1 physicochemical properties including the functional groups, (ii) solubility in water and organic solvents, (iii) dose/concentration, (iv) ionic characteristics (v) translocation and biotransformation, (vi) their mode of action, and (vii) interaction with other chemicals. Almost all these characteristics are dependent on the structure of compound. 2 Toxicity of chemicals is greatly affected by various factors pertaining to their exposures to the organisms. 3 The factors of surrounding medium affecting the toxicity of chemicals have been extensively worked out for the aquatic medium. The factors related to the medium are physico- chemical characteristics of the water affecting the toxicity of chemicals 4 the factors related to the organisms are very important in the study of toxicity of xenobiotics.

1. Factors influencing toxicity-
Environmental, Genetic, Nutritional
Narendra Kr. Maurya
Jr. MFSc
College Of Fisheries Mangalore

2. CONCEPT OF TOXICITY
 Toxicity is the degree to which a substance can damage
an organism.
 Toxicity can refer to the effect on a whole organism, such as
an animal, bacterium or plant, as well as the effect on a substructure
of the organism, such as a cell (cytotoxicity) or an organ such as
the liver (hepatotoxicity).

3. Characterizing Toxicity
1. Acute Toxicity, which is the amount of a toxicant that will cause an
adverse effect within a relatively short period of time (e.g., from
instantaneous to within a few days).
2. Chronic Toxicity, which is the long-term response to a toxicant.
Although the same types of dose–response curves are used to
measure the chronic toxicity of toxicants

4. Toxicity can also be characterized by the type of adverse response they
create.
 Carcinogens cause cancer, either by the initiation or promotion of an
uncontrolled growth of cells.
 Mutagens cause mutations by altering the DNA sequences of
chromosomes.
 Teratogens cause mutations in the DNA structure of developing
fetuses that can result in developmental abnormalities.

5. What is the Environmental toxicology
 Environmental toxicology is the multidisciplinary study of the effect
of manmade and natural chemical on health and the environment
 This includes the study of the effects of chemicals on organisms in
their natural environments and in the ecosystem to which they belong
The simplest definition found to date is that ecotoxicology is "the
study of the harmful effects of chemicals upon ecosystems"

6. There are three main objectives in ecotoxicology
 Obtaining data for risk assessment and environmental management.
 Meeting the legal requirements for the development and release of
new chemicals into the environment.
 Developing empirical or theoretical principles to improve
knowledge of the behaviour and effects of chemicals in living
systems.

7. GENETIC TOXICOLOGY
 Genetic toxicology, by definition, is the study of how chemical or
physical agents affect the intricate process of heredity.
 Genotoxic chemicals are defined as compounds that are capable of
modifying the hereditary material of living cells.
 In higher organisms, hereditary information is organized in
chromosomes.

8. NUTRITIONAL TOXICOLOGY
 Nutritional toxicology deals with substances found in food that might
be harmful to those who consume sufficient quantities of the food
containing such substances.
 Such substances can be inherent toxicants, substances naturally found
in foods, or contaminants, which are substances that find their way
into food either during the preparation or processing of such foods.
 Nutritional toxicology is the study of the nutritional aspects of
toxicology.

9. Cont.…
 Nutritional toxicology is related to and might even overlap but is not
synonymous with food toxicology.
 Nutritional toxicology emphasizes toxicants or toxins found in
foods, whereas nutritional toxicology targets the interrelations that
toxicants or toxins have with nutrients in the diet, which affect
nutritional status.

10. FACTORS AFFECTING TOXICITY
Characteristics which affect the toxicity of a chemical are considered as modifying factors.
For the sake of convenience, this will be divided into following four sections:
 1. Factors pertaining to chemical,
 2. Factors pertaining to exposure,
 3. Factors pertaining to surrounding medium, and
 4. Factors pertaining to organisms.

11. 1. Factors pertaining to chemical
 (i) Chemical composition
 (ii) Dose or concentration of chemical
 (iii) Translocation of toxicant
 (iv) Biotransformation of toxicants

12.  Decrease toxicity (antagonism)
 Add to toxicity (additivity)
 Increase toxicity (synergism or
potentiation)
 (v) Chemical interactions

13. 2.Factors pertaining to exposure
 Exposure routes
 Exposure duration
 Exposure systems
 Absorption
Toxicity of chemicals is greatly affected by various factors pertaining
to their exposures to the organisms.

14. 3. Factors pertaining to the surrounding
medium
The factors of surrounding medium affecting the toxicity of chemicals
have been extensively worked out for the aquatic medium.
 Water temperature
 Dissolved Oxygen
 pH
 Salinity
 Water hardness
 Suspended and dissolved matter

15. 4. Factors pertaining to organisms
Toxicity of chemicals is evaluated against a particular organism or a
group of organisms.
 Species
 Sex
 Age
 Life-stage

16. Cont.….
 Size
 Health and nutrition
 Acclimation
 Metabolism There are two types of metabolism:
Detoxification
Bioactivation
 Excretion
 Distribution Within the Body