The degradation of fatty acid methyl esters improved the health of soils simultaneously polluted with metals and biodiesel blends

Abstract

Fuels from renewable biological resources are currently being used as an alternative or complement to petroleum-derived fossil fuels. The objective of this work was to investigate the degradation dynamics of commercially-available biodiesel blends (containing 1, 5 or 16% biodiesel, i.e. B1, B5 and B16) in soil simultaneously polluted with metals and biodiesel blends. To this purpose, soil was artificially polluted with 6,000 mg biodiesel blend per kg DW soil (B1, B5 or B16) and a mixture of metals: 1,500 mg Zn kg−1 DW soil + 500 mg Cu kg−1 DW soil + 50 mg Cd kg−1 DW soil. Artificially-polluted soils were then arranged in a phytotron under controlled conditions and monitored for 30 days. The bioremediation capacity of a bio-stabilized municipal solid waste, as organic amendment for biostimulation purposes, was evaluated. Soil health was monitored by measuring soil microbial indicators (biomass, activity and diversity parameters) and performing phytotoxicity bioassays with Cucumis sativus. The degradation of the fatty acid methyl esters (FAME) present in biodiesel was higher than that of the corresponding alkane homologues from diesel. The addition of the bio-stabilized municipal solid waste increased FAME degradation and microbial activity, and alleviated phytotoxicity. Cucumis sativus was more sensitive to pollution-induced effects than soil microbial communities. Our data showed that, after 30 days, organically-amended soils polluted with B16 experienced the greatest improvement in soil health (in the presence of the abovementioned metal mixture). It was concluded that biodiesel-containing fuel might cause a lower impact on soil health than diesel of fossil origin.