Hydrolysis, aqueous photolysis and soil degradation of fluroxypyr

Abstract

The fate of fluroxypyr in the aqueous buffer solutions, natural water and three types of soil was examined under laboratory conditions. The hydrolysis of fluroxypyr was studied in aqueous buffer solutions of pH 4.5 ± 0.1, 7.4 ± 0.1 and 9.0 ± 0.1 at different temperatures (25 ± 2 and 50 ± 2 °C). Fluroxypyr was stable under pH 4.5 ± 0.1 acid condition and its half-lives in pH 7.4 ± 0.1 and 9.0 ± 0.1 buffer solutions at 25 ± 2 °C were 14.9 and 12.7 days, respectively. The chemical hydrolysis of fluroxypyr was both pH and temperature-dependent and accelerated by alkaline conditions and higher temperatures. The photodecomposition rate of fluroxypyr under UV light in aqueous buffer solutions and natural water was much higher than that under sunlight with the half-lives of 0.102–0.705 hour. The half-lives of direct photolysis in pH 7.4 ± 0.1 and 9.0 ± 0.1 buffer solutions were 7.14 and 5.34 days respectively and no significant variations of concentrations could be observed in natural water, distilled water and pH 4.5 ± 0.1 buffer solution samples. Photosensitisers such as H₂O₂ or riboflavin could strongly enhance photolysis of fluroxypyr in natural sunlight with half-lives ranging from 0.36 to 43.6 hours in water and buffer solutions. 4-amino-3, 5-dichloro-6-fluorop-yridin-2-ol and 4-amino-3, 5-dichloro-6-hydroxy-2-pyridyloxyacetic acid were identified as degradation products by LC-TOF-MS. The degradation of fluroxypyr in three nonsterilised Chinese soil samples followed first-order kinetics, with half-lives ranging from 27.2 to 43.1 days. No degradation of fluroxypyr occurred in sterilised soil samples up to 70 days. The data generated from this study could be helpful for risk assessment studies of the pesticide in the environment.

Keywords:

• fluroxypyr
• hydrolysis
• hydrolyzate
• photolysis
• photoproduct
• soil degradation

Acknowledgement

This study was sponsored by the Institute for the Control of Agrochemicals, Ministry of Agriculture of the People’s Republic of China.