It's a small world, we say happily when we meet a friend far from home. But it is truly a small world, and that's not always a comforting thought.

Insecticides used to combat malaria-bearing mosquitoes in the tropics have shown up in fish from Yukon lakes. Chemicals used on crops far to the south are absorbed into the bodies of polar bears off the Yukon's North Slope.

Many of the pollutants detected in Yukon fish belong to a group of synthetic chemicals called organochlorines, which includes PCBs, DDT, toxaphene, and a variety of other substances. Organochlorines can travel long distances and cause problems far from their point of origin.

"Many organochlorines have been banned or restricted in Canada and other countries," says Joan Eamer, Head of Ecosystem Health for Environment Canada in Whitehorse. "But they're still present in the world's environment."

The problem with organochlorines is that they don't break down easily. They persist in the environment, travel in the air, and accumulate in apparently unlikely places.

"Aquatic predators, such as some species of fish or marine mammals, can accumulate organochlorines in their fat," says Eamer.

Organochlorines, especially toxaphene, PCBs and DDT, have been found in fish, polar bears and marine mammals throughout northern Canada. Much is still unknown about the long-term effects of these small amounts of organochlorines on human health or on the health of the animals themselves.

Humans created organochlorines, but natural processes are responsible for carrying them around the world and dropping them in polar regions.

Far to the south, warm air passing over fields that contain residues of pesticides or industrial chemicals vaporizes the organochlorines and carries them along in the wind. As the air cools, the organochlorines condense into droplets. Eventually they return to the earth in rain, snow, or dust.

"A molecule of an organochlorine pesticide might become airborne and return to land over and over again, moving from place to place with changing seasons and weather patterns," Eamer says.

"It's possible that some organochlorines, such as toxaphene, that move easily into air will continue to travel the air currents around the world for years, gradually moving from warmer regions to the colder polar regions."

Ice cores from an ice cap in the high Arctic show that PCBs were deposited in Arctic snow as long ago as the late 1950s. Although the world-wide use of PCBs has declined, the PCB levels in high Arctic snow have not been dropping.

In the early 1990s organochlorine levels were measured in snow at sites in the Yukon and northwestern British Columbia. In areas of low snowfall, the level of PCBs was similar to levels found in the high Arctic, but in the White Pass, where snowfall is high, the total deposition of PCBs over the winter was about 100 times higher.

The concentrations of PCBs and other organochlorines in the snow were still extremely low -- way below the levels that are commonly measured in fish, says Eamer.

"These contaminants enter rivers and lakes through snowmelt and build up to higher levels by becoming concentrated through the aquatic food chain."

The problem of persistent pollutants is not one that can be solved in the north. It requires a worldwide effort to end their manufacture and use. Although use of organochlorines has declined in the past 20 years and levels of many of the chemicals have decreased in the global environment, ending their use won't be easy.

"Organochlorines are cheap to produce and effective," Eamer explains. "For example, there is no current alternative as cheap and effective as DDT for controlling malaria-carrying mosquitoes."

Circumpolar and United Nations organizations are working on ways to phase out organochlorine use throughout the world. Canada is part of a multinational group that is currently developing a protocol, under the auspices of the United Nations, to restrict releases of organochlorines throughout Europe and North America.

"Studies of contaminants in Yukon ecosystems and of the importance of country foods in the Yukon were part of the documentation that convinced the international community of the need for this protocol," Eamer says.

For more information about organochlorines and long-range transport of pollutants, contact Environment Canada (667-3949) or the Yukon Contaminants Committee (667-3272), or see the Yukon State of the Environment Report 1995.