Herbicides and Compost A Closer Look

Sept. 1, 2002
Whether used as a soil amendment, as a growing medium for groundcover, or as the groundcover itself, compost plays an important role in erosion control. Water-retaining and full of organic matter, compost’s role is to enhance vegetation growth. However, some now believe “hidden” ingredients could retard, or even destroy, plant growth. Because of this possibility, compost is now under scrutiny from industry organizations and some state governments.Current concern centers on clopyralid (klow-PEER-ah-lid), a Dow AgroSciences herbicide that’s been used in the United States since 1987. Available under a variety of brand names (Millennium, Transline, Stinger, Reclaim, Confront, Curtail, Scorpion, Hornet, and Accent Gold), clopyralid is being found at various levels in compost throughout the country.In October 2001, the US Composting Council (USCC) delivered a position paper on clopyralid and composting (www.compostingcouncil.org/article.cfm?id=35) in which it states “compost products from clopyralid-containing feedstocks (including grass clippings, animal bedding, and manures) have damaged non-target crops due to the presence of clopyralid.” The paper further states that, although other clopyralid-containing chemicals were of concern, “to date the most serious problem appears to be associated with grass clippings treated with the Dow AgroSciences product Confront.”What’s the source of all this Confront? Yardwaste is a likely culprit, as many commercial and residential lawn services use Confront in their herbicide mixes. Why hadn’t the clopyralid problem shown up sooner? One reason is that, until recently, few composting companies tested for the chemical. Another probable explanation is that in many parts of the nation, excluding grass clippings from household waste is a “new” procedure. In years past, grass clippings and other residential yardwaste went into landfills along with other household refuse. Even today a certain amount of grass clippings still ends up in landfills; many waste companies use the clippings as their daily cover.Confronting the Clopyralid IssueAccording to the USCC, clopyralid-contaminated compost has caused “documented damage” in Washington, Pennsylvania, and New Zealand, and “additional cases continued to be reported.” Washington State University (WSU) first discovered herbicide-tainted compost in 2000, when picloram (closely related to clopyralid) was detected in compost the university farms and research facilities produced from animal manure and bedding. According to the university’s study, the contamination stemmed from a herbicide-treated pasture that had been harvested for hay; the hay was fed to WSU livestock and also used for the animals’ bedding. The resultant manure and soiled bedding was taken to the WSU composting facility. The eventual compost from this batch was sold to nurseries and homeowners, who discovered “plant-deforming symptoms on peas, beans, tomatoes, potatoes, sunflower and certain shrubs.” After this incident, WSU instituted a regular testing program for herbicides, which included both analytical tests and bioassay with plants.In spring 2001, WSU’s compost was found to contain clopyralid in concentrations from traces to more than 200 parts per billion (ppb). Once again the contamination source was believed to be the grass hay and straw used in animal feeding operations. To protect its compost product (approximately 25,000 yd.3 annually), WSU now certifies vendors of grass hay and straw, who must guarantee their products are free from herbicide contamination.
Reacting to reports of clopyralid-tainted compost, earlier this year the Washington State Department of Agriculture banned the use of clopyralid herbicides on residential and commercial lawns and turf. Clopyralid products may be used on Washington golf courses only if no grass clippings, leaves, or other vegetation from the sites are sent to composting facilities that provide product to the public.Loading materialUnloading yardwasteGrinding materialPenn State University began composting campus landscape debris, preconsumer dining-commons food residuals, and dairy manure in 1997. The wastes were composted in windrows, and the finished product was used in campus landscaping. In 2000, the campus compost began to be used for vegetable crop research. Penn State researchers studied two compost application rates: Some areas received approximately 1.5 in. (applied to the soil surface and incorporated), and others received approximately 3 in.In their study, which began with bell peppers, Penn State researchers noted plant abnormalities that resembled those caused by 2, 4-D (dichlorophenoxyacetic acid). Samples of the compost used on the bell peppers were submitted to a laboratory. Although no 2, 4-D was found, clopyralid residue between 10 and 75 ppb was detected. Compost with the lowest residue had been exposed to rain and snow and was approximately a year old. Samples with higher residue had been collected from windrows immediately prior to curing. In tracking down the clopyralid source, the researchers discovered landscape debris contained the chemical. The trees were not sprayed, however; how could leaves be the source? Further investigation revealed possible answers: overspray from turf applications, translocation, and/or minimal grass collected when the leaves were vacuumed. More leaf debris was tested, and this time any grass included was separated and tested individually. The grass, which comprised less than 1% of the samples’ weight, contained clopyralid residue of 573 ppb. Leaves from the same samples contained 36 ppb. The grass was the clopyralid source. Since the herbicide residue