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Bioavailability of an organophosphorus pesticide, fenamiphos, sorbed on an organo clay

journal contribution
posted on 2003-04-23, 00:00 authored by N Singh, M Megharaj, Will GatesWill Gates, G J Churchman, J Anderson, R S Kookana, R Naidu, Z Chen, P G Slade, N Sethunathan
Hydrolysis of an insecticide/nematicide, fenamiphos [ethyl-3-methyl-4-(methylthio)phenyl-(1-methylethyl)phosphoramidate], immobilized through sorption by cetyltrimethylammonium-exchanged montmorillonite (CTMA-clay) by a soil bacterium, Brevibacterium sp., was examined. X-ray diffraction analysis, infrared spectra, and a negative electrophoretic mobility strongly indicated that fenamiphos was intercalated within the bacterially inaccessible interlayer spaces of CTMA-clay. The bacterium hydrolyzed, within 24 h, 82% of the fenamiphos sorbed by the CTMA-clay complex. There was a concomitant accumulation of hydrolysis product, fenamiphos phenol, in nearly stoichiometric amounts. During the same period, in abiotic (uninoculated) controls, 4.6% of the sorbed insecticide was released into the aqueous phase as compared to 6.0% of the sorbed fenamiphos in another abiotic control where activated carbon, a sink for desorbed fenamiphos, was present. Thus, within 24 h, the bacterium hydrolyzed 77% more fenamiphos sorbed by organo clay than the amounts desorbed in abiotic controls. Such rapid degradation of an intercalated pesticide by a bacterium has not been reported before. Evidence indicated that extracellular enzymes produced by the bacterium rapidly hydrolyzed the nondesorbable fenamiphos, even when the enzyme itself was sorbed. Fenamiphos strongly sorbed to an organo clay appears to be readily available for exceptionally rapid degradation by the bacterium.

History

Journal

Journal of agricultural and food chemistry

Volume

51

Issue

9

Pagination

2653 - 2658

Publisher

American Chemical Society

Location

Washington, D.C.

ISSN

0021-8561

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2003, American Chemical Society