Last summer’s contamination leads to tighter regulations
By Stephanie Choate
Gardeners who lost their crops of tasty tomatoes, beans and other treats last summer due to compost contaminated with persistent herbicides can take solace in the fact that they helped usher in tighter regulations and improved knowledge.
Last June, gardeners began noticing leaves on broadleaf plants like tomatoes curling and withering. After a saga of difficult testing and false leads, officials from Green Mountain Compost and the Vermont Agency of Agriculture tracked the problem to traces of two persistent herbicides, clopyralid and aminopyralid, both manufactured by Dow AgroSciences.
One year later, aminopyralid—the more potent of the two—is severely restricted in the Northeast and tighter regulations are in place to monitor clopyralid.
After halting compost sales and approving a $1 million compensation package for affected gardeners last summer, Green Mountain Compost officials “began really diving headlong into learning as much as we could about what these herbicides were, how they acted, how they were getting into our compost and how to get rid of them,” said Dan Goossen, general manager at Green Mountain Compost, a program of Chittenden Solid Waste District.
Persistent herbicides used to treat crops such as hay and grain sold as livestock feed can pass into the animals’ manure, make it through the composting process and still kill plants—which is why they are called “persistent.”
Goossen said they learned that clopyralid is far more prevalent than anyone expected.
Clopyralid was found in nearly all the horse manure samples tested, as well as all the major brands of horse feed. It also turned up in grain-based food scraps.
“It’s everywhere,” Goossen said. “It’s ubiquitous…. It’s showing up in bread and pasta that we’re all eating on a daily basis.”
The levels of clopyralid, as well as aminopyralid, are far too low to cause harm to humans or other animals, according to both the Environmental Protection Agency and Vermont Department of Health.
Clopyralid clearly isn’t going anywhere. Composters must manage clopyralid levels to make sure they are low enough to avoid plant harm.
“It becomes an issue of being very careful with how much clopyralid is entering your stream,” Goossen said. “All composters are now faced with the same situation as we learn more about these things…. There’s always going to be some of these persistent herbicides.”
Aminopyralid, however, is trickier.
Goossen said officials believe aminopyralid was primarily responsible for the plant damage last summer. The herbicide can kill plants in amounts as low as one part per billion—or even less—the equivalent of one drop in five Olympic swimming pools.
“It’s a huge problem if it makes it to compost because it’s effective at a tiny, tiny concentration,” Goossen said. “It’s the death knell, if it makes it through to any compost.”
Nearly a year of investigations showed that aminopyralid reached the compost through horse manure from Vermont farms, in particular a farm in Colchester. Since it originated in Vermont, the state had more ability to take action, said Cary Giguere, pesticide program section chief at the Vermont Agency of Agriculture.
Both aminopyralid and clopyralid, as well as some similar compounds, are now designated as state restricted-use pesticides. That means anyone wanting to use them must be a certified applicator and the purchase is recorded and reported to the Agency of Agriculture, making in much easier to monitor.
Giguere also put significant pressure on Dow to change the labeling on its packaging, which carries the weight of law.
As a result, aminopyralid is now prohibited for use on pastures and hay in New England and New York, a significant triumph in a difficult season for composters. The only allowed uses—to keep rights of way, train tracks and guard rails clear—should not make it into compost.
Complicating matters, however, is the difficulty in testing for aminopyralid in compost and manure, which are full of organic matter that interferes with tests.
There is just one lab in the country with equipment sensitive enough for the task—a lab owned by Dow.
For composters, the only feasible and surefire way to test for aminopyralid is to try growing plants in it. Green Mountain Compost plans to test every single batch of compost it produces—growing sensitive plants to make sure they are not affected.
The Vermont Agency of Agriculture is working with Dow and other commercial and state labs to develop testing sites.
“Dow has actually been very helpful…. I think they recognize how dangerous this is for compost, and they’re putting a lot of effort into avoiding this in the future,” Goossen said.
It is unlikely that clopyralid or aminopyralid would ever be banned outright, as the herbicides are a critical agricultural tool and relatively benign in terms of environmental and health impacts.
Green Mountain Compost is not currently accepting horse or cow manure, meaning it has had to rework its compost recipe. It will not sell compost this season.
“This year we’re focusing all of our energies on creating compost that we know will be safe,” Goossen said. “We’re going through extensive testing… once we have those assurances, we’ll begin building up the inventory.”
Goossen expects to resume selling compost in 2014.
He would consider using manure again once tighter safeguards and the ability to test for aminopyralid in a lab are in place, he said.
“It does make good compost, and there’s a lot of it out there with not a lot of other solutions of what to do with it,” he said.
The initial manure-less batches have done well in trials.
“So far, so good,” Goossen said.
More good news is that tests show persistent herbicides break down quickly once mixed down with soil. Samples from the gardens most heavily affected last summer have shown no signs of contamination this year.
Meanwhile, Giguere is still taking a hard look at herbicide regulations.
“There’s still a lot to do,” Giguere said. “Our composters, while they’ll always have to be vigilant about the inputs that they take, we’ve made it a lot safer for them to operate in Vermont.”
Giguere is engaging EPA regulation officials in Washington about whether second-party risk mitigation methods labels—which dictate how people use products grown with persistent herbicides—are effective enough.
“You’ve only mitigated the risk on paper, not in reality,” Giguere said. “The question is how do you actually mitigate that risk of downstream effects?”