Types of toxicity

Toxicology is the branch of science that deals with nature, effects, and detection of poison. The degree to which a substance can harm an organism is called toxicity. The types of toxicity depending upon the time of exposure of the toxicant have been described.

1. Acute Sub-acute and Chronic Toxicity Rajshree Jha Master of Science Life Sciences Semester-II

2. INTRODUCTION Toxicology is a Greek word that means “ the science of poison”. In other words, The branch of pharmacology which deals with the various aspects of poisons and poisoning is known as toxicology. Poison may be defined as a substance which, even in small dose, produces adverse effect in the metabolism of an organism and consequently may cause death. Du Bois and Geiling (1959) defined toxicology as a branch of medical science that deals with the nature, properties, effects and the detection of poison.

3. TOXICITY TEST Toxicity test are experiments or trials designed to assess or evaluate the doses/concentration of toxicants and the duration of exposure required to produce a criterion effect. Types of toxicity tests – The toxicity tests may be conducted at various levels .

4. Test types based on number and conditions of species 1) Single species test 2) Multispecies test 3) Ecosystem test (B) Test types based on exposure of toxicants 1) Single dose test 2) Multiple dose test (C) Test types based on length of exposure 1) Acute toxicity 2) Sub-acute toxicity 3) Chronic toxicity

5. ACUTE TOXICITY TEST Acute in toxicology relates to exposure on one occasion only (i.e. single exposure). It is sometimes acceptable for multiple exposure during a short period of time. Acute toxicity may be cited as severe effects experienced by organisms during short term (24-96 hours) exposure to toxicants. The results are generally represented in terms of LD 50 (median lethal dose) or LC 50 (median lethal concentration) or EC 50 (median effective concentration).

6. Objectives of acute toxicity test - To predict hazard to non-target species To assess toxicity in target species. To provide information on the mechanism of toxic action. To observe the behavioural responses of the experimental toxicology.

7. SUB-ACUTE TOXICITY It is also known as short term toxicity. This study involves a stimulus and produces a response in longer time and may become chronic. This study involves repeated administrations, usually on a daily or five times per week basis. Objectives of sub-acute toxicity tests – To assess the nature of the toxic effects. Human beings are often exposed to chemicals at much lower levels but over a longer period of time.

8. CHRONIC TOXICITY TEST It involves repeated administrations over a considerable period of the lifespan of the test animals. Also known as long term but definite toxicity. Objectives of chronic toxicity test – To study adverse effects of chemicals on the structure and function of organs, tissues and cells after prolonged period of exposure. To study secondary effects of toxicants such as carcinogenicity. To evaluate safe levels of toxicants.

9. EXPERIMENTAL DESIGN FOR TOXICITY TESTS SELECTION OF ANIMAL SPECIES - Choice of test species for predictive toxicity testing is often affected by economic consideration, limitation of laboratory facilities or by problems associated with real target species . Rattus norvegicus Mus musculus Two rodents species are most often used for the study, the laboratory rat and the laboratory mouse.

10. Many species of birds are vulnerable to intoxication by pesticides. eg. Starlings, Pigeons, Mallards, Domestic fowl etc. Fish may also be exposed to pesticides. eg. Brown trout, common guppy, mosquito fish etc. Mallard Brown trout ROUTE OF ADMINISTRATION – The toxicant should be administered through the route by which they’re exposed. DOSAGE – ‘Dose’ is defined as the quantity of toxicant received by the animal at one time or in a given period of time. Dosage refers to the administration of a toxicant in doses.

11. 4) OBSERVATION AND EXAMINATIONS – After administering the toxicant they should be examined not only for the number and time of death. The examination should also be done for central, autonomic and behavioural effects. Autopsy and post mortem examinations are done to detect histological abnormalities.

12. SIGNIFICANCE The essence of toxicity testing is not just to check how safe a test substance is but to characterize the possible toxic effects it can produce. The use of animal in toxicity testing is most likely to continue for ht foreseeable future because of the benefits they offer in examining a whole functioning organism.

13. Reference - FUNDAMENTALS OF TOXICOLOGY Dr. Kamleshwar Pandey Dr. J.P. Shukla Dr. S.P. Trivedi