Hydrolysis of Azadirachtin in Buffered and Natural Waters

Abstract

The hydrolysis of azadirachtin was studied in several aqueous buffers of pH 4.1−8.1 and in four natural waters (pH 6.2, 7.3, 8.0, and 8.1) at 20−45 °C. Depending on the pH, several unidentified conversion products were detected in the incubated solutions. Azadirachtin hydrolyzed readily at 35 °C, and its disappearance followed simple pseudo-first-order kinetics. The rate constants ranged from 2.48 × 10-3 to 67.7 × 10-3 h-1 and were faster in basic than in acidic pH. On the basis of calculations from the Arrhenius plot, the energy of activation and the frequency factor A for the hydrolysis of azadirachtin at pH 7.0 were 103 kJ mol-1 and 2.51 × 1015 h-1, respectively. On the basis of rate constants, azadirachtin appeared to be more susceptible to hydrolysis than synthetic organophosphates, e.g., chlorpyrifos, diazinon, malathion, parathion, and Ronnel, or carbamates, e.g., carbaryl and propoxur. All of these insecticides are currently used extensively for pest control. Accordingly, azadirachtin is expected to be nonpersistent in water. Keywords: Azadirachtin; hydrolysis; kinetics; aqueous solutions