Carbon nanotubes affect the toxicity of CuO nanoparticles to denitrification in marine sediments by altering cellular internalization of nanoparticle.

Xiong Zheng,Yinglong Su,Haining Huang,Rui Wan,Yinguang Chen,Mu Li,Xu Li

doi:10.1038/srep27748

Abstract

Denitrification is an important pathway for nitrate transformation in marine sediments, and this process has been observed to be negatively affected by engineered nanomaterials. However, previous studies only focused on the potential effect of a certain type of nanomaterial on microbial denitrification. Here we show that the toxicity of CuO nanoparticles (NPs) to denitrification in marine sediments is highly affected by the presence of carbon nanotubes (CNTs). It was found that the removal efficiency of total NOX−-N (NO3−-N and NO2−-N) in the presence of CuO NPs was only 62.3%, but it increased to 81.1% when CNTs appeared in this circumstance. Our data revealed that CuO NPs were more easily attached to CNTs rather than cell surface because of the lower energy barrier (3.5 versus 36.2 kT). Further studies confirmed that the presence of CNTs caused the formation of large, incompact, non-uniform dispersed, and more negatively charged CuO-CNTs heteroaggregates, and thus reduced the nanoparticle internalization by cells, leading to less toxicity to metabolism of carbon source, generation of reduction equivalent, and activities of nitrate reductase and nitrite reductase. These results indicate that assessing nanomaterial-induced risks in real circumstances needs to consider the “mixed” effects of nanomaterials.

Highlights

IntroductionTo date, it is largely unknown whether the coexistence of different nanomaterials could affect the toxicity of single nanomaterial to microbial denitrification in marine sediments
The concentration of nitrate was significantly higher in the CuO NPs tests than in the control (p < 0.05), which indicated that the reduction of nitrate was significantly inhibited by CuO NPs
When 50 mg/g of CNTs were present in the CuO NPs system, the final nitrate concentration, compared with single CuO NPs, was remarkably decreased from 102.6 to 72.9 mg/L, which was further declined to 52.4 mg/L with the increase of CNTs to 200 mg/g

Summary

Introduction

To date, it is largely unknown whether the coexistence of different nanomaterials could affect the toxicity of single nanomaterial to microbial denitrification in marine sediments. Once CNTs and CuO NPs co-existed in the environment, their potential environmental risks remain unclear. We report the potential effects of CuO NPs, CNTs, and CuO NPs + CNTs on denitrification in marine sediments. The mechanisms for the different toxicities of single (CuO NPs or CNTs) and mixed (CuO NPs +CNTs) nanomaterials to microbial denitrification were explored by analyzing interacting energy, nanomaterial property (including particle polydispersity index, fractal dimension, and electrical property), cell cytoplasm density, carbon source metabolism, reduction equivalent generation, and key enzymes activities. The data from this work show the importance of the “mixed” effects of nanomaterials in real circumstances, when we assess the nanomaterial-induced environmental risks

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Conclusion