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updated 5/20/2011 7:18:56 AM ET 2011-05-20T11:18:56

Toxic chemicals are accumulating in the bodies of dolphins and whales, according to two new studies, and concentrations tend to be highest in the most populated and developed areas.

The findings are not necessarily surprising. Scientists have known for years that the blubber of marine predators harbors pollutants. Still, the new studies offer the most extensive evidence yet that dolphins and whales can be sentinels for environmental contamination. By documenting levels of chemicals in blubber, scientists can now start to gauge the effects of those chemicals on the animals' health and behavior.

The research may also help illuminate potential threats to human health. Dolphins, in particular, eat the same fish we do. So, finding lots of chemicals in a particular geographic pod can signal areas that may not be safe for fishing.

"Dolphins are a nice barometer in some ways for understanding contamination of the immediate environment," said John Kucklick, a research biologist at the National Institute of Standards and Technology in Charleston, S.C.

"If you're concerned about human-health impacts from seafood, that's something to keep an eye on," he added. "They're an indicator of what people might be exposed to."

A number of studies in recent years have revealed a variety of toxic pollutants in dolphin blubber, including PCBs, PBDE flame retardants and the pesticide DDT.

Many of these compounds, which are collectively known as persistent organic pollutants (POPs), have been banned for suspected or proven links to cancer, neurological damage, learning difficulties and reproductive harm, among other health problems for both animals or people.

Still, they are long-lasting chemicals that remain in the environment for years after they are out of use.

To expand on previous, smaller-scale studies, Kucklick and colleagues analyzed 300 blubber samples that had been collected between 2000 and 2007 from male bottlenose dolphins at 14 sites.

All of the animals lived near coastlines, ranging from North Carolina to the Gulf of Mexico and Bermuda. Some areas were rural; others were urban. Some were pristine; others were highly contaminated.

As expected, levels of pollutants in dolphins varied greatly from site to site, the researchers reported recently in the journal Environmental Science & Technology. And certain chemicals showed more drastic patterns than others.

Because bottlenose dolphins are generally homebodies, Kucklick said, chemical levels tended to reflect human activity in the area where they lived. Concentrations of PCBs, in particular, were extremely high in dolphins that live near a Superfund site in Brunswick, Ga.

Compared to Brunswick, PCB levels were lower in the dolphins of Biscayne Bay near Miami, but they were still several times higher there than in animals living further south, in a less populated region near Key Largo.

"The main take-home message," Kucklick said, "is that if a dolphin lives in a city, it's going to have higher levels of contamination."

The scale and scope of the new study highlight a serious potential health problem both for dolphins and people, said Keith Maruya, an environmental chemist at the Southern California Coastal Water Research Project in Costa Mesa, Calif. Still, more research needs to be done to know exactly what the health risks are.

"These bottlenose dolphins that hang around estuaries are a very good sentinel for localized impacts," Maruya said. "Now that we know this one area is really high in POPs, we can do some concerted studies looking at health to see whether there is a link. Dolphins will serve as a good model for what we might expect from human health."

Meanwhile, another recent study by a different group of researchers found a similar pattern in Alaskan beluga whales, this time for set of chemicals called perfluorinated compounds (PFCs).

PFCs are used for a wide range of applications, including as water-resistant and oil-resistant coatings on clothes, food wrappers, cookware and more. They also appear in foams, paints, cleaning products and many other places. These chemicals have been linked to many health issues, including cancer, hormone disruption and developmental problems.

The researchers analyzed liver samples from 68 whales, and found levels of 12 PFCs at much higher concentrations in samples from the remote Chukchi Sea, compared to samples from the Cook Inlet, near urbanized areas of Anchorage.

Still, PFCs turned up in every sample they looked at, the scientists reported in February in Environmental Science & Technology. That suggests that these chemicals travel through the atmosphere and the oceans to just about every corner of the Earth.

"I think it's important to realize that anthropogenic contaminants released at lower latitudes, like in the United States, China and Russia, do end up getting into the Arctic," said lead researcher Jessica Reiner, a research chemist at the National Institute of Standards and Technology in Gaithersburg, Md.

"What humans do doesn't just affect us where we are directly," she added. "It has worldwide implications. It's one world. It's not just your little spot."

© 2012 Discovery Channel

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