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The reactivity of singlet oxygen (02('Ag)) with edta and its metal complexes with A13+, Cu2+, Fe3+, and Mn2+ was investigated. The emission of singlet oxygen at 1270 nm in D,O was measured in order to determine the quenching efficiency of edta and edta-metal complexes for different metal/edta ratios. The sum of the rate constants (kr + kq) of the chemical reaction between singlet oxygen and the acceptor (k,) and of the physical quenching of singlet oxygen by the acceptor (k,) was obtained by a Stern-Volmer analysis. Measurements of the oxygen consumption in H 2 0 were used to determine quantum yields of the sensitized photooxidation, and the combined results of these experiments allowed the determination of k, and k, separately. A strong isotope effect was observed between the deuterated and the hydrogenated solvents. This effect was shown to be independent of the analytical procedure used. The isotope effect, as well as the reactivity of edta and its metal complexes, depend markedly on the complexed metal ion.

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Summary: The degradation of two pesticides: atrazine and metazachlor was investigated in aqueous solution under UV-irradiation with and without H202. 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 H202 initial concentrations, the pesticide degradation was shown to be much more efficient than the degradation under UV-irradiation only. However, at high H202 concentrations ( > 2 mmol L-'), the efficiency of the UV/H202 system dropped down and the quantum yields of degradation were lower than for the direct photolysis. In the absence of H202, 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 H202 initial concentrations, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH l l . The results emphasize the potential of optimized reaction conditions in advanced oxidation.

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