Biological magnification is a rising concern amongst researchers who examine the ways that chemicals and pollutants may have long-term effects on ecosystems. In this article, we’ll dive deep into what it is and the impacts it’s already had on our environment.
Biology researchers and students are likely familiar with the field of ecotoxicology, or the study of how chemicals and toxins affect ecosystems and their organisms. In this field, the term biological magnification is frequently used to describe the amplified concentrations of these substances as you move up through the food chain.
Also fittingly called bioamplification or biomagnification, this process explains why harmful substances like have metals, or chemicals found in fertilizers or pesticides, present in even the largest, carnivorous predators.
In this article, we will discuss the process of biomagnification and how it works. We will define the terminology, and then give real-life examples and case studies documenting how chemicals travel through soil, water, and smaller organisms to eventually make their way to the top of the food chain in large concentrations.
What is Biological Magnification?
Put simply; the term biological magnification is used to describe the process by which substances used in farming or produced in industrial waste make their way into and up the food chain.
We see increased levels of these toxins and chemicals accumulating through the trophic levels of the food chain thanks to this phenomena.
Pesticides, fertilizers, and heavy metals from industrial waste are some of the most common culprits who contribute to the problem.
Typically, the materials are carried through water sources like rivers, lakes, and streams as a result of surface runoff where they are then ingested by aquatic animals like frogs or fish. These small organisms are then preyed upon by predators higher up in the food chain, like birds, larger fish, or animals, which is how these same substances make their way into their body.
Many of these toxins and chemicals are fat soluble and get stored in their internal organs or fat tissue. This results in an accumulation of the substance over time and in greater concentrations the higher up the food chain you go. This phenomenon is called food chain energetics.
Although biomagnification doesn’t always have a direct effect on living organisms, long-term exposure to harmful chemicals may result in unpleasant and irreversible side effects that could threaten a species.
Biological Magnification vs. Bioaccumulation
It’s important to note that there is a significant difference between biomagnification and bioaccumulation. Although some may use the words interchangeably, they actually describe different scenarios in an organism.
Biological magnification specifically refers to increasing concentration of materials in each higher link in the food chain. However, bioaccumulation examines the increased presence of a particular substance inside a single organism.
While the two processes may be interconnected, for the purpose of this article it’s important to differentiate the terminology to understand the real-life examples and practice.
Examples of Biological Magnification
There are numerous, well-documented examples of biomagnification where researchers find high concentrations of chemicals in apex predators. Many of these studies also demonstrate the potential negative consequences of this build up over time. Here are a few examples.
During World War II troops faced a plethora of health issues, including outbreaks of malaria, body lice, typhus and bubonic plague spreading through mosquito bites at encampments throughout the world.
DDT is a pesticide that was developed to kill these biting bugs to help control the spread of these diseases, and following the war had agricultural applications. Farmers used the product on their crops to control pests, and it was both popular and widespread thanks to its low cost and easy application.
It was approved as being safe and effective by the EPA at the time because there did not appear to be any harmful side effects of ingesting the chemical in animals or humans. However, this did not take into account the possibility of biomagnification.
DDT doesn’t break down over short periods of time in the environment and is a substance that gets stored in the fatty tissues of animals who consume it. This became particularly problematic for bald eagles.
A predator near the top of the food chain, bald eagles were consuming large quantities of fish who had been affected by the chemical. Runoffs from farms hit the waterways, and DDT infiltrated aquatic plants and animal life, and the eagles ingested the chemical with each meal they ate.
Over time, the chemical disrupted their ability to lay eggs with strong shells, causing the bald eagle population to decrease to the point of near extinction. In 1940, Congress stepped in to pass an act to protect the species, but DDT wasn’t banned until 1972.
It wasn’t just species of eagles affected. Other predator birds like brown pelicans and peregrine falcons saw the same side effects. The thinning off the eggshells made incubation and hatching near impossible and also threatened these bird populations.
Fish and Pregnancy
Another notable example of biomagnification is in predator fish. Species like Shark, Swordfish, Orange Roughy, Tuna, King Mackerel, or Tilefish contain proportionally larger levels of toxic mercury than smaller fish and shellfish.
