Problems Persist with Persistent Herbicides

The EPA and US Composting Council are working together to solve the problem of killer compost made from persistent-herbicide-contaminated vegetation and manure.
From the US Composting Council
September 19, 2012
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Persistent herbicide residue in compost can cause problems for plants when it is diluted to as little as 10 parts per billion.
Photo by Fotolia/Carola Schubbel


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Posted below with permission is commentary from the US Composting Council about the ongoing problem of Killer Compost. The council is currently working with the EPA and is no longer calling for letters to the EPA, according to Cary Oshins, Director of Education and Outreach.   

Our position at MOTHER EARTH NEWS is that this decades-old problem can only be solved by banning persistent herbicides that cannot be degraded by composting. These potent chemicals simply should not be allowed. It is time to send more letters to the EPA, not fewer!   

To read more about this continuing threat to gardeners everywhere, read  Keep Your Garden Safe From Killer Compost.

Thanks to the pressure of USCC members and allies, USCC President Frank Franciosi and Executive Director Michael Virga, along with Brenda Platt, Chair, USCC Legislative & Environmental Affairs Committee and Dr. Fred Michel, Ohio State University, met with the Environmental Protection Agency (EPA) on August 16th at EPA headquarters in DC. Representatives from EPA included Dan Kenny, Branch Chief, Herbicides Branch and Lois Rossi, Director, Registration Division, and representatives from the Pesticide Re-Evaluation Division, the Environmental Fate & Effects Division and the Biopesticides & Pollution Prevention Division.

Concerned stakeholders from Vermont, Pat O’Neill, Director, Composting Association of VT, Tom Moreau, General Manager, Chittenden Solid Waste District and Cary Giguere, Pesticide Program Section Chief, Agrichemical Management Section, Vermont Agency of Agriculture participated in the meeting via telephone to offer their thoughts and experiences.

Some of the outcomes from the meeting include:

  • EPA confirmed their continued support for composting and the composting industry and has put a priority on investigating the Vermont incident. They are currently on the ground and working with Dow, Dupont and the Chittenden Solid Waste District. Dow and Dupont are involved in a review of methods to analyze contamination. EPA will decide on the appropriate action, pending the outcome of its investigation.
  • EPA and USCC agreed to form a task force to develop a test method to prescreen herbicides for fate-in-compost that will involve experts from both organizations. Will Brinton (Wood End Lab), Assaf Sadeh (Soil Control Lab), Fred Michel (OSU), and Al Rattie (USSC Director of Market Development & STA) were designated to work with EPA on developing the fate-in-compost testing protocol.  These chemicals are up for re-registration in 2014.
  • EPA said they needed to know if the Vermont incident was a stewardship issue, a labeling issue, or a misuse issue. Dan Kenny stated that EPA needed to have a very clear understanding of the source of the compounds that are proving problematic in Vermont before they take any actions on labeling requirements.
  • Mike Virga and Dan Kenny have an open line of communication that will continue until this issue is resolved to the satisfaction of the USCC. Two things under discussion currently include setting up a confidential complaint hotline to report incidents regarding herbicide-contaminated compost and a funding source for composters to defray the cost of remediation for the damage done by these compounds. Funding for both of these items will likely be the responsibility of Dow and Dupont.

This remains a critical issue for the USCC. We will continue to keep our members informed of recent events and progress on action items.

Message to EPA: Time to Stop Persistent Herbicides!

August 1, 2012

Recently Green Mountain Compost, owned and operated by Chittenden County Solid Waste District, Williston, Vermont, suffered a devastating discovery—something in their compost was causing garden plants to distort and wither!  The culprit? A couple of pernicious, persistent herbicides called clopyralid and picloram. This after investing $2.3 million in a state-of-the-art facility designed to recover food waste, yard debris and agricultural wastes from Burlington and the surrounding area. How did these herbicides, which have negligible recorded licensed use in Vermont, get there?  They were probably used on a hay field somewhere to control weeds, the hay was fed to horses, the horses’ manure was sent for composting along with other materials, and the finished compost had traces of the herbicides in sufficient strength and amount to cause damage. It takes VERY little to kill many garden plants, as little as 10 parts per billion. That is like 1 drop diluted in an Olympic sized swimming pool.

