Compost Contamination Tests Inconclusive
08/23/12 7:34AM By John Dillon
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The results have frustrated state and local officials, who had hoped to have more answers by now about what's caused some commercial compost to damage garden plants.
Agriculture Secretary Chuck Ross says the tests on compost chemistry done for the state didn't validate earlier lab results ordered by the Chittenden Solid Waste District.
The tests for the solid waste district showed trace amounts of two persistent herbicides, Picloram and Clopyralid.
But four samples of the same compost tested for the state did not show those chemicals. Instead, a third herbicide was found. Ross says the conflicting results raise more questions than answers.
"So I am worried, but I'm not convinced that this is not a manageable problem yet," he says. "But we've got to get through the investigation. And it's perplexing and frustrating that we have two very good labs, two national labs, coming up with different results."
The problem was seen earlier this summer in compost sold by the Chittenden Solid Waste District.
Investigators believe trace amounts of herbicides stunted growth and wilted leaves in broad leaf plants such as tomatoes and beans. The district halted sales of its compost. It's spending about $1 million to study the issue and compensate gardeners for their losses.
The state Health Department says the levels are too low to affect human health.
Still, waste district manager Tom Moreau is deeply frustrated. He wants the U.S. Environmental Protection Agency to implement a national standard for testing. Moreau says the testing methods his agency and the state have to rely on are proprietary - meaning they are owned by the companies involved.
"Isn't it funny that the state has to call DuPont and Dow saying, ‘How do you test for these compounds?'" Moreau asks. "Sure, they're the authors and they're the originators and they're the patent holders of those. But, don't you think that when they're registered, that we would have a universal methodology to test for them in residuals?"
The waste district has hired a consulting chemist to help with the science. And the science is challenging and expensive.
Moreau says it's particularly difficult to find and isolate chemicals at levels of parts per billion in substances like compost and manure that have many different chemicals and biological interactions.
Moreau says he stands by the results from the lab he hired, an Idaho firm called Anatek. The lab found trace levels of herbicides not only in the district's compost but also in horse manure, animal feed sold by major feed companies, and other compost products in Vermont.
"So we're basically saying to the state of Vermont: ‘This is what our investigation shows us. It's your investigation. We don't have investigative authorities. Please tell us where you find it. Trace it up,'" he says. "In the meantime, we're going to continue to use Anatek and believe their results."
Moreau says the district also plans to conduct its own greenhouse grow tests using compost made from various feedstocks to see the effects on plants.
Read Persistent Herbicide FAQs from Chittenden Solid Waste District here.