Thousands of nanotech-enabled products are now on the market; and those based on carbon and cellulose are found in everything from high-strength composites to plastic packaging. So it’s not surprising that a large number of research efforts are looking at the potential impact of releasing these materials into the environment. In a paper published in the latest issue of Carbon [DOI: 10.1016/j.carbon.2016.03.041], researchers have evaluated the effect of a range of nanomaterials on the health of different fish species.
The team focused on two classes of materials – (1) single-walled carbon nanotubes (SWCNTs), whose electrical, thermal and mechanical properties has seen them proposed for numerous applications, and (2) cellulose nanocrystals (CNCs), which are biodegradable, and can be manufactured from both bacteria and plants. For the fish, they selected several cells lines of Channel Catfish to act as the in vitro testbed. For their in vivo studies, they used Zebrafish embryos, which, genetically-speaking, share many features with humans.
To investigate the potential toxicological effects of SWCNTs to these organisms, some of the tubes were functionalised with carboxylic acid, while others were wrapped in lignin – a waste product from the paper industry. Zebrafish embryos were exposed to these materials throughout their development, from the gene expression stage, through to the hatching and survival stages. Results showed that the presence of functionalized SWCNTs led to higher mortality rates and delays in hatching.
The effect of carboxylated CNCs on both Zebrafish embryos and Channel Catfish was less clear cut. For in vitro studies, CNCs were found to display low cytotoxicity in all but one cell line, where CNC exposure decreased its viability. But for in whole-animal studies, no effect was seen, indicating that there was little correlation between in vivo and in vitro studies.
While these results suggest caution on the use of functionalised nanomaterials, many questions remain. The mechanism behind these results has not yet been directly established, and the concentrations involved were considerably higher than would ever be present in the environment. Given the growing use of nanomaterials, there is a clear need for more representative research – an investigation into the effect that long-term, low concentration exposure could have on aquatic life.
-- L.C. Felix, J.D. Ede, D. A. Snell, T.M. Oliveira, Y. Martinez-Rubi, B. Simard, J.H.T. Luong, G.G. Goss, “Physicochemical properties of functionalized carbon-based nanomaterials and their toxicity to fishes”, Carbon 104 (2016) 78–89. DOI: 10.1016/j.carbon.2016.03.041