Other Pathways

Ring-cleavage of RDX has also been shown to occur under anoxic conditions, via a route that is not initiated by denitration (Hawari et al. 2000b). This pathway was documented in biodegradation experiments carried out with municipal anaerobic sludge under measured Eh values of -250 to -300 mV. The anoxic ring-cleavage route was postulated to involve enzymatic hydrolysis of an inner C-N bond as the initial step. This was followed by ring cleavage, in which the triazinic ring was divided into two detectable products: MEDINA and bis(hydroxymethyl)nitramine. The ring-cleavage products were further degraded with eventual formation of simpler products. Halasz et al. (2002) suggested that during incubation of RDX with the above sludge, water is involved in the formation of MEDINA. Following experiments with deuterated water, they observed deuterated MEDINA products, but could not determine whether inclusion of water occurred through the initial enzymatic attack on RDX with enzymatic cleavage of the inner C-N bond or was simply caused by subsequent hydrolysis of the ring-cleavage product.

Another very different RDX-transformation pathway was suggested by Zhang and Hughes (2003) who performed experiments with crude cell extract of C. acetobutylicum and demonstrated the transformation of RDX with H2 as an electron donor. The degradation was accompanied by the formation of hydrox-ylamino compounds, analogous to the transformation of TNT. Nevertheless, this pathway was not found with whole cells, and thus not yet confirmed to be of environmental relevance.

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