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Describe bioaccumulation and biomagnification and their effects.

Bioaccumulation

Bioaccumulation is a problem where small, seemingly harmless amounts of something received over long periods of time eventually reach toxic levels because the body has no way to metabolize these compounds.

The concept of bioaccumulation, a series of fish icons increase in size and change color from blue to orange, indicating an increase in contaminant levels over time. — ***Bioaccumulation occurs in individual organisms over periods of time because they continue to consume contaminants over their lifetime.***

Bioaccumulation occurs when small amounts of a substance are consumed by small organisms such as phytoplankton. To obtain their nutrition, phytoplankton must filter large quantities of water. As they filter water, they obtain nutrients such as nitrogen and phosphorus. If the water also contains human-made chemicals such as DDT or polychlorinated biphenyls (PCBs), these chemicals will also be taken up by the phytoplankton. Since they cannot metabolize the chemicals, the phytoplankton will have increasing levels of them retained in their structure, especially in any storage cells such as fat cells. This bioaccumulation then leads to biomagnification in the food chain as other organisms such as zooplankton and small fish feed on vast quantities of phytoplankton.

Essential Knowledge

Bioaccumulation is the selective absorption and concentration of elements or compounds by cells in a living organism, most commonly fat-soluble compounds.

Biomagnification

When bioaccumulation becomes compounded through a food chain, it is called biomagnification. These phenomena most often occur with heavy metal pollution, such as mercury or lead.

The concept of biomagnification, with smaller fish icons leading to a larger seal icon and then to an even larger bear icon, each changing from blue to orange, representing the transfer and increase of contaminants up the food chain. — ***Biomagnification is where contaminant concentrations increase at each level of the food chain in an ecosystem.***

For example, if mercury is released into a waterway, even in low doses, the plankton will absorb the low dose and will be unable to process the mercury. When the plankton are eaten by a larger fish that requires many plankton to survive, the larger fish will have the mercury from all the plankton in its body. Then, an even larger fish may eat the smaller fish. This larger fish will need many smaller fish to survive, so it will have all of the mercury that was in the smaller fish, resulting in even higher levels of contamination. This process repeats up the food chain until apex predators (like us!) have very high levels of contaminants in their bodies.

Essential Knowledge

Biomagnification is the increase in concentration of substances per unit of body tissue that occurs in successively higher trophic levels of a food chain or in a food web.

Effects of Bioaccumulation and Biomagnification

If substances are not persistent, they biodegrade (become broken down by natural factors) and do not accumulate nor magnify. But persistent substances can cause bioaccumulation and biomagnification in ecosystems, such as heavy metals (mercury, lead) or persistent pesticides (DDT), when they are used in or around aquatic ecosystems.

Bioaccumulation can cause...

Disruption of physiological processes when accumulating toxins interfere with normal biological functions.
Impairment of organ function when accumulated substances damage vital organs, affecting their ability to function properly.
Damage to the nervous system when neurotoxic substances can lead to neurological damage and affect cognitive and motor functions.
Increased risk of chronic diseases when long-term exposure to bioaccumulated toxins increases the risk of developing chronic health issues.

Biomagnification can cause...

Health Risks including cancer, kidney diseases, liver failure, birth defects, respiratory disorders, and heart diseases.
Ecosystem Disruption affecting reproduction and development in animals and leading to the destruction of ecosystems.
Predator Impact when predators accumulate higher levels of toxins than those lower in the food chain, which can result in their death or significant population declines.

Both processes work together to make them a significant environmental issue, such as in the following examples:

Essential Knowledge

Some effects that can occur in an ecosystem when a persistent substance is biomagnified in a food chain include eggshell thinning and developmental deformities in top carnivores of the higher trophic levels.

Humans also experience harmful effects from biomagnification, including issues with reproductive, nervous, and circulatory systems.

DDT, mercury, and PCBs are substances that bioaccumulate and have significant environmental impacts.

AP Exam Tip

You need to know the difference between bioaccumulation and biomagnification.

You need to know the effects of both processes.

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