Mineralisation of 14C-phenanthrene in PAH-diesel contaminated soil: Impact of Sorghum bicolor and Medicago sativa mono- or mixed culture

Abstract

Plant-assisted biodegradation can offer a cost-effective and sustainable approach for the bioremediation of PAHs in soil. As such, selecting the most appropriate plant species is important. The potential for plant-assisted biodegradation of complex PAH-diesel mixtures in soil by sorghum (Sorghum bicolor) and alfalfa (Medicago sativa) grown as monocultures and mixed cultures using 14C-contaminants has not been widely reported. The objective of this study was to assess 14C-phenanthrene mineralisation profiles in mixtures of PAH-diesel in soil in the presence of Sorghum bicolor and Medicago sativa. Soil was spiked with PAHs and diesel, after which M. sativa and S. bicolor were introduced and grown as mono- or mixed- cultures. The toxicity of the PAH-diesel oil mixture in the planted treatments, as well as its effect on the mineralisation of 14C-phenanthrene were evaluated. Monocultures of both plant species tolerated the complex PAH-diesel mixtures based on growth and survival, and increased rates and extents of 14C-phenanthrene mineralisation in soil. The influence of PAH concentration on 14C-phenanthrene mineralisation profiles varied in planted and unplanted treatments. The rates and extents of 14C-phenanthrene mineralisation tended to decrease in diesel amended soil, especially at low PAH concentrations. To the best of the authors’ knowledge, this is the first report of 14C-phenanthrene mineralisation patterns in complex PAH-diesel oil mixtures contaminated soil especially with respect to the specified plant species. The findings offer new insights on mono- and multi-species phytotoxicity as well as plant-assisted biodegradation of PAH mixtures in soil which may be useful in the risk assessment and remediation of contaminated sites.