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COVALENT BINDING OF REDUCED METABOLITES OF [15N3] TNT TO SOIL ORGANIC MATTER DURING A BIOREMEDIATION PROCESS ANALYZED BY 15N NMR SPECTROSCOPY. (R826646)
Citation:
Achtnich, C., E. Fernandes, J. Bollag, H. Knackmuss, AND H. Lenke. COVALENT BINDING OF REDUCED METABOLITES OF [15N3] TNT TO SOIL ORGANIC MATTER DURING A BIOREMEDIATION PROCESS ANALYZED BY 15N NMR SPECTROSCOPY. (R826646). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 33:4448-4456, (1999).
Description:
Evidence is presented for the covalent binding of
biologically reduced metabolites of 2,4,6-15N3-trinitrotoluene
(TNT) to different soil fractions (humic acids, fulvic
acids, and humin) using liquid 15N NMR spectroscopy. A
silylation procedure was used to release soil organic matter
from humin and whole soil for spectroscopic measurements.
TNT-contaminated soil was spiked with 2,4,6-15N3-trinitrotoluene and 14C-ring labeled TNT, before treatment
in a soil slurry reactor. During the anaerobic/aerobic
incubation the amount of radioactivity detected in the fulvic
and humic acid fractions did not change significantly (11-16%), whereas the radioactivity bound to humin increased
to 71%. The 15N NMR spectra of the fulvic acid samples were
dominated by a large peak that corresponded to aliphatic
amines or ammonia. In the early stages of incubation,
15N NMR analysis of the humic acids indicated bound azoxy
compounds. The signals arising from nitro and azoxy
groups disappeared with further anaerobic treatment. At
the end of incubation, the NMR shifts showed that nitrogen
was covalently bound to humic acid as substituted
amines and amides. The NMR spectra of the silylated
humin suggest formation of azoxy compounds and imine
linkages. Bound metabolites possessing nitro groups were
also detected. Primary amines formed during the anaerobic
incubation disappeared during the aerobic treatment.
Simultaneously, the amount of amides and tertiary amines
increased. Nitro and azoxy groups of bound molecules
were still present in humin at the end of the incubation
period. Formation of azoxy compounds from partially reduced
TNT followed by binding and further reduction appears
to be an important mechanism for the immobilization of
metabolites of TNT to soil.