Biomagnification is the process of nonlinear or exponential chemical buildup in food chains — the more steps there are in a food chain, the greater the likelihood of biomagnification. 

In 1962, Rachel Carson, a marine biologist and conservationist, released an eye-opening book, Silent Spring, exposing how DDT enters the fatty tissues of animals and humans via bioaccumulation in food webs, causing cancer and genetic birth defects. Her writings ignited the environmental movement and played a pivotal role in the US government’s decision to ban the insecticide.

The concept of biomagnification was popularized by Barry Commoner, a cellular biologist and professor at the University of Washington, in his 1971 book, The Closing Circle: Nature, Man, and Technology. His book detailed how chemicals in the environment, like DDT and dieldrin, accumulate in living organisms and become more concentrated as they move up the food chain. In the decades since, the term has been applied to a wide variety of substances, including pesticides and heavy metals like mercury, arsenic, and cadmium.

Biomagnification is often thought of as a “modern” problem but it's actually a natural process that has occurred since the beginning of life on earth (AKA billions of years). Today, we have a better understanding of the potential consequences of biomagnification and we’re discovering how small choices, like eating smaller fish, can help. 

Let's dive into the science of biomagnification, how to deal with the effects, and why it matters where your food comes!

What Is Biomagnification and Why Should I Care?

It’s how a toxic substance increases along a food chain

Biomagnification occurs when a chemical or element is taken into a living organism and builds up in its tissues or converts into a more toxic form. In this process, the concentration of the toxic substance increases at each step in the food chain; the higher up the food chain, the greater the concentration of toxins in the organisms. This phenomenon is problematic for chronic contaminants like pesticides, which are stored in fat tissues. (Source, Source) 

Biomagnification primarily involves POPs and heavy metals

Persistent organic pollutants, or POPs, such as pesticides, are not easily degraded because organisms haven’t previously encountered them and thus have not evolved detoxification mechanisms for the substances. Similarly, heavy metals are not biodegradable because they are elements, although our liver work in conjunction with the kidneys to eliminate metals from the body in normal circumstances. Both toxic chemicals are lipophilic, meaning they are “fat-loving” and dissolve in fat tissues (which is part of what makes them so challenging to get rid of!). (Source) 

Biomagnification has a “dose-response threshold”

A dose-response threshold is the point at which the concentration of a toxin is high enough to become toxic to the organism. For example, in aquatic ecosystems, the most heavily poisoned fish (e.g., shark, swordfish, king mackerel, and tuna) have been found to contain mercury concentrations that are too high for the fish to tolerate. (Source, Source) 

Government guidelines may not be enough to protect us

In the United States, the EPA is responsible for overseeing pesticide use and setting limits around safe and acceptable amounts of residue that can be left on food. Per the 1996 Food Quality Protection Act, or “FQPA safety factor,” extra protections are required if studies show that a chemical isn’t safe for infants and children. In this case, the cap on pesticide residue is lowered from one one-hundredth to one one-thousandth of the amount found to not harm lab animals. An analysis from February 2020 in the journal Environmental Health looked at 59 pesticide risk assessments and found the agency failed to apply the FQPA safety factor in more than 85% of non-organophosphate pesticides. (Source, Source)

What’s the Difference Between Biomagnification and Bioaccumulation?

Bioaccumulation occurs within an organism when it takes in more of a substance than it can metabolize or excrete — the substance accumulates in that organism. Biomagnification, on the other hand, occurs across trophic levels, or positions on the food chain — as organisms feed on others lower in the chain, the concentration of the accumulated substance is increased, or magnified, at each level. (Source).

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What Does the Research Show About Biomagnification?

Biomagnification almost led to the extinction of the bald eagle

DDT entered the bald eagle food chain through organisms at the lowest levels of aquatic food chains, which were then eaten by fish (the main food source for bald eagles). Researchers found the pesticide prevented birds from properly absorbing calcium, which thinned their eggshells and caused many eggs to break before they could hatch. Because birds of prey like eagles typically only lay a few eggs at a time, losing one or two eggs due to shell thinning had a dramatic impact on their populations. Since the ban of DDT, the population of nesting eagle pairs grew from 487 in 1963 to more than 9,700 by 2006. (Source)

PCBs are wreaking havoc on killer whale populations

In 2017, Scottish researchers found a dead killer whale with one of the highest levels of PCB pollution ever recorded — 100 times greater than the accepted PCB toxicity threshold for marine mammals. High concentrations of PCBs can cause a range of health issues for orcas, including impaired immune function, increased susceptibility to cancers, and infertility. Plus, these PCBs are not only toxic to the animal itself — they're also transferred through a mother whale’s fat-rich milk when she nurses her calves. (Source)

Regulation can make a difference

Thanks to the introduction of national and international controls of hexa- and hepta-BDE congeners and the voluntary phase-out in 2000 of perfluorooctane sulfonic acid (PFOS) production in North America, studies of the Arctic marine biota have found a decrease in levels of flame retardant congener BDE-47 and PFOS. However, the compound hexabromocyclododecane (HBCDD), a different flame retardant, had high levels and was found to be consistently increasing. (Source)

So What Should I Do About Biomagnification?

Eat only low-mercury fish

Unfortunately for all the tuna lovers out there, one of the major sources of chronic, low-level mercury exposure is fish consumption. Although mercury is found in nearly all fish species, farmed seafood tends to have higher levels of heavy metals and other environmental contaminants than wild-caught options. Limit your consumption of larger fish that are especially high in mercury, like tuna, king mackerel, marlin, orange roughy, and swordfish. Instead, eat anchovies, haddock, Petrale sole, sardines, sockeye salmon, summer flounder, tilapia, and trout, which have lower mercury levels. Always opt for wild-caught fish when possible — on top of having a better nutrient profile, they are also better for the planet. (Source, Source, Source)

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Support your “master” antioxidant

Another option is to try boosting your glutathione, a powerful antioxidant that’s at the center of our detox processes. This tripeptide — a compound of three amino acids — directly binds heavy metals and makes them more water-soluble so they can be eliminated in bile and urine and eventually out of our bodies through a process called conjugation. In its active form, glutathione protects cells by neutralizing reactive oxygen species associated with heavy metals. Results are mixed as to the effectiveness of oral glutathione supplements, but you may be able to enhance your body’s natural glutathione production by providing the needed amino acids, especially cysteine and glycine. (Source, Source, Source) 

Sweat it out

Whether it’s through exercise or a warm environment like a bath or sauna, breaking a sweat can help your body get rid of toxins. In a study published in the Journal of Environmental and Public Health, researchers reported that certain chemicals (e.g., arsenic, cadmium, lead, and mercury) are prominent in sweat, while other studies have concluded that induced sweating appears to be a potential method for the elimination of bisphenol A (BPA). Get moving, or if you have access to one, try a sauna. Infrared saunas use light to warm your body directly, rather than warming the air around you, and may be more comfortable if you’re sensitive to heat. Be sure to replenish electrolytes by drinking lots of electrolyte-rich fluids before, during, and after sweating. (Source, Source, Source)

Where Can I Go to Learn More About Biomagnification?

On pollutants in the sea

In this TED talk, marine biologist Stephen Palumbi discusses the trend of bioaccumulation in the sea, and shares a story of dangerous fraud in Japanese fish markets, where consumers were tricked into buying contaminated dolphin meat, liver, and blubber labeled as whale meat. (Source)