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The aim of the study was to determine changes in phytotoxicity levels during bioremediation of soil contaminated with 5% (v/w) diesel oil and find their correlation with the effectiveness of hydrocarbon degradation. Bioremediation trials were performed using a Gordonia alkanivorans S7 strain. The clean-up process was enhanced through the addition of dried fungal enzymatic preparations obtained from fungi Phanerohaete chrysosporium and Aspergillus niger. After 110 days of bioremediation the decrease in soil pollution ranged between 68 and 77% depending on treatment conditions. Toxicological tests using marker plants revealed significant differences in the phytotoxicity levels of soil during bioremediation, depending on the treatment variant. The addition of an enzymatic fungal preparation to soil was found to accelerate the rate of contaminant degradation. The rate of hydrocarbon depletion in subsequent phases of the remediation process was found to be correlated with the phytotoxicity level. The obtained results provide evidence that phytotests can be useful tools for monitoring toxicity changes during bioremediation either mediated only by bacteria or additionally stimulated by fungal enzymatic preparations.

Commercialization of biodiesel and its blends with diesel oil may lead to the appearance of spills during transport or the leakage of contaminated wastewater into soil. The impact of biodiesel, either pure or blended with diesel oil, on natural habitats has been poorly characterized. The goal of this study was to assess the potential of a bacterial strain, Gordonia alkanivorans S7, for remediation of soil contaminated with biodiesel, traditional fossil fuels or their blends (diesel oil, B20 diesel oil/biodiesel blends, P31 petroleum fraction). This was achieved by evaluating the changes in fuel concentration and the activity of extracellular microbial dehydrogenases in soil, as well as measuring the soil's pH under controlled conditions. The removal of biodiesel from contaminated soil, in the event of its 4% initial concentration, was almost complete (99%), but in cases of higher concentrations (5% or 8% w/w) the efficiency of Fatty Acid Methyl Ester (FAME) degradation was 90% and 60%, respectively, after 90 days biodegradation. In soil samples contaminated with biodiesel, the activity of dehydrogenase was very low in the initial stage of the process (only 10 μmol triphenylformazan (TPF) per g of dry weight (g dw !1