Residue from a herbicide deadly to several common vegetables has turned up in compost from San Diego to Seattle, threatening the rapidly growing composting industry and the urban waste disposal projects that depend on it.
Traces of Clopyralid, manufactured by Dow AgroSciences and toxic to vegetables such as potatoes, peppers, tomatoes and beans, have been found in compost made from recycled grass, straw and manure in California, Washington state, Pennsylvania and New Zealand.
The herbicide, most commonly used to kill backyard dandelions and field thistles, is not toxic to humans or other mammals. But it causes garden vegetables to wither and die.
Widely used on lawns and wheat crops, the chemical has found its way into compost through grass clippings, stable sweepings and manure.
Compost companies and recycling officials say that if the contamination persists, it could bankrupt the industry. That, in turn, could divert more than a quarter of California's waste stream back to landfills, busting landfill quotas and triggering fines for cities and county governments.
In California, which has the most ambitious green-waste recycling standards in the country, composting projects have diverted nearly one-third of the waste bound for landfills.
Around the country, compost companies accept about 28 million tons of yard trimmings each year. The material comes from more than 9,700 curbside collection programs run by city and county sanitation departments in 37 states.
In Washington, sample testing around the state is finding Clopyralid residues at rates from 50 to 1,500 parts per billion, five to 300 times higher than the amount needed to kill sensitive plants.
The chemical was first detected in the soil around dying plants in Spokane, Wash., in 1999 and a year later in Pullman. In the first sign of it in California, San Diego's Environmental Services Department, which recycles 85,000 tons of garden clippings a year, got a positive test in June from compost it produced.
City sanitation officials in San Diego and Seattle, along with the U.S. Composting Council, an industry group, are calling for the removal of Clopyralid from lawn care products. "We feel that potentially all of our [landfill] diversion is at risk because of this product," said Stephen Grealy, the recycling program supervisor for San Diego.
"You cannot have a system that mandates recycling of green waste, and license a garden chemical that makes the waste unrecyclable," said Gabriella Uhlar-Heffner, solid waste manager for Seattle's public utility company.
Dow officials say the company did not study the chemical's behavior in compost when it originally sought permission to market it in 1987. In 1994, the company began putting warnings on the labels of Clopyralid products saying consumers should not compost materials treated with the herbicide, a company spokesman said.
The current problems arose because Dow's label warnings were ignored, said Dow spokesman Garry Hamlin. Material treated with the herbicide should have been disposed of another way but was recycled, he said.
But San Diego officials responded that the warning "is obscure enough to confuse any reasonable applicator."
The modern garden-waste recycling industry arose after a 1988 federal clampdown on landfill standards forced states to substantially reduce the amount of waste sent to landfills.
California led the way. In 1989, the state passed legislation requiring every city and county to divert 50% of its waste from landfills by 2000 or face penalties as high as $10,000 a day.
Los Angeles has exceeded the quota with "about 55%" diversion from landfills, said Stephen Fortune, principal sanitary engineer with the Bureau of Sanitation.
Fortune attributed the program's success to a curbside collection system that picks up about 2,000 tons of yard trimmings a day.
Once collected, the garden clippings are broken down into compost. The process mimics natural decay on a forest floor, but at temperatures between 100 and 150 degrees and on an industrial scale of tens of thousands of tons a year. Unlike Clopyralid, which survives the heat, most chemicals used in lawn care and agriculture break down completely enough to satisfy organic farmers.
In California, almost half the compost made from recycled garden clippings goes to agriculture and 37% to horticulture. A contaminated product, composters fear, would bring these sales to a standstill.
The launch of Clopyralid preceded the composting movement. Formulations involving it were first registered in 1987 as products to control broadleaf weeds such as dandelions and thistles. It was then approved for use on barley, oats, wheat, sugar beets, Christmas trees, corn, mint and asparagus, as well as for treatment of range land, pasture, highway aprons and lawns.