A contaminant, also called a pollutant, is a substance or radiation that can have harmful impacts on one or more ecosystems. It has the ability to modify the physical, chemical, or biological properties of an environment or an organism.
Contaminants can be classified in several ways: by source, nature, toxicity, mode of action, or persistence. For example, when classified according to their nature, three categories emerge: chemical contaminants, biological contaminants, and physical contaminants.
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Nature of contaminants |
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Chemical contaminants |
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Biological contaminants |
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Physical contaminants |
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The toxicity of a substance is an assessment of its potential to harm a living organism. It depends, among other things, on the nature of the contaminated environment, the concentration of the contaminant, the type of organisms that are exposed, the duration, and nature of the exposure.
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The toxicity threshold, on the other hand, is the minimum concentration of contaminant that causes harmful effects to a living organism.
Each contaminant has its own toxicity threshold. However, different factors can impact this toxicity.
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Concentration: The higher the concentration of a contaminant, the more likely it is to be toxic.
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The nature of the contaminated environment: The contaminant can have a different impact depending on the environment in which it is found (e.g.: water, soil, etc.).
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The type of organism with which the contaminant is in contact: Contaminants are toxic to some organisms while others remain unaffected by the same substance.
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Duration of exposure: The longer an organism is in contact with a contaminant, the more likely it is to be poisoned by it.
In humans, the toxicity threshold for mercury (Hg) is |200| microlitres per litre of blood. When this value is exceeded, there are serious health risks for the individual. It can, in fact, attack the kidneys as well as the nervous system.
Acute toxicity is the term used when the harmful effects are felt immediately. When the effects appear long after exposure or if the exposure has been over a long period of time, but at a low concentration, it is called long-term toxicity.
The lethal dose 50, known as LD50, is the dose of a contaminant that causes death in 50% of the individuals exposed to it. The lower the LD50 value, the more toxic the substance.