Biodegradation and Phytotoxicity of Biodiesel, Diesel, and Petroleum in Soil

The study aimed to investigate the biodegradation of contaminated soil with biodiesel, diesel, and petroleum by autochthonous soil microorganisms and also enriched with Bacillus subtilis by means of colorimetric method. The phytotoxicity was evaluated in recently contaminated soil and after 240 days to ensure the decrease of toxicity. The biodegradation assessment was carried out with redox 2,6-dichlorophenol indophenol (DCPIP) indicator and by the extraction of the contaminant in the soil with hexane. The amount of contaminant extracted from recently contaminated soil was compared to the amount found on the buried samples for 240 days. The phytotoxicity rates were evaluated by the use of Lactuca sativa seeds. Values of root and hypocotyl elongation were subjected to analysis of variance using the Kruskal-Wallis test. The results revealed that the autochthonous microorganisms were active on recently contaminated soil with biodiesel, because all biodiesel was biodegraded. Hence, only 0.001 g of biodiesel was extracted, and the phytotoxicity decreased after 240 days. On the other hand, the contaminated soil with diesel and petroleum was little active in 2,6-DCPIP test, and consequently, there was a large contaminant amount in soil after 240 days. Furthermore, petroleum and diesel were phytotoxic after biodegradation. The complex composition of the petroleum and diesel requires interactions of the microbial community able to biodegrade hydrocarbons and also metabolites from biodegradation. The naturally present microorganisms in the soil were capable of degrading the pollutant as much as the samples enriched with B. subtilis. The 2,6-DCPIP test is a simple and inexpensive methodology to analyze the potential biodegradation of all microorganisms of the soil and if the inoculation of the biodegrading microorganisms it will be necessary. Therefore, it would be helpful in bioremediation strategies.