The Effect of Metals on Biological Remediation of Munitions-Contaminated Soil

Abstract

The effects of copper, iron, lead, and zinc on the treatment procedure developed to anaerobically remove munitions compounds from contaminated soils were examined. Soil slurry reactors are fed an external carbon source to cause oxygen depletion and create anaerobic conditions, then the anaerobic degradation of munitions compounds by anaerobes present in a soil inoculum occurs. Previous experiments have shown the process to be complete by 14 days. None of the metals tested affected the creation of anaerobic conditions and anaerobic removal of TNT from contaminated soil. The removal of the intermediates of TNT metabolism, 4-amino-2,6-dinitrotoluene, and 2,4-diamino-6-nitrotoluene as well as hexahydro-1,3,5-trinitro-1,3,5,-triazine (RDX) was affected by the presence of some metals, most notably copper. Iron did not inhibit or stimulate the degradation process. Zinc (1.5 mg Zn/g soil) delayed the complete removal of the second intermediate of TNT degradation 2,4-diamino-6-nitrotoluene, by 8 days. Lead (greater than 1 mg Pb/g soil) delayed the complete metabolism of 2,4-diamino-6-nitrotoluene and RDX by as many as 9 days. The lowest concentration of copper used (4 mg Cu/g soil) completely prevented the removal of 2,4-diamino-6-nitrotoluene and RDX but not 4-amino-2,6-dinitrotoluene. Copper, at 8 and 12 mg Cu/g soil, completely prevented the removal of 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene and RDX. Key words: Anaerobic; bioremediation; munitions; soils; metals