Biotic and abiotic strategies for insensitive munitions compounds remediation

Abstract

Insensitive munitions compounds (IMCs), such as 2,4-dinitroanisole (DNAN) and 2-nitro-1,2,3-triazol-5-one (NTO), are ingredients of new munitions formulations being deployed by the military due to their lower risk of unintended explosions. Environmental contamination by IMCs can occur via industrial wastewater discharge into water bodies and pieces of undetonated ordnance on the soil, which can be dissolved by precipitation and reach ground and surface waters. The remediation of these pollutants is imperative to environmental protection since they and their reduced daughter products are toxic and potentially mutagenic. This Ph.D. thesis presents novel biotic and abiotic strategies for IMCs remediation. (i) Firstly, we show that both DNAN and NTO can be anoxically reduced by FeS minerals commonly present in soils and aquatic sediments, such as mackinawite, to their corresponding amines. The reduction process is surface-mediated. (ii) After that, we present the unusual biological process of NTO respiration. A highly-enriched culture composed mainly of Geobacter anodireducens (89.3%) and Thauera sp. (5.5%) could grow reducing NTO to 3-amino-1,2,4-triazol-5-one (ATO) while oxidizing acetate to CO2. The process was linked to ATP production, constituting evidence for NTO respiration. (iii) Then, we explored the biotic and abiotic reactions leading to the removal of 2,4-diaminoanisole (DAAN), the reduced daughter products of DNAN, in biological sludge exposed to different electron (e-) acceptor conditions: without added e- acceptor, without added e- acceptor amended with pyruvate, with nitrate, with sulfate, and with oxygen. We observed that DAAN removal in sludge was faster under oxygen exposure, with the contribution of abiotic DAAN autoxidation. A culture with 85% of unclassified microorganisms (according to a 16S rRNA sequencing) could be enriched to remove DAAN under aerobic conditions, but not under anaerobic conditions. (iv) Finally, we unveiled the mechanisms leading to the disappearance of DAAN into the natural organic matter, a phenomenon observed by previous works. We tested DAAN reactions with quinone model compounds and developed a new method to stop these fast reactions, capturing fleeting intermediates for analysis. The reactions involving DAAN and quinones were Michael addition, imine formation, and azo bond formation. An oligomerization process was responsible for capturing DAAN into humic-like insoluble substances. Overall, our results can be applied to develop biotic and abiotic remediation strategies to clean up training ranges, treat wastewater contaminated with DNAN and NTO, and assess DNAN and NTO natural attenuation.