Remediation of an oil-contaminated soil by two native plants treated with biochar and mycorrhizae.

Soil contamination by petroleum compounds threatens the health of soil and water resources. This research was conducted with the objective of reaching an efficient technique for the removal or reduction of harmful effects caused by total petroleum hydrocarbons (TPH) in soils. In a greenhouse experiment, the effect of biochar (B), mycorrhizae (M) and combination of mycorrhizae and biochar (M + B) on the growth of two native species; clover (Trifolium arvense) and mallow (Malva sylvestris L.), and removal efficiency of TPH (16.79 mg kg-1) from an oil-contaminated soil were studied. The plant analyses after 50 days of growth period showed a significant (p ≤ 0.05) increase in shoot dry weight of mallow in B and M + B treatments but no significant effect was observed for clover compared to the control (C). The initial TPH concentration, determined by gas chromatography technique was reduced from 9.4% in unplanted soil until 56.4% (clover) and 55.9% (mallow) in M + B treatment. The relative concentration of long chain alkanes (LCAs) were also reduced when treatments were applied, in which the highest and lowest reductions was found in C21-C25 and C11-C15, respectively, though octacosane (C28) was increased or unchanged in soil. This result suggests that likely the occurrence of C in the mycorrhizal hyphae or the higher removal of the other alkanes increase octacosane relative concentration in soil, which more research is necessary.