Sorption, persistence and leaching of abscisic acid in agricultural soils: An enantiomer-selective study

Abstract

Little is known about the enantioselectivity of the processes that determine the efficacy and environmental fate of natural compounds with potential to be used as environmentally-friendly agrochemicals. We conducted incubation and column leaching experiments to examine the extent and enantioselectivity of the sorption, persistence, and leaching of (RS)-abscisic acid (ABA) in three agricultural soils. Sorption of ABA enantiomers was a non-enantioselective process that occurred only in the soil with pH close to the pKa (4.8) of ABA enantiomers, but not in the two other (alkaline) soils. The degradation of (RS)-ABA was enantioselective for the three soils tested. (S)-ABA, the naturally-occurring enantiomer, was always degraded faster (DT50 < 4 days), compared to (R)-ABA (DT50 > 8 days). The movement of ABA enantiomers through the soil profile was enantioselective with column leachates being enriched in (R)-ABA enantiomer. Leaching was delayed in the soil that displayed sorption for both enantiomers. The results showed that the behavior of ABA enantiomers in soil was enantioselective and that the final fate of (R)-ABA and (S)-ABA depended on the soil type and appeared to be affected by their sorption on soil. The longer persistence of (R)-ABA should be considered when assessing the possibility of using this enantiomer or formulations containing enantiomer mixtures of ABA for crop management.