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Long-Living Sharks Show Buildup of Toxic Chemicals

(Beyond Pesticides, August 13, 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, including toxic pesticide byproducts. The findings are available online in Marine Pollution Bulletin (in press), entitled “Dioxins and PCBs in Greenland shark (Somniosus microcephalus) from the North-East Atlantic.”

Greenland Shark, Nick CaloyianisAccording to the team of researchers at Stockholm University, the highest measured concentration found is 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 was used for other applications from 1961 to 1971.

The study also names another set of discontinued chemicals, polychlorinated biphenyls, or PCBs, as the main source of the contaminants found in the Greenland sharks. PCBs were banned in the 1970s, which illustrates how persistent such compounds are in the environment and how long-living, top predator species may carry them for decades.

Project leader Dr. Ă…ke Bergman, Ph.D., 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 PCBs were first manufactured in bulk in 1929,” he said.

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

Dr. Bergman and his team measured concentrations of PCBs, 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 at the amounts found in today’s environment. Dioxins, for one, can enter the waterways as byproducts of manufacturing processes and from the use of popular herbicides containing 2,4-D.

Though the health effects of most industrial pollutants remain difficult to quantify, Dr. Bergman said, “[t]hese contaminants can cause reproductive failures, neurological effects and other problems.”

Compared to other areas, the concentrations of contaminants are often low in the fish species consumed by the Greenland sharks in the remote marine environments that they inhabit. However, Dr. Bergman thinks that 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 polar 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.

Dr. 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.”

Another recent study also shows how some organic pollutants, such as lindane, can biomagnify in terrestrial food webs even though the same chemicals do not accumulate in aquatic food webs.

Source: Discovery News


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