Abstract
Carboxylated multiwalled carbon nanotubes (MWCNTs-COOH) have become a growing concern in terms of their fate and toxicity in aqueous environments. Methane (CH4) is a major product of organic matter degradation in waterlogged environments. In this study, we determined the effect of MWCNTs-COOH on the production of CH4 from propionate oxidation in paddy soil enrichments. The results showed that the methanogenesis from propionate degradation was accelerated in the presence of MWCNTs-COOH. In addition, the rates of CH4 production and propionate degradation increased with increasing concentrations of MWCNTs-COOH. Scanning electron microscopy (SEM) observations showed that the cells were intact and maintained their structure in the presence of MWCNTs-COOH. In addition, SEM and fluorescence in situ hybridization (FISH) images revealed that the cells were in direct contact with the MWCNTs and formed cell-MWCNTs aggregates that contained both bacteria and archaea. On the other hand, nontoxic magnetite nanoparticles (Fe3O4) had similar effects on the CH4 production and cell integrity as the MWCNTs-COOH. Compared with no nanomaterial addition, the relative abundances of Geobacter and Methanosarcina species increased in the presence of MWCNTs-COOH. This study suggests that MWCNTs-COOH exerted positive rather than cytotoxic effects on the syntrophic oxidation of propionate in paddy soil enrichments and affected the bacterial and archaeal community structure at the test concentrations. These findings provide novel insight into the consequences of nanomaterial release into anoxic natural environments.
Highlights
Carbon nanotubes (CNTs) are hollow cylinders with microscale lengths and nanoscale diameters that are composed of aligned benzene rings (Iijima, 1991)
The results showed that the addition of Fe3O4 and Multi-walled carbon nanotubes (MWCNTs)-COOH increased the rate of methane production from propionate oxidation
In the first enrichments (Fig. 1A), the time preceding the completion of CH4 production was much shorter in the assays with Fe3O4 and with high concentration of MWCNTs-COOH than in the assays without nanomaterials or with low concentration of MWCNTs-COOH
Summary
Carbon nanotubes (CNTs) are hollow cylinders with microscale lengths and nanoscale diameters that are composed of aligned benzene rings (Iijima, 1991). Multi-walled carbon nanotubes (MWCNTs) are widely used due to their unique antimicrobial properties. How to cite this article Zhang et al (2018), Response of methane production via propionate oxidation to carboxylated multiwalled carbon nanotubes in paddy soil enrichments. Release of CNTs could occur at all steps in the life cycle of consumer products. Relevant release scenarios of CNTs are described in detail: injection molding, manufacturing, sports equipment, fuel system components, landfills, windmill blades, electronics, tires, textiles, and incineration (Nowack et al, 2013). CNTs fate models predict that the CNTs concentrations are between 6.6 ng/L and 18 ng/L in the plant effluent and with a modeled increase in sediment deposition rate of 40 ng/kg to 229 ng/kg per year in United States (Gottschalk et al, 2009)
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