Long-Living Sharks Full of Pollutants

Aug. 3, 2007 — Greenland sharks, which inhabit some of the least populated regions on Earth in seemingly pristine Arctic waters, contain high amounts of human-manufactured industrial waste in their bodies, according to a new study.

Since the main source of the chemicals — polychlorinated biphenyls, or PCB's — was banned in the 1970's, the findings show how persistent such compounds are in the environment and how long-lived, top predator species may carry them for decades.

Co-author Ake Bergman, an environmental chemist at Stockholm University, told Discovery News that he and his team decided to focus on Greenland sharks, since their normal lifespan may exceed 100 years, based on an annual estimated growth rate of just a fraction of an inch.

"I noticed that quite a few recently captured sharks appeared to be older than when PCB's were first manufactured in bulk in 1929," Bergman said.

The chemicals were used in a variety of industrial applications, including electrical-related fluids for capacitors and transformers, heat transfer fluids, lubricating oils, pesticides, paints, carbonless copy paper, adhesives, sealants, plastics, and even in surgical implants.

Bergman and his team measured concentrations of PCB's, as well as the industry-related compounds dioxins and furans, in Greenland shark livers and muscle tissue. Dioxins and furans may occur naturally, such as during lengthy forest fires, but not in the amounts seen in today's environment.

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The shark samples came from 10 females that were accidentally caught in trawl or long-line fisheries around Iceland in the North Atlantic.

According to the study, which has been accepted for publication in the Marine Pollution Bulletin, the highest measured concentration was for the world's most toxic dioxin, TCDD, a compound found in the herbicide Agent Orange, which the U.S. military used during the Vietnam War. The herbicide had other applications from 1961 to 1971.

A furan known as TCDF was present in the second highest concentration. This compound is an unwanted byproduct of combustion from power plants, garbage burning and a variety of industrial processes.

"We discovered that Greenland sharks are really subjected to environmental contamination," Bergman said.

He thinks pollutant levels are especially high in the sharks due to their slow metabolism rates as a result of their cold-water habitats. Also, studies show that other apex predators, like bears, large marine mammals and birds high on the food chain, tend to have more contaminants because of "biomagnification through the food web," meaning that as one animal eats another, the substances in their bodies become more concentrated with each step up in the chain.

The health effects of most industrial pollutants remain under debate, but Bergman said, "These contaminants can cause reproductive failures, neurological effects and other problems."

It is unknown how the chemicals might be affecting Greenland shark lifespans because, although the fish may reach over 100 now, they could have lived to even more advanced ages in prior centuries.

Prakash Nagarkatti, a professor of pathology and microbiology at the University of South Carolina, is one of the foremost researchers on environmental chemical pollutants.

Nagarkatti said his lab has demonstrated that dioxins kill immune cells in a process known as apoptosis.

"In this process," he explained, "the cells commit suicide by destroying their own DNA."

Bergman hopes future studies will further illuminate the health effects of industrial chemicals and determine how they may be impacting sharks, as well as humans.

Bergman said, "Sharks provide evidence for what is happening in marine ecosystems, and since we found Greenland sharks carry quite a load of environmental contaminants, there is cause for concern."