, 2000) and is expected to limit the extent of 14C-phenanthrene biodegradation in the soils; low TOC in soils can be an indication

of low microbiological activity (Margesin & Schinner, 2001). Samples taken in the selected sites were mostly bare of vegetation and plate counts revealed very low CFUs (Fig. 3) for both total heterotrophs and 14C phenanthrene-degrading bacteria. The presence of only small LDK378 chemical structure numbers of PAH-degrading bacteria can be explained by the absence of degradation inducing chemicals from both biogenic and anthropogenic sources. Sufficient concentrations of biogenic volatile organic chemicals (VOCs) from plants (Wilcke, 2007; McLoughlin et al., 2009) and anthropogenic compounds have been identified as carbon sources for microbial activity, growth and the induction of appropriate genes for PAH degradation in indigenous microorganisms (Macleod & Semple, 2002; Johnsen & Karlson, 2005). Hydrocarbon degraders have been cultivated at levels > 105 cell g−1 from contaminated polar soils and have increased following oil spillage by 1–2 orders of magnitude in hydrocarbon contaminated soil compared with pristine soils (Aislabie et al., 2000). In this study, CFUs of 14C-phenanthrene-degrading bacteria increased in all five soils and by one order of magnitude in soils 1, 3 and 5 after mineralization in slurry PARP inhibitor conditions (Fig. 3). Of the three temperatures

used in this study, 4 °C was the most representative of prevailing temperatures at Livingstone Island hence appropriate for optimum microbial activity. However, no significant amount of 14C-phenanthrene was mineralized in any of the five soils (Table 2). Reduced bioavailability of PAHs at low temperatures has also been reported as a possible reason for

low levels of microbial degradation (Eriksson et al., 2003). At low temperatures, the solubility and bioavailability of less soluble hydrophobic organic compounds, such as PAHs, decrease because of an increase in viscosity in the physical nature of the compounds and because of stronger sorption to the soil organic matter. Increased viscosity will decrease the degree of organic compound distribution (less surface area for microbial action) and subsequent diffusion rates to sites of biological action Cyclic nucleotide phosphodiesterase leading to reduced extents of degradation (Nam & Kim, 2002). Ferguson et al. (2003a, b)obtained similar results when they found that mineralization of 14C-labelled octadecane was virtually absent at temperatures below or near the freezing point of water. At 12 °C, the extents of 14C-phenanthrene mineralized increased significantly in two of the five soils after a long lag phase. 14C-Phenanthrene was mineralized to a greater extent at 22 °C than at 4 and 12 °C for all the soils. The increasing solubility of phenanthrene with increasing temperature would mean that the amount of phenanthrene in solution (and therefore available for degradation) would have been higher at 22 °C that at 4 and 12 °C.