Low Amounts of Herbicide Found in Northern Minnesota Lakes

A study has found the weed-killer atrazine in nine out of 10 lakes sampled - including lakes in northern Minnesota far away from farms - leading scientists to believe the chemical is falling out of the sky.

Some lakes in or near the Boundary Waters Canoe Area Wilderness tested positive for atrazine, according to a statewide study of pesticides in Minnesota lakes. The testing was done by the Minnesota Pollution Control Agency and the state Agriculture Department.

"To some people, it is a bit of a surprise, but the concentrations are low, very low," said Steven Heiskary, a researcher with the MPCA.

The concentrations, in parts per trillion, are far below levels considered risky for people, plants or animals, researchers and others said. The maximum level for atrazine is 10 parts per billion.

Fifty-three lakes were tested in 2007. The results, published in a statewide pesticide monitoring report, will be presented at an upcoming conference.

Six of the 46 lakes containing atrazine are in or near the BWCA, including two trout lakes in St. Louis and Cook counties. The only urban lake tested, Lake Nokomis in Minneapolis, had trace amounts of atrazine.

Atrazine is used mainly to control weeds in cornfields and is one of the most widely applied herbicides in North America. When it drains from farmland, it can end up in groundwater and streams.

Bill VanRyswyk, an Agriculture Department hydrologist, said the northern lakes are nowhere near farms - so the likely explanation is that atrazine and other herbicides are spread through the atmosphere.

Pesticides get into the air when they're applied or when wind blows dust from treated fields, VanRyswyk said. Studies by other researchers suggest the chemicals can fall to earth as dust or in rain, he said.

"So it may well be coming in from out of state for those northern lakes," VanRyswyk said.

More lakes are being tested this year, and the state hopes to test the original 53 lakes every few years to measure trends.

Atrazine has been controversial because some research has linked it to extra legs and other deformities in frogs. Syngenta, which manufactures atrazine, denies a connection.