DEGRADATION OF AQUEOUS ATRAZINE AND METAZACHLOR SOLUTIONS BY UV AND UV/H2O2 - INFLUENCE OF PH AND HERBICIDE CONCENTRATION

The degradation of two pesticides: atrazine and metazachlor was investigated in aqueous solution under UV-irradiation with and without H2O2. Rate constants of the photochemical degradation were determined applying a first order kinetics and quantum yields of the processes were calculated. This approach leads to an apparent decrease of the quantum yield with increasing initial pesticide concentration. At low H2O2 initial concentrations, the pesticide degradation was shown to be much more efficient than the degradation under UV-irradiation only. However, at high H2O2 concentrations (>2 mmol L-1), the efficiency of the UV/H2O2 system dropped down and the quantum yields of degradation were lower than for the direct photolysis. In the absence of H2O2, no influence of the pH value on the photodegradation of the pesticides could be noticed in a range between pH 3 and pH 11. At low H2O2 initial concentrations, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH 11. The results emphasize the potential of optimized reaction conditions in advanced oxidation.