Flavonoid Stability and Biotransformation in Agricultural Soils: Effects of Hydroxylation, Methoxylation, and Glycosylation

Stricter pesticide regulations are increasing the demand for environmentally acceptable alternatives with flavonoids seen as promising candidates for use as biopesticides. However, the current limited understanding of the environmental fate of flavonoids in soils restricts their assessment as active pesticide ingredients. To address this knowledge gap, we conducted laboratory incubation experiments with LC-MS-based quantification to determine the half-lives of 18 structurally related flavonoids in three agricultural soils. Hydroxylated flavonoids were rapidly transformed (t_1/2: 3–12 h), while methoxylated derivatives exhibited substantially longer half-lives, which increased with the number of methoxy groups (t_1/2: 5–460 h). Glycosylated flavonoids were primarily transformed into their aglycones (t_1/2: 0.5–5 h). Incubation experiments with autoclaved soil indicated that biotic processes primarily catalyzed the observed transformations. All trends were consistent across different soil types and pH values. This study provides a comprehensive overview of flavonoid stability in agricultural soils, enhancing our understanding of their potential as alternative pesticides.