EFFECTS OF PH AND ADJUVANTS ON CLETHODIM PHOTODEGRADATION

Physical degradation of clethodim [2-[1-[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2- (ethylthio)propyl]cyclohexane-1,3-dione] occurred in aqueous solution by acid catalysis and photoca talysis in in vitro experiments as assayed by HPLC. Clethodim degradation increased as acidity increased, being further accelerated under UV light with a half-life of 2.4, 2.6, and 3.2 h at pH 5, 6, and 7, respectively. Fewer degradation products were formed under UV plus adjuvant treatments, but the rate of photodegradation was increased by 2- to 7-fold over the UV control. The degradation rate in sunlight plus adjuvant treatments was enhanced by 7- to 27-fold over the sunlight control. The photodegradation rates in the presence of adjuvants followed the sequence LI700 > Dash > Agrioil > XE1167 > CC15943 > control. In summary, clethodim degradation was catalyzed by acid, the rate being accelerated in light (probably a different mechanism), and was further enhanced by the addition of adjuvants to the light treatment. © 1990, American Chemical Society. All rights reserved.