Biochemical interactions between Glycine max L. silicon dioxide (SiO2) and plant growth-promoting bacteria (PGPR) for improving phytoremediation of soil contaminated with fenamiphos and its degradation products

Abstract

Fenamiphos is a systematic nematicide-insecticide used extensively for the control of soil nematodes. Fenamiphos and oxidation products have been known to induce water pollution, soil pollution and ecotoxicological effects on aquatic organisms, as well as heath issues. This contaminant can be removed by phytoremediation. Herein, we tested several strategies to improve the effectiveness of this technology. A combination of G. max plus Pseudomonas fluorescens was more efficient than G. max plus Serratia marcescens or G. max alone in degrading fenamiphos to other metabolites. Three major metabolites, namely fenamiphos sulfoxide (FSO), fenamiphos sulfone (FSO₂) and fenamiphos phenol (F-phenol), were detected in roots and leaves in which G. max amended with P. fluorescens or amended with S. marcescens produced a significant accumulation of FSO and FSO₂ with higher amounts than for G. max alone. Leaf concentrations of FSO were always higher than in the roots, while FSO₂ accumulated significantly more in G. max roots than in G. max leaves. In soil treated with fenamiphos, G. max roots and leaves alone, and in combined effects of plant and microorganisms, resulted in the disappearance of fenamiphos and the appearance of F-SO, F-SO₂ and F-phenol, which in turn caused toxic stress in G. max and the resulting production of reactive oxygen species such as H₂O₂ with higher content and an increase in antioxidant GPX activity. Although a batch equilibrium technique showed that use of SiO₂ resulted in the efficient removal of fenamiphos when compared with other treatments for removing adsorbed fenamiphos from soil, a fewer amount of fenamiphos was removed by G. max L. with SiO₂. H₂O₂ content and GPX activity increased in G. max under fenamiphos treatment and its degradation products, while amended G. max with SiO₂ or Argal led to a decrease in GPX activity and H₂O₂ content.

Keywords: Fenamiphos; H(2)O(2) content; P. fluorescens; POD activity; Phytoremediation; S. marcescens; SiO(2).