Imazosulfuron (IMZ) is a potent broad spectrum herbicide, approved for use on sod and rice in the US. Previous reports indicate it is photolabile, but focus on product identification rather than kinetics. The photolytic rate and the relative contribution of direct and indirect processes were determined. Dissolved organic matter (DOM) photosensitization was investigated using reference fulvic acids and whole collected rice field water. Scavenger and anoxic experiments indicated that the main indirect pathway for IMZ oxidation was by triplet excited-state DOM (3DOM), and not by reactive oxygen species such as hydroxyl radical and singlet oxygen. However, photolytic rates were fastest in water without DOM, indicating that the relative contribution of 3DOM to environmental photolysis is small and direct photolysis predominates. Environmentally-relevant variances in temperature, turbidity and salinity did not significantly influence degradation rates. The experimentally derived quantum yield for direct photolysis (2.94x103) was used to predict the half-life of IMZ in California (3.6 d) and was compared to radiation under natural light.

Role of dissolved organic matter on imazosulfuron photolysis

251st National Meeting (2016)

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