Transformation of monuron photosensitized by soil extracted humic substances: energy or hydrogen transfer mechanism?

The humic and fulvic acids extracted from a Ranker type soil sensitize the transformation of monuron. When monuron is irradiated at 365 nm in the presence of the fulvic acid, its degradation is faster in deoxygenated medium than in air-saturated solution. Chloride ions are released, and the para-hydroxylated derivative is formed as upon direct photolysis. It is deduced that the consumption of monuron observed in the absence of oxygen is due to an energy transfer from reactive triplet states of the fulvic acid to monuron. Energy transfer reactions also take place when hydroquinone or acetophenone are used as sensitizers, showing that the energy level of the triplet state of monuron is lower …