The polar ice cap may not be the only thing shrinking in the Arctic.

The genitals of polar bears in eastern Greenland are apparently dwindling in size due to industrial pollutants, a new study finds.

Scientists report that this shrinkage could, in the worst-case scenario, endanger polar bears on Greenland and elsewhere by spoiling their love lives and causing their numbers to peter out.

In fact, all marine mammals could be affected by pollutants, "especially the Arctic fox, killer whale and pilot whales," wildlife veterinarian and toxicologist Christian Sonne at the National Environmental Research Institute of Denmark told LiveScience.

Arctic animals' bodies, which store large amounts of fat, carry extremely high levels of contaminants.

Polar bears from northernmost Norway, western Russia and eastern Greenland are among the most polluted animals in the Arctic, as they feast on ringed seals and bearded seals.

The blubber of these seals accumulates high levels of organic pollutants loaded with halogens, such as chlorine. These organohalogens can act like hormones.

Sonne and his colleagues looked at formaldehyde-preserved genitals from 55 male and 44 female eastern Greenland polar bears, collected from 1999 to 2002 by polar-bear subsistence hunters regulated by the Greenlandic government.

Harrowing expedition

The researchers experienced harrowing times on their dog-sled expeditions into the wilds of Greenland to study polar bears.

"One evening a bear came just next to us in the night when we were doing the toilette," Sonne recalled. "They shot and it ran."

Another time, "we almost had to eat the dogs as we ran out of food and seals. It was cold sleeping in minus 50 degrees C [minus 58 Fahrenheit] in five weeks with no heater."

The adult polar bear testicles the researchers examined were on average roughly three inches across and 1.8 ounces in weight, although they dramatically enlarge during the height of sexual activity from January to July.

Their bacula, or penis bones, were on average nearly seven inches long. (Most male carnivores and rodents have bones in their penises.)

The scientists found the higher the level of organohalogens in a polar bear, the smaller the testicles and baculum likely were. Ovary size and weight among females also decreased as organohalogen levels rose.

Slow to mate

Polar bears have among the lowest reproductive rates for terrestrial mammals.

Reducing polar bear penis size would thus make sex less successful, upsetting naturally slow-to-grow polar bear numbers, the scientists say. Testicle and ovary shrinkage would upset polar bear reproduction too.

Future research should examine the effects of low levels of organohalogen contamination, Sonne said.

"How long do we have to go down in exposure levels to obtain no-effect levels? Is it possible at all?" he explained.

Sonne and his colleagues reported their findings online Aug. 16 on the Web site of the journal Environmental Science & Technology.

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