Phytoremediation of crude oil contaminated soil using glycine max (Merril); through phytoaccumulation or rhizosphere effect?

Abstract

The aim of this study was to evaluate the process which Glycine max (soybean) uses in the phytoremediation of crude oil contaminated soil. A screen house experiment was conducted with different amounts (25g, 50g and 75g) of crude oil-contaminated soil for 110 days. The initial and final total petroleum hydrocarbon (TPH) contents of the contaminated soils and that in the plant tissues were measured and the bacterial loads and types in the soil samples were determined at the end of the study. The soil pH, moisture and organic matter contents were also determined every 21 days for 110 days. Soil samples for the above analyses were obtained from the soils treated with the various amounts of crude oil with and without G. max (which served as the control). The investigation revealed that the initial TPH values of the soils were higher than the final TPH values and that there were lower TPH values in the soils with G. max compared to soils without G. max. The growth of G. max led to 52.48% reduction against 50.15% reduction in non-vegetated soil, 66.93% reduction against 44.57% reduction in non-vegetated soil and 49.04% reduction against 44.31% reduction in soil contaminated with 25g, 50g and 75g crude oil respectively The bacterial load, pH, moisture content and the organic matter contents of the crude oil contaminated soil were significantly affected by the growth of G. max at different levels of significance (P<0.05; P<0.01; P<0.001). The results of this study have shown that the growth of G. max on crude oil contaminated soil reduces the TPH level, enhances bacterial growth, improves the soil pH and improves the moisture content (for high level contamination). Thus, it is suggested that G. max is a good candidate for remediating crude oil contaminated soil and that it remediates crude oil contaminated soils through rhizospheric effect.