Effects of moisture, temperature, and biological activity on the degradation of isoxaflutole in soil

The effects of several environmental factors on the dissipation, transformation and mineralization of isoxaflutole were investigated in laboratory incubations In the soil, isoxaflutole hydrolyzed to a diketonitrile derivative, which is the active form of the herbicide The diketonitrile was then metabolized to an inactive benzoic acid derivative and later into two unknown products which were found only in small quantities Degradation of isoxaflutole was faster in soil maintained at -100 or -1500 kPa compared to that in air-dry soil At 25 degreesC the half lives for isoxaflutole were 9 6 2 4, and 1 5 days in air dry -1500 kPa, and -100 kPa moisture regimes, respectively A simple Arrhenius expression described the response of isoxaflutole transformation (mineralization and transformation) to temperature in the range of 5 to 35 degreesC An activation energy value (E-a) of 67 kJ/mol for isoxaflutole suggested the transformation of the herbicide to the diketonitrile derivative was primarily a chemical reaction Moreover biological activity had little effect on the hydrolysis of isoxaflutole with half lives of 1 8 and 1 4 days in sterile and nonsterile soil respectively However the transformation of diketonitrile to benzoic acid and the production of the unknown products were greatly reduced in the sterile soil suggesting one or more biologically mediated processes.