LOS ANGELES — Traces of a herbicide toxic to garden vegetables has been found in compost in three states, a discovery that worried the lawn waste recycling industry.

Compost and recycling companies told the Los Angeles Times that their businesses could go bankrupt unless the herbicide is eliminated.

"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.

The small amounts of Clopyralid, which is produced by Dow AgroSciences, were found in compost made from recycled grass, straw, and manure in California, Washington, and Pennsylvania as well as New Zealand. The herbicide, used mainly to kill weeds, is not deadly to humans or animals, but it can kill vegetables such as peppers, tomatoes, and potatoes.

Clopyralid is used in dozens of products popular with crop farmers and commercial lawn-care companies.

Nationally, 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 California, nearly half the compost made from recycled garden clippings is used for agriculture.

Clopyralid kills plants by imitating hormones called auxins and causing abnormal growth. During commercial composting, most chemicals used in lawn care and agriculture break down completely enough to satisfy organic farmers, but Clopyralid survives the process. It can remain lethal up to 18 months after spraying.

Dow did not study the chemical's effects in compost when it originally sought federal approval in 1987. Seven years later, the company began putting warnings on the labels of Clopyralid products saying consumers should not compost materials treated with the herbicide. Dow spokesman Garry Hamlin said problems happened because Dow's label warnings were ignored. Material treated with the herbicide should have been disposed of another way but was recycled, he said.

Some areas are finding high levels of the herbicide in its compost. In Washington, Clopyralid residues are at rates of 50 to 1,500 parts per billion, five to 300 times higher than the amount needed to kill sensitive plants.

The chemical was first discovered in the soil around dying plants in 1999 in Spokane, Wash.

Dow products using the chemical include Lontrel, Transline, Stinger, Reclaim and Confront, Hornet, Scorpion, and Redeem. Other companies' pesticides that use Clopyralid bought from Dow include Millennium, Momentum, Chaser Ultra, Battleship, Strike Three, and TruPower.

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