Persistence and metabolism of imazapyr in four typical soils of Zhejiang Province (China)

Abstract

A laboratory experiment was conducted to study the effects of two different formulations (25% Arsenal SL and 5.0% Arsenal G) and doses (equivalent to 0.5 ug A.I. g−1 and 1.0 ug A.I. g−1 soil) on persistence of imazapyr in four soils of Zhejiang province, southeastern China. Based on the first-order kinetic equation, the calculated half-lives of imazapyr were in the range 22.0–35.7 days among all the treatments. With regard to the four soils, the highest (30.9 days) and lowest (24.1 days) mean half-lives were observed in Soil C (Coastal Saline Soil, pH 8.78) and Soil B (Yellow-Red Soil, pH 5.25), respectively. The persistence of imazapyr increased in the order soil C (pH 8.78) > soil A (Silt-Loamy Paddy Soil, pH 7.86) > soil D (Fluvio-Marine Yellow Loamy Soil, pH 7.06) > soil B (pH 5.25), which demonstrated that an increase in soil pH tended to lead to higher persistence of imazapyr in soil. The difference between the mean half-lives, corresponding to 0.5 and 1.0 ug A.I. g−1 soil treatment for 25% Arsenal SL or for 5.0% Arsenal G, respectively, was not significant, which showed that the different initial application rates had little impact upon degradation of imazapyr. In contrast, a greater impact of the different formulation type upon persistence of imazapyr was observed. Higher persistence was observed with the granular formulation (t 1/2 = 28.1 d) compared with the liquid formulation (t 1/2 = 26.2 d) for the lower dose, which was statistically significant, and an identical trend also existed in the higher dose. Three major metabolites were separated by preparative TLC. On the basis of their spectral data (IR, LC-MS and 1H NMR), the structure of each compound was deduced and their formation pathway was also discussed.