Photolytic degradation of 2,4-D onZea maysleaves

Growth chamber experiments were conducted to determine the effects of UV light and riboflavin on photolysis of 2,4-D applied toZea maysleaves. Droplets of 100 mg L−114C-2,4-D were applied toZ. maysleaves with and without 10 mg L−13H-riboflavin and exposed to either UV-enhanced or UV-attenuated polychromatic light in a time-course assay. Photolysis of nonabsorbed14C-2,4-D residues onZ. maysleaves was sensitized by riboflavin regardless of UV light regime, but a larger percentage of nonabsorbed herbicide was degraded under UV-enhanced light compared to UV-attenuated light. Riboflavin was almost completely photolyzed during the first 10 h of exposure; yet, photolysis of14C-2,4-D surface residues in treatments containing riboflavin increased from 59% at 10 h of exposure to 87% at 42 h of exposure. In corresponding treatments without riboflavin, photolysis of14C-2,4-D surface residues was 37% at 10 h of exposure and 84% at 42 h of exposure. In contrast, only 7% of the14C-2,4-D deposited on glass microscope slides was degraded after 42 h of exposure in the absence of riboflavin, whereas 59% was degraded in the presence of riboflavin. Photolysis of 2,4-D onZ. maysleaves in treatments without riboflavin suggests that certain epicuticular component(s) ofZ. maysacted as photosensitizers or catalytic agents that promoted photolysis of nonabsorbed 2,4-D residues.