PULLMAN, Wash. — Washington State University is investigating suspicions that some of its compost may be implicated in damage to garden plants in Eastern Washington and Northern Idaho.
Vegetables grown in soil treated with the compost are safe to eat, according to Alan Felsot, a WSU environmental toxicology expert.
James Zuiches, dean of the College of Agriculture and Home Economics, has confirmed that a complaint has been filed with the Washington State Department of Agriculture.
“A WSDA inspector has visited our composting operation,” Zuiches said. “We turned over our records and all pertinent information, including laboratory data and correspondence with concerned citizens,” Zuiches said.
Dan Caldwell, WSU farm and compost manager, said WSDA sampled WSU compost for review in their own lab. Caldwell gave WSDA photographs he took of injured plants.
When he received complaints that WSU compost might be implicated in injury to garden plants Caldwell sent samples to the University of Idaho Holm Research Center, and to Anatek Labs, Inc., both in Moscow, Idaho. WSU’s crop and soil sciences department also is conducting bioassays.
Because of the nature of damage to plants, plant growth regulators containing clopyralid or picloram are suspected. Caldwell said clopyralid is found in Confront and Curtail, which are long-lasting herbicides used to control broadleaf weeds. Confront is used on turf, and Curtail in agricultural settings to eradicate thistle. Picloram is found in Tordon, which also is used to eradicate thistle.
Caldwell said labs that tested samples only have the capacity to detect these compounds down to .05 parts per million, a level that a Dow Chemical representative and Felsot say is below the level of concern for human consumption. Felsot said the human body doesn’t metabolize the chemicals, but simply disposes of them by excretion.
However, toxicity can occur in some plant families at levels down to .01 parts per billion. Tomatoes, tobacco, beans, peas and potatoes are among the most sensitive. Corn, carrots and radishes don’t appear to be affected.
If the herbicides found their way into WSU compost, the logical route would be through feed fed to livestock. Caldwell said records turned over to WSDA should allow investigators to trace sources from material used to make the compost.
He said WSDA said it may take at least another month for it to reach conclusions.
Confront, Curtail and Tordon labels caution that it should not be used on materials that will be composted.
Caldwell said compost isn’t a soil and shouldn’t be used as a growing medium. It is a soil amendment. Adding it to the soil at a rate of more than 15 percent could cause plant damage because it ties up nutrients.
A recommended garden application would be to put about half an inch of compost on top of the soil and incorporate it. Applying too much compost may cause phytotoxic damage similar to that caused by the herbicide.
WSU’s award-winning composting operation began in October 1994 and has garnered international interest. WSU produces 12,000 cubic yards of compost a year, from about 24,000 cubic yards of organic material. Six thousand to 8,000 cubic yards of the compost is sold wholesale to nurseries, greenhouses, garden stores and landscapers. The rest is used by WSU.
Caldwell said WSU compost is marketed only in Whitman County in Washington and in Latah County and the Sandpoint and Coeur d’Alene areas in Idaho.
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