was discovered, Penn State has ceased using any clopyralid-containing chemicals for turf applications.Penn State vegetable crop-growing trials with the tainted compost continue so that the phenomenon can be carefully documented to develop identification and remediation recommendations for vegetable growers. In 2001, the contaminated compost was used in the production of leafy greens, culinary herbs, and onions, and the bell pepper study entered its second year. Initial results from the bell pepper study moved Penn State researchers to conclude “the latter study is revealing that, given certain conditions, clopyralid can persist for more than two years after application and incorporation into the soil.”Conflicting DataWilliam Brinton Jr., Ph.D., president and founder of Mt. Vernon, ME’s Woods End Research Laboratory, has been performing bioassays on clopyralid-tainted compost. He disagrees with Penn State’s “two-year” conclusion.“We’re finding clopyralid doesn’t do as much damage as some think,” he says. “It takes a huge amount of it to do damage, contrary to some assertions. We’re finding it dissipates in the soil faster than other studies say.”Brinton’s studies on clopyralid involve bioassays–growing plants in potentially contaminated compost. “We make sure no other chemicals are in our samples–clopyralid, but nothing else. For example, salts, which are usually found in all compost, will damage any plant. We have to dilute some samples to achieve varying parts-per-billion. We also have to make sure the compost is properly cured.”For his clopyralid studies, Brinton included winter wheat, garden beet, sweet basil, Japanese buckwheat, radish, cucumber, lettuce, tomato, peas, dwarf sunflower, and red clover. Based on his findings, Brinton predicts clopyralid-tainted-compost crop damage will appear mainly at higher concentrations for most of these crops. Winter wheat, garden beet, sweet basil, Japanese buckwheat, and radish should show no damage even when subjected to compost containing 200 ppb of clopyralid at an application rate of 200 tons/ac. At that same application rate, cucumbers and lettuce would show moderate damage, and tomato, peas, dwarf sunflower, and red clover would experience extreme damage.According to Brinton’s predictions, tomato, peas, dwarf sunflower, and red clover should exhibit varying degrees of sensitivity to clopyralid (see Table 1). Even red clover, a “litmus paper,” or the canary in the coal mine of plant sensitivity, shows no or slight damage at most concentrations. A full report of Brinton’s findings were published in the April 2002 issue of Composting News.
Table 1. Projected Crop Damage From Clopyralid in Applied Compost (in soil, day-40 estimate)Clopyralid in Compost, ppb (dry)10 ppb50 ppb200 ppbCompost Application Rate (tons/ac.)5020010502001050200TomatoNNNNSNSEPeasNSNS MSMEDwarf SunflowerNSNSMSMERed CloverNSNSMSMEN = No damage, S = Slight damage, M = Moderate damage, E = Extreme damageOther species exhibited similar clopyralid resistance. “For a Washington state study involving roadside use of clopyralid, we wanted to find out how it would affect wildflowers. Of 11 species, we found only silky lupine and cornflower were damaged by a clopyralid level of 200 ppb,” Brinton reports. “If anyone was concerned about clopyralid contamination, lists are published of plants that are sensitive to clopyralid–all you’d have to do is not plant those in that particular field the next year.”What’s the “Cure”?Brinton believes some of the clopyralid-contamination problem lies in the compost curing process. “In our study, we found it takes 100 to 120 days for manure or compost to be stable. The problem with commercial compost seems to be that most grass clippings get ‘composted’ in 40 days! That’s certainly not enough time. However, if you were to tell composters they have to wait a year to send out product, they’d tell you you’re crazy.”In the June 2002 issue of Resource Recycling, Brinton published results of a survey of composters nationwide. The survey revealed that the respondents’ average compost process (total active and curing time) was about 12 months. Brinton, however, uncovered surprising variances in reported active composting phases, ranging from three days to five years.In addition to time, industry technique might not be adequate for breaking down compost, let alone any clopyralid that might be included. “We’ve seen a lot of degradation, if the compost curing piles are warm and generally moist. However, composters like their product dry and ‘crumbly,’ which doesn’t allow the material to break down. We’re concerned about the taking of shortcuts in breaking down compost,” Brinton says.Even composting on a much smaller scale–in a backyard, for example–requires more care and time to complete. As microorganisms actually perform the process, compost becomes almost a living thing, requiring water and air. Because the decomposition process produces heat (the optimum temperature is 150°F), moisture and air must be present to keep the temperature from reaching levels that would kill the beneficial microorganisms. To aerate the pile, backyard compost needs to be turned at least once a week (more during periods of excessive rain), and moisture must be added if the compost becomes dry (less than 40% moisture). Despite all this care, compost will rarely be garden-ready by fall; many gardeners allow it to weather through the winter before adding it to garden beds.How Much Concern?Brinton’s survey also asked respondents to note their concerns. Only 4% of the respondents expressed concern over clopyralid and/or picloram contamination. “By comparison, 36% complained about nonorganic stuff–plastics, metals, glass–in the