Comprehensive review on deciphering the biodegradation of nitramine explosives RDX and HMX: An insight on the mechanisms, pathways and environmental implication

The persistence and complex molecular structure of nitramine explosives such as RDX and HMX makes it difficult for their degradation. Increase in the number of military establishments has led to leaching and percolation of these explosives into soil and groundwater causing serious effects to the ecosystem. Over the years, extensive research has been focused on understanding toxic effects of these explosives on humans, animals and plants. However, an integrated understanding of their biodegradation by both micro and macroorganisms remained limited and unexplored. This review summarizes the recent advances in microbial degradation of RDX and HMX, emphasizing the comparative mechanisms and enzymatic pathways proposed till-date. It further focuses on the efficiency of macroorganisms including plants and mushrooms in the remediation process either individually or in synergism with biological interactions. Emerging biotechnological strategies such as bioformulation, substrate cometabolism and metabolomics based pathway elucidation are also employed for understanding their role in enhancing the degradation process. By connecting the pilot scale studies with in situ applications, this review outlines transition of bioremediation from laboratory research to field scale implementation. It highlights the sustainable approaches employed for the remediation of environment contaminated with RDX and HMX. The review also underlines the key limitations on the restriction of effective field-scale application of RDX and HMX biodegradation and provides hypothetical recommendations for future research prospects focusing on advanced treatment strategies and in-situ remediation technologies.