Penn State Research Uncovers Clopyralid In Compost

From BioCycle
Journal of Composting &Organics Recycling
July 2001, Page 32

TIMELINE FOR CHEMICAL LONGEVITY
PENN STATE RESEARCH UNCOVERS CLOPYRALID IN COMPOST
University studies identify grass as major culprit, while growth trials continue using tainted compost.
Nadine J. Houck and Eric P. Burkhart

IN SPRING, 1997, staff at Penn State University began composting under the direction of the Organic Materials Processing and Education Center (OMPEC) — a collective effort of the College of Agricultural Sciences, Housing and Food Services and Operation of Physical Plant with a mission to curb the campus waste stream. At Penn State, feedstocks include campus landscape debris, preconsumer dining commons food residuals and dairy manure. These are generated within the university, and composted in windrows to produce a finished product that is largely utilized in campus landscaping.

In the spring of 2000, compost generated from this program began to be used for vegetable crops research. This was the first time the compost was used on food crops; previously all applications had been made to ornamental beds. The goal of the study was to characterize the performance of vegetable crops following two application rates: 632 gallons per 612 square feet (about 1.5 inches applied to the soil surface and incorporated) and 1,264 gallons per 612 square feet (about 3.0 inches). The rates were chosen using the nutrient profile of the finished product, along with projected crop needs. A second motive was to evaluate published recommendations.

The first crop to be grown in the study was bell peppers. Nearly four weeks after transplanting, the plants began to exhibit abnormalities resembling those caused by a phenoxy acetic-acid herbicide such as 2, 4-D. These symptoms included leaf cupping and strapping and were most apparent in the new growth (i.e. apical meristem). Drift from nearby field plots was initially suspected but was ruled out when no clear source could be established. Continued investigation failed to conclusively tie the distorted appearance of the plants to other environmental and physiological cropping factors. Distorted growth and fruit persisted into the fall, though with less severity.

Samples of the compost used in the bell pepper trials were eventually submitted to a laboratory — the same used by Washington State University — to be tested for the presence of 2, 4-D, dicamba, clopyralid, triclopyr, and picloram. Initial testing indicated clopyralid residue between 17 and 31 parts per billion (ppb) and no detectable residues were found for 2, 4-D, dicamba, triclopyr or picloram. The compost with the lowest level of residue was approximately one year old and had been exposed to rain and snow. The samples with the higher levels of residue were collected from windrows immediately prior to curing. Additional testing has found residue levels in finished compost ranging from 10 to 75 ppb.

IDENTIFYING THE SOURCE

After identifying the possible contaminant, investigation turned to determining the source. Since all compost feedstocks are produced within the university system, the potential sources were identified as the dairy manure and/or the leaves. Initially the Dairy Center and Farm Operations were contacted to determine if herbicides containing clopyralid were used in production agricultural practices. It was established that the University’s agricultural practices did not include the application of clopyralid. However, it could not be determined if purchased hay had products applied containing clopyralid. In addition, herbicide products containing clopyralid, Confront and Millennium, were identified as being used on campus to control broadleaf weeds in turf.

The two possible sources seemed to be manure or landscape debris. It was puzzling because the only landscape debris used in the composting process is leaves. Further testing of manure and leaves revealed no detection in the manure and the residue in leaves ranged from no detection up to 354 ppb. The carrier of the contamination appeared to be the leaves, but it was still a mystery as to how the leaves could be the source. These factors were identified: Over-spray from turf applications; Translocation; and/or Minimal grass collected when the leaves were vacuumed. Additional samples of leaves were collected but before being analyzed, the grass was separated from the leaves and tested individually. Grass comprised less than one percent of the samples by weight. The grass contained clopyralid residue of 573 ppb and the leaves contained 36 ppb, which suggested that the grass, and not the leaves, was the culprit.

In an effort to determine if clopyralid could be translocated through the tree’s vascular system, several samples of new leaf growth were tested. The samples were taken from oak, maple and elm trees. Results indicated no detection of clopyralid. However, these findings are tempered by the fact that there is a minimum detection level of 1 ppb; the leaves may actually contain less than this amount.

HERBICIDES STOPPED, COMPOSTING CONTINUES

Since discovering the herbicide residue, Penn State has ceased using Confront and Millennium for turf applications. The finished compost in inventory is being utilized in turf applications as a topdressing. Composting is Penn State’s method of managing leaves. The leaves in inventory are being composted intensively with manure and will also be applied to turf. Currently compost for ornamentals is being made with switch grass and soybean fodder.

Despite the widespread contamination, vegetable crop growing trials continue using tainted compost. One reason is so the phenomenon can be carefully documented in order to develop identification and remediation recommendations for vegetable growers. In 2001, contaminated compost has been used in the production of leafy greens, culinary herbs, and onions. In addition, the bell pepper study initiated in 2000 is in its second year. Already the latter study is revealing that, given certain conditions, clopyralid can persist for more than two years after application and incorporation into the soil. It is anticipated that such findings will help to establish a timeline for chemical longevity and remediation.

Perhaps one of the most significant observations in the Penn State growing trials is that symptoms are often not expressed until about four weeks after transplanting from greenhouse to field, which raises questions regarding the value of short-term bioassays for detection. Much appears to depend on the nature and extent of contamination. For example, researchers at Washington State University (WSU) found that with high levels of contamination, plants grown using bioassays can show symptoms within days (see article, this issue). At Penn State, symptoms have generally not been as quick to develop, even given contamination levels as high as 74.5 ppb. The reasons for these differences in expression time are still not fully understood but may be at least partially related to moisture conditions. According to Mary Fauci, research technician at WSU, "wet/dry cycles seem to release more herbicide from contaminated compost than constantly wet conditions." The vegetable growing trials at Penn State have occurred under controlled cropping conditions, with use of drip irrigation and plastic mulch. Given the high water solubility of clopyralid, there is reason to suspect that irrigation methods and frequency may play a role in the uptake, and eventual expression, of herbicide toxicity. Clearly more research is needed as to how cropping circumstances influence herbicide release.

Nadine Houck is the Composting Coordinator with the Agricultural and Biological Engineering Department at Penn State University. Eric Burkhart is a Research Assistant with the Department of Horticulture.

BIOCYCLE | IN BUSINESS | COMPOST SCIENCE |

HOME