An herbicide that tainted Green Mountain Compost last summer can no longer legally be used on Vermont pastures. But compost companies still worry the chemical will find its way into their products.
The GMC compost, made at the Chittenden Solid Waste District facility in Williston, damaged or killed some broadleaf garden plants, such as tomatoes, costing the district at least $800,000.
The cause of the contamination was found to be aminopyralid. That agent is found in Dow weed-control products Milestone and Forefront and it apparently entered Green Mountain Compost in manure from horses that consumed feed treated with aminopyralid products. Milestone is used to kill up to 85 plant varieties.
The discovery was the result of many months of forensic work by CSWD, the state Agency of Agriculture, the Environmental Protection Agency and pesticide giant Dow Agrosciences.
The identification of aminopyralid as the cause of the compost contamination led to Dow voluntarily changing its labeling of the chemical, ruling out its use on pastures in New England or for any purpose in New York. Any violation, or off-label use, is a federal offense. The new restrictions are aimed at keeping aminopyralid out of horse feed, specifically hay. Horse manure is often a key ingredient in local compost.
Changes in labeling and sales are good news, according to CSWD manager Tom Moreau, but he and other Vermont composters remain concerned about Internet sales of the herbicide and feed, the possible use of older supplies that do not carry the new label and the challenges of enforcement.
Steven Wisbaum, owner of Champlain Valley Compost, told lawmakers at a hearing last session that he sees no reliable way of identifying the source of contaminated manure in future. The Agency of Agriculture, in his view, needs to develop a comprehensive strategy to monitor compost feedstocks to help ensure feedstocks with aminopyralid residues never reach compost operations. Wisbaum also wants the state to identify and prosecute those responsible for illegal herbicide use.
While the state has made Milestone a Class A-Restricted Use herbicide (as Forefront has been for some time), meaning that it is only to be applied by licensed applicators who then report the application to the state once a year, composters like Tom Moreau, who runs the Chittenden Solid Waste District, worry that some farmers might order from out-of-state suppliers.
“Even if it is not sold in Vermont, there is nothing to stop someone from going online and purchasing it,” Moreau said. “And is the consumer even going to read the label?”
The revised federally required label restricts the use of Milestone/Forefront — herbicides for broadleaf weed species — so that they will no longer be used on pasture in New England. If either product has been used in a field as weed killer, hay to be used for feed can only be planted after an 18-month interval, a precaution only one other state, Montana, has instituted.
The U.S. Composting Council took a confrontational approach when similar compost contamination problems occurred in Washington state in 2002. The council sued and settled in 2010 for $23,000.
Vermont took a cooperative approach with Dow.
“I’m not one of those who would go out and hug corporate people,” he says. “We are feeling good. I never thought one of the people I would be thanking would be Dow. They actually came through.”
In initial talks, he found it reassuring that the head of Dow’s regulatory and technical affairs division discussed using compost on his own garden. “He asked me how much I used and when I said two inches, he said he usually put down one and a half,” Moreau said.
Dow Agrosciences spokesman Garry Hamlin said the company often works to address labeling concerns.
“We did not want it to get into compost,” Hamlin said. “When we saw a problem we worked to correct it. The product was not intended to kill people’s vegetables.”
Cary Giguere, head of the pesticides division at the Vermont Agency of Agriculture, and active at the national level in the EPA, worked on the federal label language last winter.
Milestone was developed, Giguere says, as a “low-toxicity” alternative to much stronger previous herbicide formulations. Its limitations emerged as it passed from field — where it initially reached only the intended target, noxious and invasive plants — to animal to compost and then to garden plants such as vegetables and sunflowers.
Problems with manure contaminated with aminopyralid surfaced in the United Kingdom in the early summer of 2008. By July that year, Dow Agrosciences had voluntarily suspended sales and use of herbicides containing aminopyralid in the U.K. Approval was subsequently reinstated in October 2009. Regulators approved reintroduction of aminopyralid after new restrictions aimed at preventing “inadvertent movement of manure from farms” were instituted. They included confining the use of the herbicide to land grazed by cattle and sheep and a ban on its use on land with crops used for forage. The idea was to ensure that if an animal grazed on treated pasture its manure did not end up in compost.
Despite these precautions, The Guardian reported in 2011 that the herbicide had again contaminated compost sold in the U.K.
Finding the source of the problem
When plants showed stunting last June, Green Mountain Compost stopped selling compost immediately and went into high gear as gardeners began reporting damage in tomatoes, peas and other broadleaf plants just as they began to leaf out. At the time, tests by independent labs around the country found several suspect herbicide residues. Dow conducted many tests as well, as the company had the equipment to test minute concentrations — as low as 1 part per billion (ppb) — that can affect plants. Moreau’s garden samples showed 4.6 parts per billion of aminopyralid.
The question was which feedstocks — as inputs for compost are called — should be eliminated and whether the high-heat, high-speed GMC composting process might be a contributing factor in the persistence of the herbicide residues.
In the case of the GMC compost, the culprit, after much testing and many bioassays, turned out to be the persistence of aminopyralid and not the process. GMC takes as feedstocks for its compost horse manure, yard and leaf debris, and various types of food waste, but only horse manure contributed the aminopyralid. A year ago, when the contorted plants started appearing, there were other suspects — clopyralid and picloram, herbicides in the same family as aminopyralid — all of which are used to eliminated broadleaf weeds in pastures, lawns and rangelands.
Aminopyralid, which debuted in 2005, was reviewed and accepted as a “Reduced Risk Pesticide” under an initiative of the U.S. Environmental Protection Agency “reserved for compounds that demonstrate lower risk to the environment and to humans than currently used standard compounds,” according to documents from Dow Agrosciences.
Tests last summer pointed to horse manure as the source of the problem, so it was removed from the GMC feedstock mix. Eventually, researchers traced the source to hayfields or pastures sprayed with Milestone.
As a result of the herbicide contamination last year, the Chittenden Solid Waste District has thousands of cubic yards of contaminated wood chips and tainted compost.
Green Mountain Compost now has a greenhouse where it can bioassay compost as it comes online to be sure it is not contaminated.
Composters are concerned that Dow’s label changes won’t end the contamination problem. Eliminating the sale of Milestone and Forefront in the Northeast and restricting its use nationally on hay and pasture may keep aminopyralid products out of feed — but they say there is a risk from horse feed bought over the Internet.
Steve Wisbaum, in response to a question about ongoing concerns, wrote: “While I appreciate that the label has been improved, I remain concerned about the potential for herbicide residues in feed stocks going to Vermont’s composters both because: A. people often don’t read or simply discount the information on product labels, and B. I still don’t have a clear picture of the Ag Dept’s strategy to discourage and/or monitor for improper use of these herbicides.”
Wisbaum and other composters want the Vermont Agency of Agriculture to make records of herbicide and pesticide applications easily available.
Giguere says the records are kept — “We had exactly eight applications of Milestone last year” — and the agency welcomes calls. The records are not, however, available online.
Editor’s note: This story was updated at 6 a.m. June 10.