RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine) Biodegradation in Aquifer Sediments under Manganese-Reducing Conditions

A shallow, RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)-contaminated aquifer at Naval Submarine Base Bangor has been characterized as predominantly manganese-reducing, anoxic with local pockets of oxic conditions. The potential contribution of microbial RDX degradation to localized decreases observed in aquifer RDX concentrations was assessed in sediment microcosms amended with [U-¹⁴C] RDX. Greater than 85% mineralization of ¹⁴C-RDX to ¹⁴CO₂ was observed in aquifer sediment microcosms under native, manganese-reducing, anoxic conditions. Significant increases in the mineralization of ¹⁴C-RDX to ¹⁴CO₂ were observed in anoxic microcosms under NO₃-amended or Mn(IV)-amended conditions. No evidence of ¹⁴C-RDX biodegradation was observed under oxic conditions. These results indicate that microbial degradation of RDX may contribute to natural attenuation of RDX in manganese-reducing aquifer systems.