STATEWIDE SAMPLING
OREGON COMPLETES CLOPYRALID STUDY
A recent study determined that clopyralid is present in Oregon compost and highlights how different testing protocols yield differences in concentrations.
Robert Rynk

EVER since the herbicide clopyralid was detected in composts in Washington, composters in Oregon have been anxious about the prospects of finding clopyralid in compost produced in their state. To learn whether clopyralid was in fact an issue, in 2002 the Oregon Department of Environmental Quality (DEQ) conducted a search for residues of the herbicide in compost produced at DEQ-permitted facilities. Results of the study were recently released and summarized in a fact sheet issued by the agency. The study determined that clopyralid is present in Oregon compost, and at levels that merit attention. The study also found generally higher levels in samples taken in October compared to June, and differences in concentrations based upon testing protocols.

A QUICK CLOPYRALID REVIEW

Clopyralid is an herbicide that is effective on a variety of weeds and is damaging to sensitive plants at very low concentrations — down to, and sometimes below, 10 parts per billion (ppb) in the growing media of the plants (e.g. soil). The problem is this group of sensitive plants includes popular agricultural and garden crops like tomatoes, peppers, potatoes, peas, beans, clover, alfalfa and sunflower.

BioCycle has provided thorough coverage and analysis of clopyralid research and findings since the issue first arose. (Search the BioCycle archives — http://pqasb.pqarchiver.com/jgpress/ — for a complete list of articles.) In 2000, damage to plants grown in compost, and compost amended soils, was linked to residues of clopyralid in the composts (a similar herbicide, picloram, was also implicated in one case). The initial incidents occurred in eastern Washington. However, subsequent statewide testing by the Washington State Department of Agriculture (WSDA) found that clopyralid was present at potentially damaging levels in composts produced throughout the state. The herbicide has since been identified at potentially damaging concentrations in a dozen widely dispersed states. However, Washington still can claim the greatest number of compost products sampled and the highest concentrations. Although clopyralid does decompose, it has been suggested, although not confirmed, that it persists longer in composting situations than in soils. Nevertheless, even with substantial decomposition, there may still be enough clopyralid left to injure plants where compost is used simply because it has an impact at such low concentrations.

Clopyralid can arrive at a composting facility in a variety of feedstocks including grass clippings, mixed yard trimmings, straw, manure and other agricultural residues. However, grass clippings have been the feedstock of focus because clopyralid is a commonly used herbicide on lawns and because grass clippings are frequently taken to composting facilities.

The threat that clopyralid presents to the composting industry, and organics recycling generally, has led to restrictions in several areas. WSDA banned the use of clopyralid for all turf applications except parks and golf courses (if clippings are not sent to a composting facility). Dow AgroSciences, the herbicide’s manufacturer, proposed changing the label to prohibit its use on residential lawns. California recently passed legislation that calls for a study of the herbicide’s impact on the compost industry and then appropriate restrictions if negative impacts are possible.

THE OREGON STUDY

To help guide its study, the Oregon DEQ assembled a task force of specialists from DEQ, the Department of Agriculture (ODA), Metro Regional Government and the Composting Council of Oregon. To review the lab results, DEQ relied on pesticide, weed and compost experts from these agencies and Oregon State University. The study gathered samples of ready-for-sale compost from 12 compost facilities permitted by DEQ (36 facilities are permitted in Oregon). The 12 facilities that provided samples are located throughout Oregon and predominantly compost yard trimmings in windrows or passive piles.

For each facility, the samples tested for clopyralid were drawn from a composite of multiple samples, collected on site and then mixed together. Theses samples were analyzed for clopyralid concentrations by analytical laboratories and bioassays conducted by a seed germination laboratory. The study took place in two phases. Phase I samples were collected in June 2002; Phase II samples in October. Phase I samples were sent to one commercial analytical lab (Lab A). For analysis, Lab A used a modification of an EPA approved method (EPA Method 8151A) that is common for quantifying herbicide concentrations. In Phase II, samples were sent to Lab A and a second commercial laboratory (Lab B), which used a slightly different analytical procedure. The DEQ fact sheet refers to this procedure as the “GC/MS” method (see sidebar).

The bioassay tests involved growing peas, beans and clover seeds in a 50:50 volume mix of compost and peat moss. For the positive control tests, the seeds were planted in compost/potting soil mixtures that were known to contain clopyralid. The negative controls included potting mix only and potting mix plus compost amended with activated charcoal to bind the clopyralid. The plants were grown for 20 days. Afterwards they were photographed, visually examined and assigned a numerical score for severity of the observed herbicide damage (e.g. leaf curling). For the purpose of this study, any sample with a visual score greater than zero (i.e. no damage) failed the bioassay. Thus, any sign of damage on the 21st day resulted in a “fails” rating.

Results from the study are summarized in Table 1. In Phase I, clopyralid was found in samples from one-third of the composting facilities at levels ranging from 7.6 to 38 ppb (Lab A). Although clopyralid was probably detected in most of the samples, the laboratory was unable to positively confirm it (see footnotes in Table 1). In Phase II, clopyralid was detected in nine of the 12 samples analyzed by Lab A (range 8.3 to 49 ppb). Lab B found that all of the samples contained clopyralid at levels ranging from 6.3 to 94 ppb. The method used by Lab B consistently indicated higher levels than the Lab A method (see sidebar). The greater prevalence of clopyralid in the Phase II samples is likely due to timing. The Phase II samples were collected in October from compost that was manufactured from yard trimmings brought to the facilities in the summer, with a higher proportion of grass clippings and more recent applications of the herbicide.

The bioassay results were consistent with the analytical tests. With only one exception, where clopyralid was detected in analytical tests, bioassays yielded a “fails” rating. The one exception occurred with a sample that found clopyralid at a concentration of 6.3 ppb by the “GC/MS” method. The bioassay control tests were predictable. Plants in the positive controls failed the bioassay while those in the negative controls passed.

WHAT DOES IT ALL MEAN?

The study demonstrates that clopyralid is a factor for the Oregon composting industry. Although that fact should not come as a big surprise, at least it is now official. Generally, the levels of clopyralid found during the study are not extreme but they are high enough to merit caution when using the compost. Compost producers can now sell compost with a little more confidence and advise customers about appropriate use of compost given that clopyralid may be present. Marti Roberts-Pillon, with Oregon DEQ, feels that the study was a necessary step toward resolving the clopyralid issue. “With the news about clopyralid from Washington, composters in Oregon were in a difficult position,” she explains. “Should an individual compost producer test for clopyralid or not? And what should they do if they found it when other composters were not testing at all? DEQ considered this as an industry-wide issue. Therefore, by conducting this study we took much of the burden off of individual producers. This type of survey needs to be done by each state, or on a national level, because compost facilities cannot assess the seriousness of the problem alone.”

DEQ is making the results available to compost producers and users, pesticide applicators and distributors, EPA and other regulatory agencies for their consideration and response. The composting industry is expected to respond with an educational effort about clopyralid targeted to both feedstock generators and compost users. In addition, ODA now has data to evaluate what steps should be taken to reduce the potential for clopyralid to contaminate compost and affect nontarget plants in general. As the DEQ fact sheet states “the goal of these efforts is to ensure that material coming into compost facilities in the Spring and Summer of 2003 will not include clopyralid-treated materials.”

For more information about the DEQ study and other composting information, refer to the DEQ web site: www.deq.state.or.us/wmc/solwaste/composting.html. Or contact Marti Roberts-Pillon at Roberts-pillon.martine@deq.state.or.us.