Bioavailability and toxicity of imazethapyr in maize plant estimated by four chemical extraction techniques in different soils

Abstract

The bioavailability and toxicity of herbicides on the crop depend on its uptake efficiency from the soil, and thus the assessment of the bioavailable fraction of herbicides in soil is a crucial work. In this study, we investigated the uptake concentration and toxicity of imazethapyr in maize plant using four chemical measurements, including the extraction of in situ pore water (CIPW), ex situ pore water (CEPW), organic solvent (Csoil) and passive sampling (Cfree) in five soils. The results obtained that the CIPW in a specific soil had the most significant correlation with the uptake concentration of imazethapyr in maize plant (R2 = 0.8851–0.9708), followed by CEPW (R2 = 0.8911–0.9565) and Cfree (R2 = 0.7881–0.9673). However, Cfree showed a higher correlation when considering all five soils, and thus Cfree can describe the bioavailability beyond the types of soil. Additionally, the median inhibition concentrations (IC50) of imazethapyr to maize plant ranged from 5.0 to 6.9 mg/kg in five soils, and the CIPW, CEPW and Cfree had better relationships with the IC50 (R2 > 0.8681) than the Csoil (R2 = 0.6782). The effects of soil properties on the phytotoxicity of imazethapyr, including pH, organic matter content, cation exchange capacity and clay content, were studied, and the soil pH was shown to be a main factor. This study demonstrated that the freely dissolved fraction and soil pore water concentration of imazethapyr in soil can be used to evaluate its bioavailability and toxicity to maize.