Tracing the transformation of labelled [1-C-13]phenanthrene in a soil bioreactor

[1-C-13]-labelled phenanthrene was incubated in a closed bioreactor to stud y the flux and biotransformation of polycyclic aromatic hydrocarbon (PAH) i n contaminated soils on a bulk and molecular level. The degradation of extr actable phenanthrene was observed by GC-MS measurements and the mineralisat ion was monitored by (CO2)-C-13 production. The transformation of the C-13- label into nonextractable soil-bound residues was determined by carbon isot opic measurements. With these data we were able to calculate a carbon budge t of the C-13-label. Moreover, the chemical structure of non-extractable bo und residues was characterised by applying selective chemical degradation r eactions to cleave xenobiotic subunits from the macromolecular organic soil matrix. The obtained low molecular weight products yielded C-13-labelled c ompounds which were identified using IRM (isotope ratio monitoring)-GC-MS a nd structurally characterised with GC-MS. Most of the C-13-labelled product s obtained by chemical degradation of non-extractable bound residues are we ll-known metabolites of phenanthrene. Thus, metabolites of [1-C-13]phenanth rene formed during biodegradation appear to be reactive components which ar e subsequently involved in the bound residue formation. Hydrolysable amino acids of the soil residues were significantly labelled with C-13 as confirm ed by IRM-GC-MS measurements. Therefore, phenanthrene-derived carbon was tr ansformed by anabolic microbial processes into typical biologically derived compounds. These substances are likely to be incorporated into humic-like material after cell death. (C) 2000 Elsevier Science Ltd. All rights reserv ed.