Biodegradation of Soybean Biodiesel Generates Toxic Metabolites in Soil
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Biodegradation of Soybean Biodiesel Generates Toxic Metabolites in Soil Jaqueline Matos Cruz & Renato Nallin Montagnolli & Ederio Dino Bidoia
Received: 22 April 2020 / Accepted: 29 July 2020 # Springer Nature Switzerland AG 2020
Abstract Biodiesel is a mixture of fatty acid methyl esters (FAME) from either vegetable oils or animal fats. Although biodiesel biodegrades faster than diesel fuel, the impacts of this biofuel in environment throughout its biodegradation process should be investigated. For this reason, the objective of the present study was to evaluate the microbial activity, the phytotoxicity, and the formation of metabolites during biodegradation of the contaminated soil with biodiesel. Microbial activity was evaluated using culture-dependent methods in soil samples artificially contaminated with biodiesel—followed by pH adjustments. The formation of metabolites during biodegradation was identified using gas chromatography coupled with mass spectrometry (GC/MS). Highlights • The biodiesel biodegradation generates methanol as metabolites. • The metabolites from biodiesel biodegradation cause complete inhibition of seed germination and cultivable microorganisms. • The buffering of the soil with soda lime granules reduced the methanol produced during biodegradation. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11270-020-04801-w) contains supplementary material, which is available to authorized users. J. M. Cruz : E. D. Bidoia (*) Department of Biochemistry and Microbiology, São Paulo State University (UNESP), Avenue 24-A, 1515, Rio Claro 13506-900, Brazil e-mail: [email protected] R. N. Montagnolli Federal University of São Carlos (UFSCar), Rod. Anhanguera km 174 - SP-330, Araras 13600-970, Brazil
Respirometric method was also applied to evaluate total microbial activity. Seeds of Cucumis sativus were sown in soil samples before and after biodegradation to expand our knowledge on the impacts of such metabolites in a eukaryotic test-organism. Culture-dependent assays successfully allowed the quantification of microorganisms during biodegradation. According to CO2 production, biodiesel initially acted as a biostimulation agent increasing microbial activity. Indigenous microbiota degraded biodiesel into smaller compounds such as pentane, free fatty acids, and methanol. Soil pH significantly dropped from 5.4 to 3.0 after 120 days of biodegradation as a result of high concentration of free fatty acids. These free fatty acids inhibited further microbial growth after biodegradation. It was proposed that correcting soil acidity during biodegradation would be enough to sustain microbial growth. However, pH decrease was just one of the factors that inhibited microbial growth and plant root development. It was proposed that biodegradation yielded toxic metabolites such as methanol. These metabolites contributed to impair the root elongation due to alcohol-specific properties to solubilize a wide variety of lipids within the seed. Therefore, the present study draws
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