Study on the photodegradation of glyphosate using UV/H2O2 process

C.S. ZALAZAR; A. MANASSERO; R.J. BRANDI; A.E. CASSANO

Palermo, Italia

Congreso; 5° European Meeting on Solar chemistry and photocatalysis: environmental applications (SPEA 5); 2008

“Schiavello-Grillone” Photocatalysis Group

Glyphosate (N-phosphonomethyl glycine) is a non-selective, post-emergence, broad-spectrum organophosphate herbicide, which is the most widely used herbicide in the world. In Argentina, over 13 million ha of arable land are dedicated to the production of transgenic, glyphosate-resistant (GR) soy and, together with Canada and the United States, contributes to most of the global acreage cultured with GR crops. Presently, Argentina is the second largest world producer of GR soy. This production has been accompanied by an increase in the use of glyphosate (over 60 million L between 1998 and 1999) 1. Thus, the substitution of traditional crops by GR soy within the last couple decades represents a large-scale, unplanned, ecological experiment, whose consequences for the natural ecosystems is poorly understood.       The United Nations estimates that of all pesticides used in agriculture, less than 1 % actually reaches the crops. The remainder ends up contaminating the land, air and, mainly, water. Only a small amount of the waste is presently treated due to the lack of available on-site treatment technologies. Thus, under these circumstances,   Advanced Oxidation Technologies seem to be a potential choice to decrease glyphosate concentrations within admissible limits, particularly because complete mineralization is always achieved. Chen et al.2 and Shifu and Yunzhang3 have studied the photodegradation of glyphosate in aqueous solution in the ferrioxalate system and employing TiO2 respectively.  In both studies the glyphosate was easily degraded.     The combination of hydrogen peroxide and UV radiation should be a suitable process for treating this type of pollutants. This work was planned with two specific purposes: (i) to know the best operating conditions for the complete degradation of glyphosate using UVC radiation (253.7 nm); particularly, to know the optimal pH and the optimal ratio of hydrogen peroxide to glyphosate concentrations for degradation and (ii) to propose a plausible reaction sequence for developing a future kinetic model.