Bioaccumulation and Biomagnification
Bioaccumulation
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Bioaccumulation refers to the accumulation of substances, such as pesticides or other chemicals, in an organism.
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Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost.
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Substances accumulate in living things any time they are taken up and stored faster than they are broken down (metabolised) or excreted.
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These are usually fat soluble substances that the body finds hard to get rid of.
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Over time, these substances build up in the fat reserves of the animal. This build up can result in damage to the organism.
Biomagnification
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Biomagnification is the process by which the concentration of a substance increases in the body of an organism as you move up the food chain.
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It is also sometimes referred to as bioamplification or biological magnification.
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Because many substances can be stored in the body for a long period of time, they can be passed from one trophic level to the next, resulting in a greater concentration in predatory animals further up the food chain.
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Biomagnification affects all organisms, but especially those at higher trophic levels in a food chain, such as predators.
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It can lead to poisoning and even death in organisms.
Differences between Bioaccumulation and Biomagnification
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The primary difference between bioaccumulation and biomagnification is the method of gaining the harmful substance.
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Bioaccumulation refers to the way that toxins enter a food chain; this usually occurs when an organism consumes a substance at a faster rate than it can eliminate it.
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Contrarily, biomagnification demonstrates what happens to these toxins as they are passed up a food chain, increasing their concentration.
Examples of Bioaccumulation and Biomagnification
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The most well-known examples of both phenomena involve DDT (dichlorodiphenyltrichloroethane) – a pesticide used widely during the 1950s and 1960s.
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Fish in a lake can absorb DDT directly from water and from the plankton they consume. Similarly, birds that eat these fish will have a higher concentration, and so on up the food chain, illustrating biomagnification.
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When DDT is absorbed by a fish, it struggles to excrete the substance and it builds up in its tissues over time, which is an example of bioaccumulation.
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Another example is mercury in fish. Mercury is absorbed by tiny aquatic plants and animals which are then eaten by small fish, who are then eaten by larger fish. The mercury is passed up the food chain and can result in dangerously high levels in large predatory fish and in the animals – or people – that eat them.