Photosensitized degradation of terbuthylazine in water

We investigated the photodegradation of terbuthylazine, an s-triazine herbicide, in the presence of hydrogen peroxide (H2O2), titanium dioxide (TiO2), acetone or humic substances. In the presence of H2O2 and UV light, the degradation of terbuthylazine quickly leads to the formation of ammeline. The degradation pathway consists of dealkylation reactions giving 2-chloro-4,6-diamino-1,3,5-triazine, and then ammeline through hydroxylation. Irradiation of terbuthylazine with simulated solar light in the presence of titanium dioxide gives also dealkylation products in the first stage of degradation. Acetone at *1 % (v/v) produces a 7-fold enhancement of the degradation rate. In the presence of humic substances, different results were obtained, depending on the origin of the substances tested. The humic acids isolated from a soil accelerate the degradation speed, whereas the fulvic acids from a small stream reduce it.