Modeling of degradation kinetic and toxicity evaluation of herbicides mixtures in water using the UV/H2O2 process.

The UV/H2O2 process was applied to the treatment of different mixtures of herbicides in water. Glyphosate, the herbicide most used in the world, was mixed with other hormonal herbicides with residual activity as 2,4-D and dicamba. The main goals of the study were to develop a kinetic model for interpreting the simultaneous oxidation of two mixtures (glyphosate plus 2,4-D and glyphosate plus dicamba). The model is based on a complete reaction mechanism, which comprises hydrogen peroxide photolysis and decomposition of both herbicides in each mixture studied. It takes into account the effect of non-uniform distribution of the local rate of absorbed photons. Good agreement of experimental data and the model is achieved in spite of differences in the reactivity between glyphosate and 2,4-D (or dicamba). Toxicity assays (employing Vibrio fischeri) were also performed, indicating that the toxicity of the mixture of glyphosate and 2,4-D was significantly reduced after the treatment.

Effectiveness evaluation of glyphosate oxidation employing the H(2)O(2)/UVC process: toxicity assays with Vibrio fischeri and Rhinella arenarum tadpoles.

The H(2)O(2)/UVC process was applied to the photodegradation of a commercial formulation of glyphosate in water. Two organisms (Vibrio fischeri bacteria and Rhinella arenarum tadpoles) were used to investigate the toxicity of glyphosate in samples M(1,) M(2), and M(3) following different photodegradation reaction times (120, 240 and 360 min, respectively) that had differing amounts of residual H(2)O(2). Subsamples of M(1), M(2), and M(3) were then used to create samples M(1,E), M(2,E) and M(3,E) in which the H(2)O(2) had been removed. Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities were measured in tadpoles to determine possible sub-lethal effects. In V. fischeri, M(1,E), which was collected early in the photodegradation process, caused 52% inhibition, while M(3,E), which was collected at the end of the photodegradation process, caused only 17% inhibition. Survival of tadpoles was 100% in samples M(2), M(3), and in M(1,E), M(2,E) and M(3,E). The lowest percentages of enzymatic inhibition were observed in samples without removal of H(2)O(2): 13.96% (AChE) and 16% (BChE) for M(2), and 24.12% (AChE) and 13.83% (BChE) for M(3). These results show the efficiency of the H(2)O(2)/UVC process in reducing the toxicity of water or wastewater polluted by commercial formulations of glyphosate. According to the ecotoxicity assays, the conditions corresponding to M(2) (11 ± 1 mg a.e. L(-1) glyphosate and 11 ± 1 mg L(-1) H(2)O(2)) could be used as a final point for glyphosate treatment with the H(2)O(2)/UV process.