Research on controllable alkaline soil degradation of 5-substituted chlorsulfuron

Sulfonylurea (SU) has become one class of the most important herbicides worldwide due to their ultra-low application rate and mammalian toxicity. Recently application licenses of 3 classical SU herbicides chlorsulfuron, metsulfuron-methyl and ethametsulfuron were suspended due to their undesirable long persistence which is incompatible with the particular rotation planting system in China. Our previous study has discovered that electron-donating groups, especially dimethylamino and diethylamino substituents, on the 5th position of the benzene ring in chlorsulfuron, greatly accelerated its degradation rate in an acidic soil (pH 5.41). Owing to the natural slower degradation of SUs in alkaline soil, dimethylamino and diethylamino substituted chlorsulfuron Ia and Ib were further studied in an alkaline soil (pH 8.46) with chlorsulfuron as a control. The experimental data indicated that the half-life of degradation (DT50) of Ia was 3.36days while Ib was 6.25days which amounted to 30 and 15 folds faster than chlorsulfuron (DT50 84.53 days), respectively. The research confirmed that our newly-designed structures Ia and Ib can hasten their degradation rate in alkaline soil as well as in acidic soil. This structural modification of the classical SU provided an opportunity to control the degradation rate to reduce their impact on relevant environment and ecology.