WILLISTON, Vt. -
The search is on to figure out how small traces of herbicides made their way into compost from Green Mountain Compost in Williston.
"Our investigation's not finding any misuse that has occurred in Vermont, so it is not like anybody did anything wrong," said Cary Giguere, the pesticide program chief with Vermont's Agency of Agriculture, Food and Markets.
The team at Vermont's Agency of Agriculture is involved in the effort. It's looking at the yard and food waste and manure that make up the mix.
The compost has been used by roughly 500 homeowners across the state, who have seen their plants wilt and produce smaller crops.
"Our trace back investigation is now focusing on what's coming into the state, whether it's horse bedding, hay or small grains," Giguere said.
Early tests show 5 to 10 parts per billion of the herbicide Picloram in some compost samples. To put that into perspective, experts say 500 parts per billion of the same substance are deemed safe for consumption in drinking water.
"The problem is because at these very low levels they still cause harm to plants," Giguere said.
Thomas Moreau is the general manager of the Chittenden Solid Waste District and oversees compost production at Green Mountain Compost. He says the way the compost is being processed at the new Williston plant could be contributing to the problem.
"Before we used just atmosphere air trying to defuse itself into the pile, now we're really actively blowing air into it so it gets much hotter much faster for a longer period of time," Moreau said.
Right now scientists are trying to figure out if the increased exposure to heat during the composting process is releasing the previously undetected herbicides from plant tissues.
"We feel that these herbicides were always here, but for some reason the new process has made them unsequestered, made them more available," Moreau said.
The Ag department says gardeners don't need to worry about the exposure, but getting to the heart of the problem will be good for their gardens.
"The reason they have not been banned yet as a class of chemicals is because there are relatively nontoxic to humans," Giguere said.
The Chittenden Solid Waste District has already spent $30,000 to have compost samples tested to pinpoint the contaminants and how they made their way into the mix.
The Chittenden Solid Waste District released its September newsletter Tuesday, acknowledging that it is continuing to work with the EPA and herbicide producers to solve the problem and prevent future ones.
