Metolachlor photodegradation study in aqueous media under natural and simulated solar irradiation

To elucidate the photochemical behavior of pesticide metolachlor, degradation was carried out in aqueous media of different compositions such as sea, river, lake, and distilled water under natural and simulated solar irradiation. In addition, the effect of important constituents of natural water such as dissolved organic matter (DOM, isolated from Pamvotis Lake) and nitrate ions was also examined. It was found that photodegradation proceeds via a pseudo-first-order reaction in all cases. The presence of DOM inhibits the photolysis reaction with half-lives ranging from 87 to 693 h whereas the degradation rate was accelerated up to 11 times in the presence of NO(3)(-). In addition, the toxicity of the degradation products formed (generally through hydroxylation, dealkylation, and cyclization reactions) was also performed using the marine luminescent bacterium Vibrio fisheri. Our results indicated a toxicity increase of the irradiated solution showing that photoproducts of higher acute toxic effects were formed.