Cu and Cr enhanced the effect of various carbon nanotubes on microbial communities in an aquatic environment

Environmental impacts of carbon nanotubes (CNTs) arise both from the characteristics of CNTs as well as from their sorbed contaminants from aquatic environments. In this work, we employed pristine, carboxyl-, hydroxyl- and amino-functionalized multi-walled CNTs and pristine single-walled CNTs to quantify and compare their impacts on aquatic microbial communities in the absence and presence of Cu or Cr. Aliquots of samples were set up to 10 and 40 days for culture-dependent analyses, namely, quantitative real-time polymerase chain reaction and denaturing gradient gel electrophoresis. Results revealed that the presence of CNTs or the mixture of CNTs and metals transiently affected microbial communities, and toxicity of CNTs was enhanced with the addition of metals. Meanwhile, functionalized CNTs exhibited stronger toxicity. The major impacts were observed after 10 days of exposure, but the microbial community could recover at 40 days to some extent. Though microbial communities recovered, total microbial numbers continued to decrease with contact time. Analysis of sequence cloned 16S rDNA indicated that Bacillus sp. and Acidithiobacillus sp. were the dominant taxa. Overall, CNTs would have more serious risk to an ecosystem in the presence of metals.