Photodegradation of mecoprop and dichlorprop on dry, moist and amended soil surfaces exposed to sunlight

The effects of environmental conditions on the photodecomposition of two phenoxy-alkanoic acid herbicides were investigated on different soil surfaces conditions under sunlight exposition. A technique has been developed to study this process on moist nonsterile soil surfaces. A slow rate of disappeareance occurs in the three soils exposed to sunlight in absence of water. Photolysis of these herbicides is controlled by soil texture and its adsorption capacity. The organic matter does not have a sensitizing effect on the photodecomposition of these herbicides on dry soil surfaces. On nonsterile moist soil surfaces exposed to sunlight, the photolytic process prevails in the two first days of exposure and the transformation kinetics fits the Hoerl function better than the first-order exponential equation.