The Photodecomposition of Pesticides in Water

Sunlight decomposes many pesticides in water. Water provides a transparent and sometimes reactive medium in which air oxidations, for example, are effectively energized by ultraviolet light. In the presence of hydroxide ions or other nucleophiles, photonucleophilic displacement reactions result in hydrolysis and the conversion of aromatic halides to phenols and eventually to insoluble polymers. Photoreduction also may often be interpreted as a hydride ion transfer. Extensive degradation to small fragments and the combination of reactive intermediates with natural substrates may help explain the difficulties encountered in extending laboratory observations to field situations.