Biomagnification: When Toxins Build Up in Nature

Mosquitoes can be irritating! When they bite, they can leave an itchy bump on our skin. Not only that, but mosquitoes can spread dangerous diseases, like malaria, when they bite. Scientists have learned that some chemicals can be used to keep mosquitoes away from us and from the food we grow. DDT is a chemical that can be sprayed on crops to control the number of mosquitoes. However, DDT was banned in the United States of America in 1972. Why?

A mosquito sitting on a plant
A mosquito sitting on a plant, Credit: Yuvallos is licensed under CC BY-ND 2.0.

Chemicals make up our bodies, animals, plants, and ecosystems. Water and table salt are common chemicals. But some chemicals can be dangerous to animal and plant life, even in small amounts. These poisonous chemicals are called toxins. When DDT is sprayed over crops on farms, it helps to keep mosquitoes away. However, DDT can settle into the soil or be carried into rivers by the rain. When this happens, it gets into plants and animals and can be very bad for their bodies. It doesn’t end there! After a plant or animal has ingested or absorbed this chemical, a chain reaction called biomagnification can take place.

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What is biomagnification?

Imagine a bean plant has absorbed DDT from the soil around it. This plant is a food source for squirrels. When squirrels eat the bean plant, DDT enters their bodies. Squirrels can be eaten by larger animals like foxes, so the foxes would also ingest DDT. Over time, the squirrels, foxes, and other animals in the food chain would continue to eat foods that would build up the concentration, or amount, of DDT in their bodies. This can lead to dangerous levels of the toxin and cause problems for these animals. Large amounts of DDT can hurt animal nervous systems and livers, making them sick. This buildup of toxins is called biomagnification, and it doesn’t end in animals.

Diagram showing biomagnification of DDT after it has been sprayed on crops
Diagram showing biomagnification of DDT after it has been sprayed on crops, Credit:

How does biomagnification affect humans?

Humans are also affected by biomagnification. DDT is not the only toxin that can build up in nature. It is one of many organochlorine pesticides (OCPs) that have been banned. Plants and animals are exposed to many other poisonous chemicals. These toxins may not cause an issue right away. This is because toxins only cause problems when they have built up to a specific amount in plants and animals. With lower levels of toxins in their systems, plants and animals can seem healthy.


However, biomagnification means that even if animals and plants are not showing signs of ingested toxins, the harmful chemicals can build up over time. Just like the foxes that ingest DDT through the food chain, humans can ingest toxins from meat and plants that we eat without knowing it. If a person is exposed to a large amount of DDT at one time, that person may become sick, nauseous, and shaky. However, over time, if a person ingests small amounts of DDT, it can stay in their body for years and cause different types of issues. Even after it was banned in the United States, DDT and other OCPs were still detected in a large portion of people tested.

What happens to mosquitoes when they ingest DDT?

With all of the negative effects of using DDT to control mosquitoes, you may be wondering what DDT actually does to them. When mosquitoes encounter DDT, it irritates them and causes them to fly away. If they land on a surface that has DDT on it, they can die. However, some mosquitoes have built up a resistance to DDT and other chemicals like it. This means that they can be exposed to more DDT without dying right away.


The goal of using pesticides like DDT is to scare away any mosquitoes that may carry disease like malaria. However, if mosquitoes become resistant, the chemicals will no longer be useful. Not only this, but the toxins will continue to harm plant life, animals, and humans in the process.

Spraying pesticides on crops
Spraying pesticides on crops, Credit: is licensed under CC BY-NC-ND 2.0.

How can we reduce biomagnification?

What can we do about this? Using DDT can reduce the spread of malaria by up to 90%. Malaria is a very dangerous disease. In some countries, malaria is much more common than it is in the United States. This makes it harder to ban chemicals like DDT in those countries, because it is such a good tool for fighting disease. Scientists continue to research malaria and ways to control it. The more we learn about the disease, the more improved ideas we can find for how to fight it without using dangerous toxins.


Other toxins that build up in nature are easier to control. For example, when we use plastic products, microplastics can get into our water and food supplies, just like DDT. Reducing our plastic use, reusing plastic that we already have, and recycling plastic when we are done using it are all ways we can stop the spread of microplastics in nature. We need to care for our planet and remember that the things we do have consequences for plants, animals, and even humans. We can work together to reduce biomagnification and live in a healthier, happier world.

Litter, including plastics, found in water
Litter, including plastics, found in water, Credit: is licensed under CC BY-NC-ND 2.0.


DDT – a toxin that helps keep mosquitoes away, but can negatively affect living organisms


Chemical – anything with a specific composition of atoms (example: water is H2O, 2 hydrogens and one oxygen)


Ecosystem – communities of plants and animals interacting with their physical environment


Toxins – chemicals that are dangerous for living organisms, even in small doses


Ingest – to eat or take in


Biomagnification – the process of buildup of toxins in nature over time, moving up the food chain


Concentration – the amount of a chemical relative to the amount of liquid, solid, or area in which it is found


OCP – organochloride pesticides; a family of pesticides


Resistance – when an animal, insect, or plant stops responding to a chemical that previously disrupted its function


Microplastics – tiny pieces of plastic that can build up in nature

Flesch Kincaid Score: 65.7


Flesch Kincaid Reading Level: 8th and 9th grade

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  • Tess Bub

    Tess Taggart Bub has a bachelor’s degree in biochemistry and a minor in data science from Houghton College. During her undergraduate studies, she conducted research in the areas of climate science, ecology, and muscle biology. She is currently a PhD candidate at the University of Tennessee Health Science Center studying host cellular response to viral infection. She is a strong believer that science can change the world, especially when it’s shared. In her free time, she loves communicating science, playing guitar and piano, and running. Writing for smore gives Tess the opportunity to help inspire a new generation of women in STEM.