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Lecture

Week 10 Lecture


Department
Environmental Science
Course Code
EESA10H3
Professor
Jovan Stefanovic

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Toxicology
Toxicology
Definition:
Study of poisons
the science which studies toxic substances or poisons, that are substances which cause alteration or
perturbation in the function of an organisms leading to harmful effects (Truhaut, 1974)
Poisons are compounds and cause negative impacts on human health
Subject of research in toxicology: from the sources of these poisons, the composition, the
partition in the environment, exposure (how someone gets exposed to this), from which
source, how much (dose), what kind of response human body can have, chemistry of the
poison
Toxicology: assessing chemical hazards (1)
How harmful a substance is depends on:
Chemical properties of the substance
Electronegativity
Polarity – water is polar (has negative and positive side), all chemicals that are polar
dissolve well in water
While non-chemicals are not dissolvable in water
Relates polarity to solubility
Polar chemicals mostly stay between the cells in human tissues, they are not
able to penetrate through the cell walls because they have fats (non-polar)
While the non-polar chemicals are soluble in fats, they are able to go through
the cell wall and enter the cell
Oxidation state
Molecular weight
Dissociation
Solubility
Water soluble toxins
Fat soluble toxins
Toxicology: assessing chemical hazards (2)
Persistence of chemical (i.e. DDTwe want to have a prolong effect of DDT to protect the crops, but
from an environmental perspective, persistence is not something we prefer/like)
Bioaccumulation = chemicals accumulate in particular tissues in the human body (muscles, brain, hair)
Biomagnification = building up the level of the chemical in the food chain (i.e. animals at the top of the
food chain are the highest to have the highest level of chemicals in their bodies)
Chemical interaction (chemicals are always exposed to more than one chemical at the same time,
interaction can reduce or increase toxicity)
Antagonistic = when one chemical reduces the toxicity of another one
Some vitamins (A and E) may reduce human reaction to some carcinogens
Synergistic = when two chemicals are together, one of them become more toxic
E.g. smoking in the presence of asbestos
Multiple chemicalsfood additives, pesticides, air pollution
Receptor
Dose
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Response
Toxicology: Receptor (i.e. human being or any animal or plant, anything)
1. Receptororganism receiving exposure or dose
Frequency of exposure
Age
General health – chronic disease, heart disease, asthma that may increase the vulnerability of the person
Genetic makeup – maybe one person will be more susceptible while others are not
Toxicology: Dose
2. Dosethe amount of substance a person has:
Ingested (often greatest source of chemical exposure, 85%)
Inhaled (air pollution, particles and volatiles, 10%)
Absorbed through the skin (industrial, 5%)
Debate about actual amount that receptor site sees vs. amount taken in
Acute doserefers to single dose, usually high
Chronic doserepeated or continuous low dose over time
Long termlow dose over a life time
Toxicology: Response
3. Response
Nonspecificaffects the whole body system
Burning – destruction of cells caused by exposure to high concentration of strong acids or bases
Narcosisdepression in sensory activity, reversible, caused by alcohols, ethers, benzene
Specific
Damage to excretory organs
Damage to respiratory organs
Damage to reproductive function
Mutagenesis
Carcinogenesis
Acute toxicity– rapid death (usually acute dose causes acute toxicity)
Chronic toxicity related to chronic dosee.g. cases of cancer
Paracelsus principle: The Dose Makes the Poison”
Every chemical is harmful at some level of exposure
How much exposure causes a harmful response????
Every chemical can be toxic, but it depends on the dose
E.g. coffee – hundreds of coffee contain lethal level of caffeine, they will definitely
result in death
About one hundred pills of aspirin is lethal
1 litre of ethanol is lethal too
About 3 litres of water can cause very serious effects
Differently for different individuals
The dose of a usually unknown mixture of chemicals
Measuring manifestations
Endpoint (our bodies are responding because there is something wrong) - physiological manifestation
Can be readily measured
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