In fact, the levels are so high that the FDA advises that pregnant women avoid consuming these species for fear of exposing developing fetuses to levels that may cause nerve damage.
How does this toxicity occur? Mercury is introduced into the ecosystem in one of two ways. As a naturally occurring element, it can leach from rocks and volcanoes into our water supply over time, but those natural changes are not likely to significantly impact the environment.
However, when you take the natural occurrences and combine them with human contributions through coal-burning power plants which impact the air, rain, soil, and water around these facilities, the mercury levels rise drastically.
As we now know, once an element enters the water supply, it’s inevitable that it gets ingested by aquatic life at every level of the food chain. When plankton and small crustaceans that make up the majority of the diet of the larger, predatory fish have moderate levels, then the species who eat them will have a compounded effect.
For example, according to the FDA, the average amount of mercury found in a serving of scallops is 0.003 parts per million. Lobsters, one of the main predators of the scallop have a concentration of 0.107 parts per million.
Monkfish love dining on lobster, and have an average of 0.161 parts per million of mercury in their system, and shark and swordfish at 0.979 and 0.995 parts per million respectively regularly dine on monkfish.
In this example, it’s easy to see how quickly the effects compound and how concentrated they become with only four steps up the food chain ladder.
What Causes Biological Magnification?
Although biomagnification is a natural phenomenon that happens in all organisms, the instances where it is worrisome are largely due to anthropogenic factors. Materials that humans introduce into the environment can cause unexpected and hazardous side effects and typically fall into one of the following subcategories.
We live in an age where the word organic is closely correlated with natural and healthy, but too much of anything could be bad. Organic elements like phosphorus, nitrogen, and carbon are necessary for survival, but if they appear in excessive quantities in ecosystems, they may cause eutrophication.
Eutrophication is a phenomenon when an organism that thrives in these conditions, like algae, for example, experience exponential growth and suddenly have an overwhelming population. This can then disrupt the ecosystem and kill off other organisms because there aren’t enough resources, like oxygen, to go around.
Waste produced from manufacturing plants, factories, and other industrial enterprises can release waste and toxins into the air and water that contribute to the problem.
Agricultural and Industrial
Chemicals introduced into the environment from inorganic pesticides, fungicides, fertilizers and herbicides that mix with our natural water sources due to runoff when it rains release toxic elements as well.
Not only does plastic physically impact our environment, often ending up in our oceans and disrupting marine ecosystems, but it can also leach toxic chemicals into water too.
For example, Bisphenol A, or BPA, has made headlines recently as a substance that can produce a range of health conditions in humans that is used in making plastic water bottles. It is one of the leading chemical pollutants in the environment.
As we discussed in our earlier case study, heavy metals that enter our water sources can wreak havoc on the ecosystem. Mining activities are sometimes at fault for releasing deposits that can pollute aquatic plants and contaminate water sources with elements like zinc or cobalt.
Potential Negative Effects of
DDT and mercury aren’t the only hazardous substances that have the potential to biomagnify. Substances like polychlorinated biphenyls (PCB’s) that can impair reproductive systems, heavy metals, polynuclear aromatic hydrocarbons which are a known carcinogenic, cyanide, and selenium have been extensively studied and proven to have similar outcomes.
There are dozens of potential adverse effects to our environment, including but not limited to:
- Reproductive implications for marine and other animal life
- Killing coral reef ecosystems
- Disrupting the natural food chain as species die off
There is also a significant risk of health impacts on humans who consume many of the organisms affected by this process. They include an increased risk of the following:
- Kidney failure
- Liver disease
- Birth defects
- Brain damage
- Respiratory disorders
- Heart disease
Bioamplification isn’t a new phenomenon, but the humans have introduced pollutants to the environment that makes it a threat to the ecosystem and our food sources. Understanding how and why it occurs is the first step to combating the problem and preventing the destruction over time.
Conversations and advocacy for sustainability need to continue to ensure the long-term health of our environment.