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Biomagnification And Persistence Of Chemical Marine Pollution


As the abundance of marine debris in the form of plastics and other trash increases, we have also seen a great increase in community efforts to minimize this trash. It is easy to visualize the damage done in the piles of trash on the beach, mylar balloons floating at sea, and the famous pictures of sea turtles with straws caught in their noses. This has prompted initiatives such as ocean cleanups throughout Cape May, and other coastal areas alike, and even the Cape May Whale Watch and Research Center’s very own Clean Ocean Initiative, which removes floating debris from the ocean. While these organizations have done amazing work for the wellbeing of our oceans, it is essential that we continue to educate the public and recognize other forms of pollution wreaking havoc on the future of marine life. Contaminants, including heavy metals and persistent organic pollutants, from human sources have continually made their way into our marine habitats and have detrimental health effects on the animals living there.Heavy metals can be classified as naturally occurring elements, such as mercury, lead, iron, or copper. These metals are produced through activities in natural sources like volcanoes, or unnatural sources such as mining, gasoline use, burning of fossil fuels or coal, or disposal of electronics as trash. Persistent organic pollutants are chemicals that persist in the environment and can accumulate as they are passed on throughout the food web. These chemicals are toxic to nearly all animals at varying doses. This can include DDT’s (dichlorodiphenyltrichloroethane) and PCB’s (polychlorinated biphenyl). DDT was originally used as an insecticide and was actually banned in 1972 in the United States, yet it still persists in the environment to this day. PCB’s can be found in a long list of common items including paint and cement, electrical wiring, flame retardants, hydraulic fluids, and wood floor finishes. PCB’s were also banned in 1979 and similarly to DDT, have yet to break down in the environment. All of these contaminants can get into the environment, and eventually the ocean, from multiple sources. Industrial and commercial industries, and oil or chemical spills are direct forms of contamination. Before the 1970’s big industries had the ability to dispose of their waste directly into water sources. Indirect forms of contamination can occur miles away from shorelines, referred to as non-point contamination. This can include runoff from roads and storm drains and wastewater and sewage systems. 

This graphic shows the different sources of mercury and how it is released into both the atmosphere and the ocean and the subsequent effects on marine life. The graphic was acquired from the City of Lenoir website.
A visual showing the process of runoff and wastewater contamination reaching the ocean by the Galveston County Health District.

The effects of contaminants in the ocean go far beyond being a physical form of trash. Due to their chemical composition, they are able to bioaccumulate, or build up, in the tissues or fat of living organisms. Then, the act of biomagnification allows these contaminants to pass throughout the food chain after being consumed at increasingly larger concentrations. This leaves those at the top of the food chain to be the most highly affected. Most of these materials build up in the sediments at the sea floor. Marine invertebrates will consume the contaminated sediments, then they will be consumed by larger fish, until it reaches the larger fish, like sharks, and marine mammals at the top of the food chain. As each level of the food chain consumes more than one individual of the level below, its levels of contamination will always be larger. 

This figure, from the Catalina Island Marine Institute, shows how PCB levels biomagnify throughout the food chain until it ultimately reaches the marine mammal population.

It doesn’t take a large amount of these contaminants to be consumed before it can negatively affect the individual. These effects can interfere with normal body processes such as immunity or reproduction. They also can lead to diseases, mutations, and changes in behavior. A study done on mercury toxicity in beluga whales revealed that the response of lymphocytes were reduced with mercury exposure. The average level of mercury in beluga whales is well above the toxicity level for the immune system to work properly. Another test on Steller sea lions showed that they had mercury levels also above the toxicity level, which would lead to negative physiological effects. The study found that those with higher levels of mercury were more vulnerable to oxidative stress due to their diving behaviors. Another study in Sarasota, Florida looked at common bottlenose dolphins and their levels of persistent organic pollutants. They actually found while males continually increase their levels of POP over time, females experienced a decline between age 10-25 before plateauing. The researchers were able to conclude that these chemicals are actually able to be passed to offspring through breast milk. 

Not only do these chemicals affect marine life, but as consumers of seafood, humans also have to worry about their consumption of contaminants. Since humans are at the top of the food chain, we also have to worry about the large amounts of contaminants that have biomagnified throughout the food chain before reaching our dinner plates. Similarly to the marine animals, we experience adverse effects from higher toxicity levels. This consumption can lead to neurological and physiological disorders. One large scale example was in 1956, when vast amounts of methylmercury contaminated the bay and sea of southern Japan from industrial wastewater. This ultimately led to over 2,000 fatalities and a number of disorders ranging from neurological, to vision problems, to comas, all induced from those who ate contaminated shellfish and fish. 

Although the cycle of contaminants throughout our environment may seem to be out of our control, there are actually a number of ways that we can help out. Since runoff is a large part of the movement of these chemicals, we can help by planting more trees, shrubs, and plants to help stop and absorb some of that runoff. Changing the products you buy can also make a difference. Avoiding or minimizing the use of pesticides and fertilizers will decrease the amount of waste, as well as buying less-toxic household chemicals. It is also important to make sure that any chemicals you are using are being properly disposed of such as pet waste, oils, and other chemical household supplies. The combination of our efforts with pollution prevention laws and policies from environmental organizations can make a substantial impact on the future and wellbeing of our diverse marine ecosystem.

Savannah Bickel – Intern at Cape May Whale Watch and Research Center

University of Maine


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