Dissolution kinetics of copper oxide nanoparticles in presence of glyphosate

Recently CuO nanoparticles (n-CuO) have been proposed as an alternative method to deliver a Cu-based pesticide for controlling fungal infestations. With the concomitant use of glyphosate as an herbicide, the interactions between n-CuO and this strong ligand need to be assessed. We investigated the dissolution kinetics of n-CuO and bulk-CuO (b-CuO) particles in the presence of a commercial glyphosate product and compared it to oxalate, a natural ligand present in soil water. We performed experiments at concentration levels representative of the conditions under which n-CuO and glyphosate would be used (-0.9 mg/L n-CuO and 50 mu M of glyphosate). As tenorite (CuO) dissolution kinetics are known to be surface controlled, we determined that at pH 6.5, T - 20 C, using KNO3 as background electrolyte, the presence of glyphosate leads to a dissolution rate of 9.3 +/- 0.7 x 10(-3) h(-1). In contrast, in absence of glyphosate, and under the same conditions, it is 2 orders of magnitude less: 8.9 +/- 3.6 x 10(-5) h(-1). In a more complex multi-electrolyte aqueous solution the same effect is observed; glyphosate promotes the dissolution rates of n-CuO and b-CuO within the first 10 h of reaction by a factor of -2 to -15. In the simple KNO3 electrolyte, oxalate leads to dissolution rates of CuO about two times faster than glyphosate. However, the kinetic rates within the first 10 h of reaction are about the same for the two ligands when the reaction takes place in the multi-electrolyte solution as oxalate is mostly bound to Ca2+ and Mg2+.