Degradation of imazapyr and imazapic in aqueous solutions and soil under direct sunlight.

Photolytic degradation of imazapyr and imazapic in aqueous solutions (pH 3, 7 and 9) and soil under direct sunlight were studied. A total of 0.1 mL of aqueous solutions containing herbicides were collected at 0, 1, 2 and 3 days and were directly analyzed using high performance liquid chromatography equipped with ultraviolet detector (HPLC-UV) without further clean-up process. Soils that were treated with herbicides were sampled at seven different days (0, 1, 5, 10, 16, 23 and 30). The photolytic results showed that imazapyr and imazapic degraded faster in solutions compared to soils (> 90%). Photolysis of imidazolinone herbicides became more effective as the pH value increased. The half-lives for imazapyr and imazapic degradation on soil surface under sunlight were calculated at 126 days and 85.56 days, respectively. Low degradation of imazapyr and imazapic in soil becomes a concern since it may contribute to the persistency of imidazolinone herbicides in this media. The use of these herbicides should be planned well to reduce the risk of herbicides leaching into groundwater and posing risk to non-target crops