This study has shown that RDX obtained from the Holston Army Ammunition wastewater treatment plant was biodegraded by a methanogenic enrichment culture when fed reduced cosubstrates such as ethanol. RDX served as an terminal electron sink, diverting H2 away from carbon dioxide reduction, thus inhibiting methane production.
Initial studies showed mononitroso-, dinitroso-, and trinitroso-RDX intermediates. This suggests that the biodegradation pathway is similar to that reported by Kaplan et al. No transient intermediates were seen in later studies with the enrichment culture, but the same pathway is likely used. The absence of intermedates is likely due to the much lower concentration of RDX (30 _M) compared to concentrations of 80 _M or more in the initial studies of this project. More work is needed to clarify the biodegradation pathway, especially regarding products formed after reduction of the RDX nitroso-intermediates.
This study has contributed significantly to an explanation of how RDX, a nitramine explosive, is biodegraded under anaerobic conditions. Specifically, RDX is biodegraded by serving as a terminal electron acceptor, a fundamentally different mechanism than that used by bacteria for degrading other organic compounds. These findings have widespread application in wastewater treatment and cleanup technologies. Furthermore, this increased understanding of the mechanism used by bacteria to biodegrade RDX will be useful in identifying and isolating the requisite enzymes.