Biomass and activity of microorganisms in a fuel oil contaminated soil

The measurement of microbial biomass in soils contaminated by fuel oil was investigated using the CHCl3 fumigation-extraction method. It was shown that usually no significant amounts of fuel oil were additionally made extractable by CHCl3 fumigation. Thus, the fumigation-extraction method can be used in fuel oil contaminated soils. In the two fuel oil treatments of an incubation experiment 87% (0.5% oil-C) and 82% (1.0% oil-C) of the added C were mineralized to CO2 in 165 days. Only 5.2% (0.5%-oil-C treatment) and 8.5% (1.0%-oil-C treatment) of the added fuel oil could be measured at the end of the experiment. The soil microbial biomass content (biomass C, biomass N and biomass ninhydrin-reactive N) of the control soil and that of the 0.5%-oil-C treatment showed some fluctuations, but no marked changes during the incubation. The microbial biomass content in the 1.0%-oil-C treatment had increased significantly by the end of the incubation. The amount of inorganic N incorporated into organic matter at the end of the incubation showed that the portion of fuel oil, not recovered as CO2 or extracted as fuel oil residue, could be explained by the formation of microbial biomass and microbial residual mass. Significant amounts of chemically-unchanged “bound residues” are extremely unlikely at this time.