Effect of soil properties on adsorption, degradation and leaching potential of four herbicides

Once a herbicide is introduced into the environment, some risks are inevitable as it can trigger accumulation, leaching and runoff, thus contaminating soil and water resources. For a proper risk assessment, the present study investigates the adsorption, degradation and leaching behaviour of pretilachlor, butachlor, anilofos and pendimethalin. Among the studied herbicides, pendimethalin (KFads 1.466 ± 0.087 to 2.569 ± 0.072 µg1–1/n g−1 ml1/n; DT50 65.34–120.29 days) has the highest adsorption and persistence in soil, followed by anilofos (KFads 0.967 ± 0.063 to 1.637 ± 0.077 µg1–1/n g−1 ml1/n; DT50 37.12–77.63 days), butachlor (KFads 0.722 ± 0.077 to 1.273 ± 0.067 µg1–1/n g−1 ml1/n; DT50 31.23–65.13 days) and pretilachlor (KFads 0.834 ± 0.066 to 1.422 ± 0.071 µg1–1/n g−1 ml1/n; DT50 26.32–61.36 days). Pretilachlor, butachlor, anilofos and pendimethalin leached up to 40–60, 30–40, 20–30 and 10–20 cm soil layers, respectively, indicating that pendimethalin was least mobile in the studied soils. Increase in simulated rainfall (300 mm) increased the downward mobility of herbicides. Among different soils, herbicide degradation and leaching were highest in loamy sand and decreased with an increase in organic matter (OM) content, while adsorption was lowest in loamy sand and increased with an increase in OM content. The addition of farmyard manure amendment reduced the mobility of pretilachlor, butachlor, pendimethalin and anilofos, and these leached up to 20–30, 20–30, 0–10 and 10–20 cm soil layers, respectively. The results indicated that organic amendments can be used as an effective management practice for controlling groundwater contamination.