Microbial toxicity and characterization of DNAN (bio)transformation product mixtures

• Published in: Chemosphere (Oxford) 2016-07, Vol.154, p.499-506
• Main Authors: Olivares, Christopher I., Sierra-Alvarez, Reyes, Alvarez-Nieto, Cristina, Abrell, Leif, Chorover, Jon, Field, Jim A.
• Format: Article
• Language: English
• Subjects: 2,4-Dinitroanisole; Aliivibrio fischeri - drug effects; Aliivibrio fischeri - growth & development; Anisoles - chemistry; Anisoles - toxicity; Biotransformation; Chromatography, Liquid; Dimers; Liquid chromatography quadrupole time-of-flight mass spectrometry; Mass Spectrometry; Methane - metabolism; Microbial toxicity; Munitions; Oxidation-Reduction; Sewage - microbiology; Soil Microbiology
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2016.04.007

2,4-Dinitroanisole (DNAN) is an emerging insensitive munitions compound. It undergoes rapid (bio)transformation in soils and anaerobic sludge. The primary transformation pathway catalyzed by a combination of biotic and abiotic factors is nitrogroup reduction followed by coupling of reactive intermediates to form azo-dimers. Additional pathways include N-acetylation and O-demethoxylation. Toxicity due to (bio)transformation products of DNAN has received little attention. In this study, the toxicity of DNAN (bio)transformation monomer products and azo-dimer and trimer surrogates to acetoclastic methanogens and the marine bioluminescent bacterium, Allivibrio fischeri, were evaluated. Methanogens were severely inhibited by 3-nitro-4-methoxyaniline (MENA), with a 50%-inhibiting concentration (IC50) of 25 μM, which is more toxic than DNAN with the same assay, but posed a lower toxicity to Allivibrio fischeri (IC50 = 219 μM). On the other hand, N-(5-amino-2-methoxyphenyl) acetamide (Ac-DAAN) was the least inhibitory test-compound for both microbial targets. Azo-dimer and trimer surrogates were very highly toxic to both microbial systems, with a toxicity similar or stronger than that of DNAN. A semi-quantitative LC-QTOF-MS method was employed to determine product mixture profiles at different stages of biotransformation, and compared with the microbial toxicity of the product-mixtures formed. Methanogenic toxicity increased due to putative reactive nitroso-intermediates as DNAN was reduced. However, the inhibition later attenuated as dimers became the predominant products in the mixtures. In contrast, A. fischeri tolerated the initial biotransformation products but were highly inhibited by the predominant azo-dimer products formed at longer incubation times, suggesting these ultimate products are more toxic than DNAN. [Display omitted] •DNAN (bio)transformation products caused microbial toxicity.•3-nitro-4-methoxyaniline caused 50% inhibition to methanogens at 25 μM.•N-(5-amino-2-methoxyphenyl) acetamide was the least inhibitory compound.•Azo-dimer and trimer surrogates were of similar or greater toxicity than DNAN.•Methanogens were inhibited by putative reactive intermediates during nitro-reduction.