The influence of a NAPL on the loss and biodegradation of C-14-phenanthrene residues in two dissimilar soils

摘要

This study was carried out to assess the influence of diesel, applied over a log concentration range, on the loss and extractability of phenanthrene (measured as putative C-14-phenanthrene residues) in two different soils. The influence of diesel on the ability of a cyclodextrin based extraction method to predict the microbial bioavailability of C-14-residues was also assessed. An increase in loss Of C-14-residues with increasing diesel concentration from 0 to 2000 mg kg(-1) was generally observed with time in both soils. It is suggested that this trend is attributable to competitive sorption for soil sorption sites and to a lesser extent to displacement of C-14-residues from soil sorption sites by diesel resulting in greater compound availability and therefore greater loss by degradation via the actions of indigenous microorganisms. However, in the 20 000 mg kg(-1) diesel treatments of both soils, results indicated a delayed loss. It is suggested that this retarded loss was due to the formation of a discrete NAPL-phase into which C-14-phenanthrene residues partitioned, thereby decreasing their availability and as a consequence their degradation. Furthermore, it is suggested that nutrient limitation may have slowed down degradation rates as diesel concentrations increased. Comparison between cyclodextrim-extractability and microbial mineralisation supported the use of cyclodextrin to assess microbial bioavailability of C-14-residues after 50 d or more ageing up to diesel concentrations of 2000 mg kg(-1). However, results suggested that at high diesel concentrations (specifically 20 000 mg kg(-1)) co-extraction of C-14-phenanthrene residues may have occurred as a result of the combined solvating powers of both the cyclodextrin and the diesel. Furthermore, mineralisation of C-14-phenanthrene residues may have been affected by extreme nutrient limitation in this treatment. (c) 2006 Elsevier Ltd. All rights reserved.