ASSESSMENT OF CYANAZINE PERSISTENCE IN WATER

Cyanazine ,3,5,-triazin-2-yl]-amino]-2-methylpropanenitrile) is an imp ortant selective herbicide used for the control of several annual gras sy weeds and certain broad-leafed weeds in fields of corn, soybeans, a nd triazine-resistant canola. It is one of the most heavily used agric ultural herbicides in Ontario. There is, however, very little informat ion in the open literature on the aquatic fate and persistence of cyan azine, a fact that hinders the assessment of its ultimate impact on th e aquatic ecosystem. This research showed that cyanazine was very stab le in natural surface runoff and soil leachate. It was also very resis tant to microbial degradation in water under both aerobic and anaerobi c conditions. No apparent biodegradation or biotransformation of cyana zine was observed in a test using mixed cocktails of farmland runoff a nd soil leachate after an incubation period of 98 days. Its biological persistence was further demonstrated by a cyclone fermenter study in which cyanazine was found to be totally immune to the biodegradation p otential of a polynuclear aromatic hydrocarbon degrading bacterial cul ture and sewage microorganisms after an incubation period of 110-195 d ays. Using the herbicide metolachlor as a biodegradability reference c ompound and the white rot fungus Phanerochaete chrysosporium as the te st organism, cyanazine was estimated to have a persistence in water mu ch greater than that of metolachlor. Thus, the extensive herbicidal us e of cyanazine may have a long-lasting impact on Canadian aquatic ecos ystems. (C) 1996 by John Wiley & Sons, Inc.