below this dose, no adverse effects are observed, indicating the organism’s capacity to tolerate or detoxify low levels of the substance. For instance, certain vitamins like vitamin A have beneficial effects at low doses, but only above the threshold dose do toxic effects such as liver damage or teratogenicity appear. Threshold doses are crucial in establishing safety limits and regulatory standards for chemicals in the environment, food, and drugs. LD50, or lethal dose 50%, represents the

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