Gerry Whitley goes prospecting in the summer, but he's not looking for gold. He's searching for organochlorine contaminants, like the insecticide DDT, and the tools he uses are frogs.

The idea came to him at a conference in 1995. As Manager of Water Quality for the Department of Indian Affairs and Northern Development in Whitehorse, he was interested in finding a simple way to check for organochlorine contamination in Yukon water bodies and wetlands.

A few years earlier, organochlorines had been found in fish in some Yukon lakes. However, pinpointing the source of the contamination wasn't easy, Whitley says.

"The trouble with fish is they swim around, so they might move a long way from the source."

Then, at that 1995 conference, Whitley heard about the work done by University of Waterloo scientists with spring peepers at Point Pelee National Park in Ontario.

The frogs were collected from areas that had been sprayed with DDT to control mosquitoes. Although spraying had been abandoned 26 years earlier, the frogs' tissues contained significant levels of DDT and related compounds. Since frogs generally live only three or four years, the chemicals in their tissues must have come from contamination lingering in their habitat.

Whitley says he began to wonder if traces of DDT, which was used for mosquito control in the Yukon between 1950 and 1969, might show up in Yukon wood frogs.

"Well, I happen to live beside Paddy's Pond in Hillcrest, and for the last 10 years or so I've been making notes about when I first see the frogs in the spring," says Whitley. "And I know that Paddy's Pond was sprayed with DDT."

Since he didn't have enough money to test large numbers of frogs on the unproved chance that they might show elevated DDT levels, he scrounged enough money to test a small number from Paddy's Pond.

"And there it was -- bingo!"

The results from Paddy's Pond were clear enough to justify wider sampling, says Whitley. Through the summer of 1996, he collected frogs from 14 sites, ranging from Snag airport to Watson Lake.

The results of tests on the tissue samples confirmed the usefulness of frogs in showing the presence of organochlorines, Whitley says. In several sampling locations where the soil had already been tested, the levels of DDT and DDT-related compounds in the frogs matched the levels found in the soil. In one Whitehorse pond, located near soil known to be contaminated with PCBs, the PCBs also showed up in the frog tissue.

The frogs probably pick up the chemicals directly from the soil, says Whitley. Organochlorines are not soluble in water, but they cling in an oily film around particles of damp soil. Adult wood frogs, who spend most of their time in damp patches of forest or on the margins of ponds and wetlands, absorb both the moisture and the chemicals through their skins.

Whitley says the major drawback to using frogs to prospect for organochlorines is simply finding and catching the lively little creatures.

His preferred frog-hunting method is to wade through the shallows at the edge of a pond, carrying a butterfly net for scooping frogs out of the water. Two frog-hunters are better than one, Whitley says.

"But if you disturb a frog on dry ground, you have to drop the net and dive for it with both hands," he says. If it gets away from that first dive-and-grab, the frog is likely to disappear into a tussock, where it's almost impossible to find.

"This is low-tech, curiosity-driven science," says Whitley. "Except for the cost of the lab analysis, science like this is open to everybody."

Whitley's frogs could provide a relatively simple and inexpensive way to answer a number of serious questions about contaminants in Yukon soils. DIAND scientists studying contaminants are now carrying on the frog studies.

The frogs might, in fact, be able to answer other questions, such as the location of contaminating sites and the movement of contaminants in the food chain. However, that would require more understanding of frogs and frog behaviour in the Yukon than is currently available, Whitley says.

"My responsibility is water quality, not frog quality," he says. Learning more about wood frogs is a job for a biologist, either amateur or professional.