Aerobic biodegradation of emerging azole contaminants by return activated sludge and enrichment cultures

Environmental Fate of the Azole Fungicide Fluconazole and Its Persistent and Mobile Transformation Product 1,2,4-Triazole

Fluconazole is a persistent and mobile pharmaceutical azole fungicide observed in natural waters globally. It does not significantly degrade via traditional wastewater treatment, resulting in likely environmental and human exposure and environmental-origin azole fungicide resistance. Indirect photochemistry is known to degrade many recalcitrant contaminants in natural waters but has not been tested for fluconazole. We systematically measured rates and identified products of the indirect photodegradation of fluconazole in genuine and synthetic surface waters with varying nitrate, bicarbonate, and dissolved organic matter using high resolution mass spectrometry. Degradation half-lives of fluconazole ranged from 2 weeks to a year, indicating indirect photochemistry is slow but competitive with other loss processes. The transformation products 1,2,4-triazole and 1,2,4-triazole-1-acetic acid were produced in 30 to 100% yield during fluconazole degradation. These products are far more resistant to indirect photochemistry than fluconazole, with half-lives for 1,2,4-triazole in the environment of between 1 and 3 years when measurable with our methods. These "very persistent very mobile" contaminants are likely formed by most pharmaceutical and agrochemical azole fungicides, are regularly detected in the US and Denmark in monitoring programs and our exposure modeling demonstrates high potential for human exposure through drinking water with uncertain health implications.

High-efficiency degradation of methomyl by the novel bacterial consortium MF0904: Performance, structural analysis, metabolic pathways, and environmental bioremediation

Methomyl is a widely used carbamate pesticide, which has adverse biological effects and poses a serious threat to ecological environments and human health. Several bacterial isolates have been investigated for removing methomyl from environment. However, low degradation efficiency and poor environmental adaptability of pure cultures severely limits their potential for bioremediation of methomyl-contaminated environment. Here, a novel microbial consortium, MF0904, can degrade 100% of 25 mg/L methomyl within 96 h, an efficiency higher than that of any other consortia or pure microbes reported so far. The sequencing analysis revealed that Pandoraea, Stenotrophomonas and Paracoccus were the predominant members of MF0904 in the degradation process, suggesting that these genera might play pivotal roles in methomyl biodegradation. Moreover, five new metabolites including ethanamine, 1,2-dimethyldisulfane, 2-hydroxyacetonitrile, N-hydroxyacetamide, and acetaldehyde were identified using gas chromatography-mass spectrometry, indicating that methomyl could be degraded firstly by hydrolysis of its ester bond, followed by cleavage of the C-S ring and subsequent metabolism. Furthermore, MF0904 can successfully colonize and substantially enhance methomyl degradation in different soils, with complete degradation of 25 mg/L methomyl within 96 and 72 h in sterile and nonsterile soil, respectively. Together, the discovery of microbial consortium MF0904 fills a gap in the synergistic metabolism of methomyl at the community level and provides a potential candidate for bioremediation applications.