For bear cubs feeding on contaminated milk, that risk is 1000-fold greater, researchers reported in the journal Environmental Toxicology and Chemistry.

"This work is the first attempt to quantify the overall risk of persistent organic pollutants (known as POPs) for the Arctic ecosystem," said lead author Sara Villa, a toxicologist at Italy's University of Milano Bicocca.

For the study, Villa and her team canvassed 40 years of research on the exposure of polar bears, seals and Arctic cod to the deadly compounds.

The data covered bears living between Alaska and the Svalbard Islands above Scandinavia - far less is known about the population in the Russian Arctic.

POPs are easily spread chemicals that can persist in natural environments for decades, and become more concentrated as they move up the food chain.

By the time they travel, say, from plankton to fish to seals to polar bears, these compounds accumulate into highly toxic doses.

Used in industry and agriculture, some are also found in consumer products such as fabric flame retardants. In the 1970s, a class of industrial chemicals called PCBs - found to cause cancer and wreak havoc with hormones - were widely banned, but concentrations in Arctic mammals remained high well into the 1990s.

A new family of pollutants now pose the greatest chemical threat to polar bears, the study found.