State and local officials who are trying to figure out the source of chemical contamination of Green Mountain Compost have expanded their testing from compost products and “feedstocks” (grass clippings, manure and bedding from horse farms that supply composters) to include feed given to horses.
Chittenden Solid Waste District, which oversees the compost operation, has already agreed to refund $1 million to consumers whose plants were stunted by two persistent herbicides found in Green Mountain Compost.
What appeared at the start to be a local problem, perhaps of misuse of persistent weedkillers, now appears to include all composting operations in the state, the horse farms that supply some composters with manure and companies that supply horse feed, according to Agency of Agriculture officials.
Scientists, several large chemical companies, and state and federal agencies are now trying to identify the source of the contamination. The Vermont Agency of Agriculture, the Vermont Department of Environmental Conservation, two national testing labs, the lab that conducts testing for the state, the U.S. Environmental Protection Agency and Dow AgroSciences and Dupont, which make herbicides, have all been involved in the most recent evaluation of sample results.
The newest set of tests, however, have produced results that did not validate the first three sets. The new information in fact conflicts with those results, the Vermont Agency of Agriculture reported on Friday. The urgency of pinpointing the source of the contamination has led the various collaborating organizations to share their testing protocols for the first time in an attempt to resolve the discrepancies. Results may be available next week, according to officials.
In response to the damage to garden crops from sources that so far appear to have come from out of state, the U.S. Composting Council has already called for banning both clopyralid and picloram. Another persistent herbicide, aminocyclopyrachlor, the main ingredient in the DuPont product Imprelis was banned last fall after its debut in March 2011. It was shown to have killed certain species of evergreens.
The history of the damage to certain classes of broadleaf garden plant such as tomatoes and beans began in June this year, when the Chittenden Solid Waste District received the first of hundreds of reports.
Initial testing for the district by the Idaho lab Anatek showed low but unacceptable levels of persistent herbicide contamination. Tests were confined to feedstocks. But as grazing on pasture was unlikely to be the source — picloram is a Restricted Use pesticide and had not been applied in Vermont for some years and clopyralid is only used on lawns — Moreau said he began to suspect that horse feed was the culprit. Herbicides in grain mixes, which often contain molasses, pass virtually intact through the animal’s digestive system, according to officials.
In late July, feed contamination with clopyralid was confirmed, though not in all samples, with Chittenden Solid Waste District’s third round of Anatek testing.
The next step for the Vermont Agency of Agriculture’s pesticide division was to set up a joint testing process with the U.S. Environmental Protection Agency, the herbicides’ manufacturers Dow Agrisciences and DuPont and the testing lab Carbon Dynamics as well as Anatek to look at the full range of inputs, including feeds such as Purina, Blue Seal and Poulin. The results, which included testing for aminocyclopyralid, did not show picloram in any samples. The tests repeated sampling of compost at several stages of production and of manure and bedding from horse farm suppliers and expanded to include aminocyclopyralid.
