Abstract
After the application of herbicides, their migration and transformation in the environment are closely related to their adsorption characteristics in the soil. The adsorption of herbicides in soil is also important when evaluating their environmental behaviors or risks. Pyraclonil is a contact herbicide widely used to control weeds in paddy fields, especially in Japan. This study investigated the adsorption and desorption behaviors of pyraclonil in eight typical agricultural soils across China. Surface soil samples (0–15 cm) were collected in farmland across China, including Hebei luvisols, Heilongjiang phaeozems, Sichuan gleysols, Zhejiang anthrosols, Jiangxi ferralsols, Shandong alisols, Hubei lixisols, and Hainan plinthosols. Adsorption-desorption experiments were conducted at 25 °C ± 1 °C using a batch equilibration method. Pyraclonil residue was analyzed using high-performance liquid chromatography-mass spectrometry. The adsorption and desorption isotherms of pyraclonil in the eight soils are fitted well by mathematical models. The isothermal adsorption-desorption curves of pyraclonil agree with the simulation results of the Freundlich model. The adsorption of pyraclonil is mainly physical, and all adsorption isotherms are of type L. The adsorption constants range from 3.2 to 28.6 mg1−1/n L1/n kg−1. The desorption curves of pyraclonil in all soils show positive hysteresis, as the hysteresis coefficients are in the range of 0.01–0.26. The adsorption and desorption constants increase with increasing soil organic matter content and cation exchange capacity, but they are not related to soil pH and clay content. Pyraclonil exhibits low adsorption in different agricultural soils, and the adsorption process is irreversible. Pyraclonil has moderate or high mobility in different agricultural soils (except phaeozems with high organic matter content) across China, and pyraclonil could be transported from soil to groundwater after its application. Therefore, pyraclonil poses some risks to surface water and groundwater.
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