Degradation kinetics of glucosinolates in soil.

Glucosinolates are compounds produced by all cruciferous plants. They can be hydrolyzed to several biologically active compounds and, as such, may serve as naturally produced pesticides. To optimize the pesticidal (biofumigation) effect and to assess the risk of glucosinolate leaching and spread in the environment, the degradation in soil of glucosinolates has been studied. The kinetics of degradation of four glucosinolates, two aliphatic (but-3-enyl and 2-hydroxy-but-3-enyl) and two aromatic (benzyl and phenethyl), in four soils was largely independent of the specific glucosinolate structure. Degradation followed logistic kinetics. Degradation was much faster in a clayey soil (half-life, 3.5-6.8 h) than in a sandy soil (half-life, 9.2-15.5 h). Degradation was much slower or nonexistent in the subsoil (<25 cm soil depth). The glucosinolates are not sorbed in the soil, and the degradation potential is, to a large extent, associated with the clay fraction. Measured activity in the soils of the enzyme myrosinase, which can catalyze the hydrolysis of glucosinolates, correlated well with the glucosinolate degradation kinetics. Autoclaving, but not sodium azide or gamma-irradiation, effectively blocked glucosinolate degradation, indicating that extracellular myrosinase is important for glucosinolate degradation.