In situ bioremediation of soils contaminated with radioactive elements andtoxic heavy metals

Two experimental plots of an agricultural land contaminated with radioactiv e elements (uranium, radium thorium) and toxic heavy metals (copper, zinc, cadmium) were treated by two different biotechnological in situ methods. Th e soil in this land was characterized by a negative net neutralization pote ntial, and the soil pH was in a slightly acidic pH range (from 4 to 5). The contaminants were located mainly in the upper soil layers (mainly in the h orizon A). Both methods were connected with the initial solubilization of the contamin ants. Water acidified with sulphuric acid was used as a leach solution. The solubilization was mainly a result of the activity of the indigenous soil microflora. This activity was enhanced by suitable changes in the levels of some essential environmental factors, such as water, oxygen and nutrient c ontent of the soil. The first method was then connected with the removal of the dissolved contaminants from the soil through the soil effluents. The s econd method was based on the transfer of the contaminants into the deeply located soil horizon B-2, where they were immobilized mainly as a result of the activity of the indigenous sulphate-reducing bacteria. Their activity was enhanced by injecting water solutions of organic compounds into the hor izon B-2 through boreholes located in the relevant experimental plot. (C) 2 001 Elsevier Science B.V. All rights reserved.