compost stream,” Brinton says. “Probably in any major city in the US, composters will find clopyralid in their material,” reports Rob McCartney, general manager of Kurtz Brothers, a Columbus, OH, composting firm that participated in the survey. “It’s the number-one broadleaf control, used by the largest lawn care company in the world, TruGreen ChemLawn. But even though we produce 300,000 yards of compost a year, we have never had a complaint about clopyralid contamination. Maybe we have diluted it enough; our composting process takes nine months. Also, we’re learning how to monitor and test for it.”Eighty percent of Kurtz Brothers’s raw material comes from commercial sources, such as tree trimmers; the rest comes from area municipal yardwaste. “We are isolating our grass clippings, covering them with wood chips, then we test those,” McCartney says. “We have a scientist on staff who monitors quality. We would never let product go out that would be detrimental.”Kurtz Brothers often has samples tested by Brinton’s Woods End company. McCartney is aware of possible clopyralid problems, and he has kept up with current research. “The Penn State research was all done in greenhouses, with trickle irrigation,” he says. “Real-world compost isn’t treated like that. We’re hoping to find what’s an ‘acceptable level’ of clopyralid in compost by helping with research at Washington State, Penn State, and the Ohio Department of Agriculture. However, even if it was banned right now, we’d probably still see clopyralid in chemical tests for the next two years.”Although the USCC has been critical of Dow AgroSciences, McCartney thinks the clopyralid manufacturer is trying to become part of the solution. “Dow is being very helpful,” he reports.“Dow took clopyralid out of consumer use; now you have to be a pro to use it,” Brinton adds. “They’re also financing the investigation of it and how to use it.”Dow’s Perspective “From EPA’s standpoint, clopyralid’s toxic profile is very, very good; the application rates of clopyralid used today are very, very low,” says Scott Eicher, senior marketing manager with Dow AgroSciences in Indianapolis, IN. “When clopyralid started appearing in compost, the first reaction from the solid waste industry was overreaction. If there was widespread plant death occurring, we would have heard more about it–but there’s not. We’re working directly with state and federal environmental protection agencies on this issue.”Dow AgroSciences is considering a number of changes in its clopyralid distribution. In April 2002, Dow and Riverdale Chemical Company notified EPA of changes to product labels that will prohibit future use on California residential lawns. Both companies have also requested that lawn-care operators, dealers, and distributors not sell or use clopyralid-containing herbicides on residential lawns in California.“We have to ask–what, if any, residential use should remain if clopyralid’s getting into compost? Of course, if more homeowners would use a mulching mower, there’d be no issue,” Eicher says. “Will a packaging-label change be enough? With the new guidelines we’re establishing, commercial applicators would have to inform homeowners about clopyralid.”Perhaps chemical testing processes, such as those that aid in developing Material Safety Data Sheets, need to adjust their focus. Studying a chemical’s effect from “cradle to grave” might not be enough, especially if the chemical never makes it to the “grave” and becomes recycled.“All this started around 1990, when states put in laws about ‘no organic in landfills,” Eicher explains. “Now it’s turned out that there’s no shortage of landfills. Some states have said, ‘We will recycle’–but the ramifications of that weren’t investigated. What we’re trying to do, from a stewardship standpoint, is–as much as possible–reduce the amount of clopyralid that could get into the composting stream. From a science standpoint, we’re trying to document when composters should have a concern about clopyralid levels. For one thing, they should test compost anyway to rid it of salt, immature compost, clopyralid, et cetera. Do a bioassay. If it’s revealed to contain clopyralid, do lab tests to find [out] how much. Bioassay can tell quickly and inexpensively if there’s a problem.”The Shape of Compost to Come?William Brinton concurs: “This is a wake-up call. We have to be more mindful of what’s going through the recycling chain. We need ‘cradle-to-cradle’ studies–substances are ‘born’ in one product, recycled, and born in another product. EPA didn’t think of this–it fell right through the cracks. At present, there’s not enough foresight being used on how we recycle things. We’re not passing laws to ensure quality of the product.“There’s a lot of pressure on every side,” he continues. “You can’t place blame on one company or one product; that’s not fair. I have often complained to the industry about compost maturity, but that [falls] on deaf ears.”Eicher agrees that a brief curing time might be part of the problem. “Is it compost, or is it just mulch? There are compost standards in Europe, but not here.”“The compost industry should put its best foot forward on this issue, and the chemical industry needs to too–by reducing chemical persistence in compost,” Brinton says. “Of course, the compost industry should aid in keeping chemicals out. How many composters grind up shipping pallets–stained with oil and grease–into compost? Another issue to be resolved: industry certifications are still voluntary. We at Woods End have started our own compost certification program. Rodale Press (publisher of Organic Gardening) is working with us on this. We want to become like the Underwriters Laboratory of compost.”