Biomagnification of Toxic Chemicals Through Ocean Ecosystems to Humans
“Because humans are at the top of food webs, we get very high concentrations of toxic chemicals that we are responsible for releasing into nature in the first place.”
One of the most important and influential books in modern biology is Silent Spring, published in 1962 by marine biologist Rachel Carson. Carson studied the effects of large-scale synthetic pesticide use in the 1940’s and 50’s and found that pesticides cause serious ecosystem-level damage by harming and killing numerous species beyond target pests. Carson showed that DDT (dichlorodiphenyltrichloroethane)—a synthetic pesticide used globally to control insects on agricultural crops—was not only killing insects, but animals that ate plants and insects sprayed with DDT, and animals that ate those animals, and so on all the way up the food web to humans. DDT was known to cause reproductive, tissue, and organ damage in numerous species and was later linked to cancer in humans and other animals.
1962 first edition cover of Silent Spring by Rachel Carson.
Publication of Silent Spring eventually resulted in global bans on DDT and many other toxic chemicals indiscriminately released into nature. Unfortunately, in the 60 years since Silent Spring, the quantity, types and ubiquity of toxic chemicals around the globe has only increased, as has their release into the environment. To make matters worse, many toxic chemicals are persistent, meaning once they enter an ecosystem it is very hard to remove them so their damage can last for decades, even centuries. Toxic chemicals can even damage DNA, resulting in permanent genetic defects in affected individuals and ultimately populations.
Living organisms are constantly exposed to toxic chemicals that are both natural and man-made. They have evolved ways (livers, kidneys, excretion, etc.) of dealing with toxic chemicals that occur in nature in normal concentrations. But they have not evolved ways to handle certain types of man-made chemicals, especially those that can’t be easily dissolved and excreted out of the body. Instead, toxic chemicals that can’t be eliminated from the body are sequestered and stored in fat cells and other tissues so they can’t do major physiological damage.
The process of toxic chemicals being transferred up food webs is called biological magnification or biomagnification as opposed to bioaccumulation in which toxic chemicals are accumulated in a single organism. The problem is when an animal further up the food web eats a lot of plants and animals that have bioaccumulated toxic chemicals. The more they eat, the higher the concentration of toxic chemicals they are ingesting, and they in turn store these chemicals in their own tissues. This is biomagnification. The concentration of toxic chemicals gets higher and higher further up the food web as animals eat a lot of smaller animals with stored toxins. Eventually, the concentration of toxic chemicals becomes so high in animals throughout food webs that they (and their offspring) develop physiological problems, get sick, and often die. Because humans are at the top of most food webs, we can get very high concentrations of the very same toxic chemicals that we are responsible for releasing into nature in the first place.
Biomagnification of DDT through an ocean ecosystem to humans. Biomagnification is the increasing concentration of toxic chemicals up trophic (eating) levels in a food web. The DDT concentration (X) is in parts per million. As the trophic level increases in a food web, the concentration of toxic chemicals also increases. The X’s represent the concentration of toxic chemicals increasing as the trophic level increases. Toxic chemicals are stored in a living organism’s tissues and fat. Predators accumulate higher toxins than their prey. Illustration credit Wikimedia Commons.
Everything eventually ends up in the ocean
Elevation on land is measured using sea level as the lowest point, or elevation zero. What this means in practical terms is that almost everything on land eventually ends up in the ocean because of wind and water and other forces. Wind blows trillions of tons of dust, chemicals, trash, and other stuff into the oceans annually. Water—in the form of rain, runoff, streams, rivers, wetlands, ground waters, etc.—ultimately drains into the oceans carrying with it trillions of tons of eroded land, chemicals, trash, and other pollutants from every source imaginable. Plastic trash that ends up in the oceans releases toxic chemicals as well. As a result, the oceans have become deadly repositories of very large amounts of persistent toxic chemicals created by humans.
The solution to pollution is NOT dilution
For centuries, the oceans have also been used by humans to dump their waste—including toxic chemicals—from residential home drains and sewers to industrial waste pipes flowing directly into the sea. A common slogan that continues even today is that “the solution to pollution is dilution” with many advocating for ocean dumping because the oceans are too big to fail and water is the universal solvent that eventually breaks everything down. Manufacturers of toxic chemicals have dumped barrels of industrial waste off boats into pristine ocean habitats. A notorious chemical manufacturer in Los Angeles dumped a half million barrels of DDT in the ocean off Catalina Island from the 1940’s to the 1980’s. The solution to pollution has never been dilution. The real solution is not to create, use, and dump toxic chemicals in the first place. Our current stockpiles should be used with extreme caution and understanding of the effects on ecosystems and excess should be disposed of safely and properly.
Biomagnification of toxic chemicals through ocean ecosystems
DDT has since been found throughout the Santa Monica Bay ecosystem in microscopic plankton, fish, pelicans, sea lions, dolphins, and humans. It took decades of investigative research to trace the fate and biomagnification of DDT throughout this ocean ecosystem and the story is still incomplete. But DDT is only one of 100,000 toxic chemicals that end up in our oceans from thousands of point and non-point sources.
Point sources are easily identifiable because toxic chemicals originate from a single place or point. Non-point sources are harder to identify because toxic chemicals originate from several locations and are delivered to the ocean by wind and water as described above. Some sources can be both, like factories, farms, wastewater treatment plants, boats, car tires, and so many more.
The end result has been the accumulation and concentration of man-made toxic chemicals in the oceans over centuries that ocean wildlife can’t escape. It is likely that millions to hundreds of millions of ocean animals die each year from exposure to and ingestion of toxic chemicals (bioaccumulation) and that some species may go extinct as a result. But these numbers are impossible to know with any certainty. This problem is further exacerbated by biomagnification of toxic chemicals through ocean ecosystems all the way to humans who eat seafood and swim in toxic seas.
As Rachel Carson put it many years ago, “this is the reckless and irresponsible poisoning of the world that man shares with all other creatures.”
How you can make a difference
Dispose of your home waste properly
Keep litter, pet wastes, leaves, and debris out of street gutters and storm drains since these outlets drain directly to lakes, streams, rivers, wetlands, and ultimately the ocean.
Dispose of used oil, antifreeze, paints and other household chemicals properly—not in storm sewers or drains. If your community does not already have a program for collecting household hazardous wastes, ask your local government to establish one.
Clean up spilled brake fluid, oil, grease and antifreeze. Do not hose them into the street and sewers where they can eventually reach the ocean.
Minimize your use of toxic chemicals at home
Apply lawn and garden chemicals sparingly and according to directions.
Purchase household detergents and cleaners that are low in phosphorous and toxic chemicals to reduce the amount that makes it to the ocean.
Maintain home areas to minimize toxic runoff
Control soil erosion on your property by planting ground cover and stabilizing erosion-prone areas.
Have your septic system inspected and pumped, at a minimum every three to five years, so that it operates properly.
Engage in local, state, and federal legislative actions
Encourage local government officials to develop construction erosion and sediment control ordinances in your community.
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