Clopyralid and picloram are examples of a relatively new class of herbicides called pyridine-carboxylic acids. Others include aminopyralid and triclopyr. It is clear that regardless of what Dow, DuPont or others put on their labels or try to control their use, they can eventually end up in compost and then in plants that can and will be harmed. All pesticides have to pass a variety of tests before the EPA will register them for use. Tests include toxicity (such as to humans and fish), carcinogenicity, and other potential health and safety issues. They DO NOT include a compostability test. But with the continuing growth of the composting industry, more and more potentially tainted materials will end up in compost, leading to the type of results Chittenden County is experiencing.

Unfortunately problems with persistent-herbicide-contaminated compost are not new or unique to Vermont. Ten years ago clopyralid contamination shut down the compost facility in Spokane, WA. Compost contamination problems have been documented since then in California, Idaho, Minnesota, New Jersey, North Carolina, Ohio, Pennsylvania, and Washington. It’s time for federal action.

We are calling on the EPA to add a “compostability test” to its registration requirements, and set a compostability standard for all chemicals that could potentially end up in a composting facility. We are confident that if the companies had to meet such a standard, they could and would. But if it is not a requirement, nothing else will compel such a change.

We are further urging EPA to (1) immediately initiate a Special Review Process for all herbicides that are pyridine-based compounds and act by mimicking plant growth hormones (auxins), and (2) impose a moratorium on the use and sale of these herbicides pending the conclusion of the Special Review Process. EPA uses the Pesticide Special Review process when it has reason to believe that the use of a pesticide may result in unreasonable adverse effects on people or the environment. The Special Review process involves evaluating existing data, acquiring new information or studies, assessing the identified risk and determining appropriate risk reduction measures.

Persistent Herbicide FAQ/More Information

What are good sources of information on persistent herbicides? 

Websites with Persistent Herbicide in Compost Information:

Is herbicide-contaminated compost a new problem? 

NO! Ten years ago the Colbert compost facility in Spokane Washington was forced to close. The city suffered $4 million in damages and joined a class-action lawsuit with other composting operations against Dow, but only received $23,000 in compensation. Since then, facilities in Pennsylvania, Nebraska and now Vermont have been damaged.

What are persistent herbicides? 

The Environmental Protection Agency (EPA) defines herbicides as chemicals used to manipulate or control undesirable vegetation. Persistent herbicides are a class of systemic herbicides that are used to control a wide variety of broadleaf weeds. These herbicides are formulated to survive multiple years of exposure in a growing environment. We are specifically concerned with the relatively new class of herbicides called “pyridine-carboxylic acids”. They are typically designed for use in hayfields, horse pastures, golf courses, right-of-ways, and lawns to kill off unwanted weeds and to remain effective for several months to years. These herbicides do not impact grasses.

There are a number of compounds that fall into the category of persistent herbicides. The most prevalent are Clopyralid (Dow Agrosciences), Aminopyralid (Dow Agrosciences, 2005), Aminocyclopyrachlor (DuPont, 2010), and Picloram (Dow Agrosciences). Less prevalent compounds in the same class include fluroxypyr, dopyralid, and triclopyr. Many of these compounds appear on labels in slightly different variations making identification by the untrained applicator or a testing lab difficult.

What plants are sensitive to these herbicides? 

Plant families sensitive to clopyralid include

  • Legumes, such as peas, beans, lentils, and clover
  • Solanaceous, such as tomatoes and potatoes
  • Composite, such as sunflower, petunias, daisies, and asters
  • Other plants, such as carrots, carnations, lupines, and lettuce.

What do plants damaged with these herbicides look like? 

