Enzyme-Mediated Transformation of 17 Beta-Estradiol in Soil.

Our present study revealed that 17β-estradiol (E2), a natural hormone, can be effectively transformed in soil through reactions mediated by laccase and horseradish peroxidase (HRP), the enzymes widely present in nature in extracellular forms. Experiments were conducted using a Cecil sandy clay loam soil preloaded with 0.2 µg E2 g^-1 soil and subjected to treatments of laccase and HRP. After 264 hours of incubation in saturated soil condition, system with 10 U laccase showed 94.6% reduction in extractable E2 while 85.6% reduction at 5 U and 87.1% reduction at 2.5 U were reported. In soil maintained at field water capacity the extractable E2 reduced by 91% after 264 hours with 10 U of laccase. In HRP treated saturated soil after 264 hours, only 8.4% E2 was extractable with 2 U HRP application while for system containing 10 U HRP, 2.5% E2 was extractable. However in soil systems containing 10 U HRP but maintained at field water capacity, extractable E2 after 264 hours was 10.1%. We also compared E2 removal, laccase, and HRP activity behavior in water to that in soil. To interpret possible transformation pathways, we examined E2 transformation in soil using ¹⁴C-labeling in combination with soil organic matter (SOM) extraction and size exclusion chromatography. We found inclusion of ¹⁴C labeled E2 in humic acid and size exclusion chromatograms of extracted humic acid showed distinct changes in chromatographic patterns of laccase catalyzed samples than control. This suggests changes in humic substances of soil organic matter brought due to oxidative reactions of laccase and HRP. The study provides useful information for understanding and assessing the environmental fate of hormones and for developing a novel soil remediation strategy via enzyme-enhanced humification reactions.