Summer, 1996 (v8n3)
F.C. Michel Jr., D. Graeber, L.J. Forney and C.A. Reddy
Biocycle 37(3):64-66. 1996
This article presents the results of a study that has relevance to farmers and gardeners wishing to use compost from lawn clippings that may have been treated with pesticides. According to the article, over 30,000 tons of pesticides are used each year on lawns, turf farms, and gardens in the U.S.
In this study, researchers determined the fate of three lawn care pesticides during composting. The pesticides tested were the insecticide diazinon, which is the most widely used lawn care pesticide in the U.S.; 2,4-D, a postemergence broadleaf herbicide which ranks second in use; and pendimethalin (also called Prowl®), a preemergence herbicide commonly used to control broadleaf and grassy weeds. The experiment was conducted using a laboratory scale compost system which simulates the temperature and aeration conditions found in windrows. The sample yard trimmings consisted of leaves and grass in a 2:1 ratio (wet weight basis). This blend was amended with radioactive pesticides at 10 ppm, to simulate the levels of these compounds that might be expected in raw materials used at composting facilities.
Each pesticide was tested for three fates. The most desirable fate for a pesticide during composting is complete mineralization to carbon dioxide (CO2). Another potential fate is volatilization into the atmosphere, which may be accelerated by high composting temperatures. Pesticides could also be leached out during composting and contaminate groundwater.
The results showed that 2,4-D was mineralized relatively rapidly during composting, with nearly half converted to CO2 in 50 days. Also, the rate of mineralization paralleled the rate of conversion of total carbon (in the yard trimmings) to CO2. Diazinon and pendimethalin mineralized much more slowly. Only small fractions of the three pesticides were volatilized, even though the temperature was maintained at 55 to 60 C (131 to 140 F) through much of the composting period. The leachability of each of these pesticides was also low. Finally, only a small portion of the pesticides remained unchanged in the final compost: less than 0.01 ppm for 2,4-D, 0.01 ppm for diazinon, and 0.1 ppm for pendimethalin.
This study also evaluated the quantity of pesticide breakdown products in the compost. Nearly 30 percent of the diazinon originally present in the feedstock was found to be rapidly converted to a substance with low toxicity. On the other hand, very small amounts of breakdown products from pendimethalin and 2,4-D were found.
Researchers also studied the fate of carbon in the three pesticides during composting. The results showed that while most of the carbon was extractable when composting began, about half of the 2,4-D and diazinon carbon and about three-fourths of the pendimethalin carbon was found in humic materials or was unextractable from the final compost. This pesticide carbon was believed to be chemically different from the parent compound and less bioavailable than the original pesticide. It was noted, however, that very little is known about how, and in what form, these "bound" pesticide residues in compost are released over time.
For more information contact: Michel Graeber, NSF-Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48825.
(CI-PEST.138)
Contributed by Chuck Ingels
[ Back | Search | Feedback ]