Microbial activity in two soils with different clay content contaminated by different diesel/biodiesel mixtures

Biodiesel is an alternative energy source that has a high biodegradability potential and low toxicity, contributing to ecosystem impact reductions. The aim of this study was to determine, by the natural attenuation technique, the microbial activity of two soils: one clayey (CLA) and the other sandy (SAN), contaminated with different concentrations of biodiesel blended with diesel (B0, B5, B20 and B100) simulating a surface spill. The respirometry, fluorescein diacetate (FDA) hydrolysis and cultivable heterotrophic bacteria and actinobacteria count techniques were used to determine the microbial activity in the different microcosms at up to 48 days of incubation. For the respiration activity, the CLA soil was most active at all mixed fuel concentrations (B0, B5, B20 and B100), as compared to the SAN. Furthermore, the biodiesel addition to the two soil types contributed to the microbial activity increase, and higher CO2 release values were found in the B20 and B100. For the FDA activity, it was found that the CLA soil showed higher activity at the B5 and B20 concentrations, and heterotrophic count showed a tendency towards a CFU g-1 decrease as the incubation time increased. This indicates that the CLA soil, due to a higher amount of nutrients, clay, organic matter and CEC, was associated with the addition of biodiesel and showed higher microbial activity. The results obtained in this study contribute to future studies of surface contamination by different mixtures of diesel/biodiesel in soils with similar physical and chemical characteristics