Multi-walled carbon nanotubes, natural organic matter, and the benthic diatom Nitzschia palea: “A sticky story”

Abstract

Different effects of multi-walled carbon nanotubes (MWCNTs) on the freshwater diatom Nitzschia palea were examined. MWCNTs used in this study (MWCNT) were dispersed either by sonication without (MWCNT_sonicated) or with a realistic concentration (10 mg L⁻¹) of Natural Organic Matter (MWCNT_+NOM). A pocket-size device was designed to distinguish shading effect (using MWCNT suspensions as external filters) from total exposure effect of MWCNT_sonicated and MWCNT_+NOM on benthic algae. This study demonstrates that cell division was strongly inhibited after a 48 h exposure to MWCNT_+NOM compared to MWCNT_sonicated. This device did not yield a quantifiable contribution of shading to growth inhibition of MWCNT_sonicated and below 10 mg L⁻¹ of MWCNT_+NOM. In all cases, neither lethal effects nor drops in photosynthetic quantum yield were observed. After a 6-d exposure, a complete growth recovery was observed for all conditions except at the highest concentration of MWCNT_+NOM. Different microscopic approaches using carbohydrates markers revealed the strong affinity between MWCNT and extracellular polymeric substances (EPS) produced by N. palea. These seem to constitute a defensive mechanism against MWCNT.

• Algae
• extracellular polymeric substances
• nano-ecotoxicology
• nanoparticles
• toxicity

Acknowledgements

We thank the Lacq Research Group (Arkema France) for supplying MWCNT suspensions. Part of the present study was achieved in the framework of the public/private joint research laboratory NAUTILE (NAnotUbes et écoToxIcoLogiE; Arkema France–CNRS/INPT/UPS). We acknowledge the Common Service for Transmission Electron Microscopy and Scanning Electron Microscopy of the University Paul Sabatier and Stephane Du Plouy for his help. The English language of the manuscript has been corrected by the native English Rashard Khadaroo (Université Paul Sabatier, Toulouse, France).

Declaration of interest

This research was supported by the French Ministry of higher education and research. The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.