In situ bioremediation of soil contaminated with oil and heavy metals.

An experimental plot of soil contaminated with crude oil and heavy metals (copper, zinc and cadmium) was subjected to bioremediation using the activity of the indigenous soil microflora. The oil was light, rich in paraffins and with a very low content of asphaltene-resinous substances. Copper, zinc and cadmium were present mainly as sulfide minerals but also in forms more amenable to biological and chemical leaching. Their contents in the soil exceeded approximately 1.5-3 times the relevant permissible levels. The soil microflora contained different oil-degrading and metal-solubilizing microorganisms. The activity of this microflora was enhanced by suitable changes in the levels of some essential environmental factors such as oxygen, water and nutrient contents in the soil. The oil content in the plot was decreased from the initial 12.50 g/kg dry soil to 1.25 g/kg dry soil within 8 months of treatment. Simultaneously, the contents of copper, zinc and cadmium were decreased below the relevant permissible levels for soil of such type.