Once in the north, the chemicals break down slowly due to the relative absence of sunlight and warm temperatures.
"Killer whales can be regarded as indicators of the health of our marine environment," Wolkers said. "The high levels of contaminants are very alarming.
"They clearly show that the Arctic seas are not as clean as they should be, which in particular affects animals at the top of the food chain."
When animals ingest chemicals such as PCBs, the toxins are not broken down in the body but are instead stored in fatty tissue. Such chemicals are known as persistent organic pollutants.
Through a process called bioaccumulation, animals higher up in the food chain ingest and store higher concentrations of these chemicals. Because the toxins bind themselves to fat, blubber-packing Arctic animals are particularly susceptible.
Killer whalesknown as the wolves of the seaare top Arctic predators, eating prey that includes fatty animals like walruses, seals, sea lions, and even other whales.
In addition, fat-loving toxins may have a direct impact on the next generation of whales through mothers' milk. Marine mammals produce milk that is 30 to 70 percent fat.
"When they use those fat reserves for nursing their young, those toxins are in the breast milk, and it exposes the young to high concentrations at the critical time when they are developing," WWF's Walker noted.
No Quick Fix
The effects of these toxins have not been studied in the whales, and Wolkers of the Norwegian Polar Institute plans to begin such a study next year.
But in other large Arctic animals, such as polar bears and seals, these toxins are known to cause serious health problems.
"A lot of the chemicals, like PCBs, affect the hormonal system and some of them affect reproduction, so we're concerned about [the whales'] pregnancy and about calf survival," Walker explained.
Walker also reported that studies show the toxins have impacts on hormones that control metabolism, and also on the immune system's ability to protect animals from disease.
Meanwhile, experts warn that there is no immediate solution to reducing the amount of toxins in the Arctic. For example, some of PCBs revealed in the killer whale study were widely phased out in the 1980s.
"We don't know how long some of these chemicals are going to persist in the environment," said Walker, who urged governments to ban hazardous chemicals whenever possible.
PCBs and many harmful pesticides are already banned under the Stockholm Convention on Persistent Organic Pollutants, which came into effect in 2004. Many had been phased out for two decades prior to the convention.
But most brominated flame-retardants, used on products from rugs to computers, are not banned and are still heavily employed.
Helen Bjørnøy, the Norwegian Minister of Environment, said in a statement that she'd like to see that change.
"The toxic contamination of killer whales clearly shows the result of an unsustainable use of chemicals internationally," Bjørnøy said.
"This is one of the greatest global environmental threats. The EU ministers now have the possibility to strengthen the chemicals legislation in Europe, and I urge them to use it."
Walker commented that although many chemicals are long-lasting, the positive effects of reduced use begin much sooner.
"The good news is that if you look at those [toxins] that have been banned under the Stockholm Convention, their levels are dropping in the environment," she said.
"Just because a toxin has been banned you don't get rid of it immediatelybut we do see a difference. The sooner we stop using them the better."
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