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 invest igated in aqueous solution under UV-irradiation with and without H2O2. Rate constants of the photochemical degradation were determined apply ing a first order kinetics and quantum yields of the processes were ca lculated. This approach leads to an apparent decrease of the quantum y ield with increasing initial pesticide concentration. At low H2O2 init ial concentrations, the pesticide degradation was shown to be much mor e efficient than the degradation under UV-irradiation only. However, a t high H2O2 concentrations (>2 mmol L-1), the efficiency of the UV/H2O 2 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 not iced in a range between pH 3 and pH 11. At low H2O2 initial concentrat ions, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH 11. The results e mphasize the potential of optimized reaction conditions in advanced ox idation.