The herbicide is showing up at low levels, including in the BWCA, apparently carried by wind and rain.
The widely used weed-killer atrazine is showing up in pristine lakes in northern Minnesota far from farm country, and scientists believe the chemical is falling out of the sky.
In the first statewide study of pesticides in Minnesota lakes, government scientists discovered small amounts of atrazine in nine out of 10 lakes sampled, including some in or near the Boundary Waters Canoe Area Wilderness.
"To some people, it is a bit of a surprise, but the concentrations are low, very low," said Steven Heiskary, a research scientist with the Minnesota Pollution Control Agency (MPCA).
The study shows that pesticides have joined the list of unwanted substances, such as mercury and acid rain pollutants, that are spread vast distances by wind and rain to some of the wildest places in the state.
The tests in 2007 of 53 lakes by the MPCA and the state Agriculture Department also found that 17 lakes contained breakdown chemicals from three other agricultural herbicides. The results were published in a statewide pesticide monitoring report in August and 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. Trout lakes are among the state's highest-quality waters.
The only urban lake tested, Nokomis in Minneapolis, also had trace amounts of atrazine.
The concentrations, in parts per trillion, are far below levels considered to be a risk to people, plants or animals, researchers and others said. The maximum level for atrazine in waterways is 10 parts per billion. No such standard exist for herbicide breakdown products.
Atrazine, used mainly to control weeds in cornfields, 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 who worked on the lake study, said some of the tested lakes probably got herbicides from runoff. Yet the northern lakes that tested positive for atrazine are nowhere near farms, he said. 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 be transported long distances and 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," VanRys- wyk said.
He said additional lakes are being tested this year, and state agencies hope to test the original 53 lakes every few years to measure trends in concentrations.
Some Minnesota legislators also have worried about the herbicide, but efforts to pass tougher state regulations failed in the legislature last year.
Atrazine has been controversial because some research has linked it to extra legs and other deformities in frogs. An Environmental Protection Agency science panel is reviewing the evidence. Syngenta, which manufactures atrazine, denies a connection. The frog deformities were discovered by Minnesota schoolchildren in 1995.
In a statement, Syngenta spokeswoman Sherry Ford said the vast majority of atrazine results were close to the limit of detection, and don't approach any health-based or ecological-based water quality standard.
"These detections are due to technological advances which increasingly allow laboratories to detect substances at levels so low they have no relevance to human or ecological health," Ford said.
It's the spread rather than the strength of the herbicides that worries Samuel Yamin, a public health scientist for the St. Paul-based environmental group, the Minnesota Center for Environmental Advocacy.
"The fact that these chemicals are basically everywhere in the water resources is itself a concern even if the levels in each one are not pushing the health benchmarks," Yamin said.
David Shaffer • 612-673-7090