Damaged plants will show:

  • Stunted growth: the main growth tip stops growing and the lateral buds begin to grow
  • Reduced fruit set
  • Cupping of leaves
  • Failure of secondary leaves to grow after the seed leaves emerge
  •  In legumes, compound leaves stay single

For photos of herbicide damage:

How long do persistent herbicides last in soil? 

Depending on the type of herbicide and the level of concentration in the soil, persistent herbicides can last anywhere from several months to three or more years before completely breaking down into inert compounds. The length of time depends upon a variety of factors, including the type and moisture content of the soil.

Why don’t persistent herbicides break down in the compost process? 

Commercial composting involves a process of intense and prolonged biological activity at high temperatures. This environment not only results in rapid degradation of food scraps and other feedstocks, but is also extremely effective at degrading the vast majority of any potential herbicide and pesticide residues into their harmless constituent pieces. Persistent herbicides are relatively new compounds that have been formulated by the manufacturers specifically to be resistant to biological degradation. While most residual traces of herbicides typically breakdown in a compost pile in a matter of days, the molecular bonds joining these particular compounds can be resistant for months or even years.

Does exposure to clopyralid in compost pose a health threat? 

No. According to the EPA, it is not harmful to people or animals at the low levels present in compost. In fact, people that have applied this herbicide to their lawns have a much higher concentration of clopyralid in their soil than will be found in compost. The primary environmental concern from this herbicide is its effect on sensitive plants. If vegetables grown in soil treated with herbicide-contaminated compost manage to produce anything, the vegetables are safe to eat.

Where do persistent herbicides come from and how did they get into compost? 

The most common pathway known for persistent herbicides making their way into compost is through manures and bedding as well as leaf and yard debris. Depending on the region, these compounds are used in variable amounts on horse pastures, hay and grain fields, golf courses, right-of-ways, and lawns. The resulting hay, grass, or digested and excreted materials are required to be disposed of somewhere other than a garden or compost facility, or introduced back onto the land of original application. The labeling requirements for many of the persistent herbicides state that manures from animals grazing in treated areas or hay and grass clippings from treated areas are not to be sent to a compost facility.

Why aren’t labeling requirements effective? 

There are a variety of reasons:

  • People don’t read the label
  • People don’t follow the label

In farm use:

  • The information on the use in a field does not get communicated to the hay buyer
  • The hay buyer may sell the hay to a dairy or horse owner without communicating the use of the herbicide-based restrictions
  • The farmer does not communicate the information to the hauler, who brings the manure to a composter

 In urban/suburban use:

  • The applicator may not tell the home or business owner
  • The home or business owner sets the grass at the curb for collection

Why can't composters simply test for contamination? 

  • The test is very expensive, over $300 per test
  • Incoming materials are too heterogeneous to be effectively sampled
  • You have to know exactly which version of which chemical you are testing for. If you test for clopyralid, you may miss aminocyclopyrachlor.
  • It is unfair to place this financial burden on the composter. At the very least, the chemical companies need to establish and make available a fund that composters can use for testing compost feedstocks and products, and a compensation plan for positive contamination.

What federal action is needed to help prevent herbicide-contamination of compost? 

Some states have prevented or curtailed use, but products often move across state borders, so action is needed at the federal level. Despite the fact that the labels are ineffective, the chemical manufacturers are protected by the labeling restrictions, and are thus shielded from being held liable. As we increase recycling and composting – widely recognized as vital to sustainability – these types of persistent herbicides will become more problematic. Requiring ALL herbicides to meet a compostability standard would prevent the problem in the future and spur market introduction of better, more environmentally responsible products. The EPA must initiate a Special Review Process for this entire class of chemicals, which would allow it to assess the situation and take appropriate action. A moratorium on continued sale and use is necessary until the Review Process is complete. Herbicide manufacturers need to be held financially responsible for lab tests and mitigation costs to offset the financial burden on compost producers.


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