Humification of PAH and TNT During Bioremediation — Evaluation of Long Term Risk and Sustainability

Abstract

The depletion of contaminants in soil is not only based on degradation or min- eralisation, but also on the fact that a fixation or immobilisation of the xenobiotic substances as bound residues takes place within the soil matrix. This binding of organic contaminants (called a humification process if bound to soil humus) can reduce the bioavailable and analytically detectable part of the xenobiotics. The binding was investigated in detail by the use of 14C-labeled substances for PAH and TNT in the last decades and this immobilisation process has been proposed as a remediation measure. The intentional humification process may be achieved by adjusting bioremediation process parameters such as the supplementation of soil with organic substances (compost etc.) or by changing the incubation conditions (anaerobic and aerobic phases). The application of this humification strategy however, requires a careful study of the factors which influence the formation and long term fate and stability of these bound residues. The fixation/immobilisation could be accepted as a reme- diation technique if in the long run, no hazardous substances (original substances or metabolites) can be remobilised in an available form (extractable or even water soluble). This demands a stable covalent binding of the contaminants (and/or their metabolites) to the soil matrix. This paper will give a brief overview of recent investigations on this topic. For completeness also Chapters 15, 16, 17, 18, 20 and 27 should be respected.