Herbicide Contamination of Feedstocks and Compost at or below Practical Analytical Detection Limits

摘要

Composting is an excellent method to recycle organic materials due to its sanitizing effect on weeds, disease organisms, and pesticides. Unfortunately, composts made from feed stocks treated with some persistent herbicides may retain phyotoxic levelsinjurious to plants. Clopyralid, detected in compost in the US and in some foreign countries, is extremely toxic to some legumes, tomatoes, potatoes and sunflower at levels of 10 parts per billion (ppb) or less. Produced by Dow AgroSciences, clopyralid is a chlorinated pyridinecarboxylate that functions as a plant growth regulator. It is the active ingredient in over 30 products including Confront, Curtail and Stinger and is used to control annual and perennial weeds in crop production and in turf. Typical symptoms include leaf cupping, loss of apical dominance, failure of trifoliate leaves to develop, and prevention of fruit set. Clopyralid-contaminated compost from grass clippings was noted in 1999 at nurseries in Spokane WA, in 2000 at PennsylvaniaState University, and in 2001 at Washington State University from grass hay. Since, numerous instances of clopyralid contamination have been reported in compost in the US and in New Zealand. Because of the relatively high tolerance allowed for clopyralid, most laboratories do not routinely measure clopyralid below 50 ppb and injurious levels may not be detected. Studies are underway to further identify composting conditions and management options to enhance herbicide breakdown. Recommendation/conclusions are: 1) Bioassay all feed stocks and compost for symptoms and verify with analytical tests; 2) become familiar with feedstocks sources and inquire whether persistence herbicides have been used; 3) re-examine the criteria when considering the registration and re-registration of persistent herbicides to include all possible end users of plant residuals; 4) re-examine the chemistry and formulation of existing and new herbicides for persistence in the environment so that the recycling and composting industries and municipalities are not at risk.