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. (A) 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 LD50
(median lethal dose) or LC50 (median lethal concentration) or
EC50 (median effective concentration).

6. Objectives of acute toxicity test -
1. To predict hazard to non-target species
2. To assess toxicity in target species.
3. To provide information on the mechanism of toxic
action.
4. 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 –
1) To assess the nature of the toxic effects.
1) 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 –
1) To study adverse effects of chemicals on the structure
and function of organs, tissues and cells after prolonged
period of exposure.
2) To study secondary effects of toxicants such as
carcinogenicity.
3) To evaluate safe levels of toxicants.

9. EXPERIMENTAL DESIGN FOR TOXICITY
TESTS
1) 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
2) ROUTE OF ADMINISTRATION –
The toxicant should be administered through the route by which
they’re exposed.
3) 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