Determining the ecotoxicity of nanodiamonds and quantum dots using the soil nematode Caenorhabditis elegans

Abstract

Engineered nanoparticles (ENP) are being used in many commercial products and applications, such as biological imaging, toothpaste and electronics. As the production, use and disposal of these products increase, environmental releases are inevitable. The environmental toxicity and mechanisms of toxicity of these particles are mostly unclear. Studies regarding these factors of ENP are necessary for sustainable growth of safety by design nanotechnology development while also protecting the environment. The aim of this project was to compare the toxicological effects of CdTe quantum dots (QDs), nanodiamonds (NDs) and nano gold (nAu) using the soil nematode Caenorhabditis elegans (C. elegans) and to relate the effects to the uptake and distribution of these particles in the organism. Physicochemical behaviour, uptake and toxicity (growth, fertility and reproduction) in the nematode C. elegans was assessed for QDs and ND with three different charged functional groups (COOH, PEG, NH3), as well as for citrate capped nAu. The wild-type (N2) C. elegans strain was used for this study and exposures were carried out in M9-media over a period of 96 h with Escherichia coli (E. coli) OP50 as food source. Internalization was only assessed for quantum dot groups since they were the only groups to display some form of response. Internalization was observed using CytoViva®, which revealed QDs within the intestine, gonads and vulva of the nematodes. Scanning electron microscopy did not successfully show internalization of particles within the cells and suggests that transmission electron microscopy would be better suited to visualize particles to assess cytotoxicity. After 96 h exposures, growth inhibition was observed from bulk metal (Cd and Te) ionic salt exposures at low mg/L levels and QD-NH3 functionalized particles at higher levels of exposure. These results indicate that ionic salts are more toxic than their nano equivalents. It also indicates that the positive charged functional groups (NH3) particles are more toxic than the neutral and negative charged functionalized QDs when assessing growth. Fertility was not significantly affected by exposures and reproduction results indicated that QDs are significantly more toxic to C. elegans than NDs and nAu. Reproduction results also indicated that the PEG functionalized group had a greater inhibitory effect on reproduction than the other particles. There was a concentration dependent toxicity for all nanoparticles assessed. Aims and objectives of this project was met, and all three hypotheses where accepted. Quantum dots were internalized by C. elegans. Metal particles were more toxic than carbonaceous ENPs and charged particles did induce more toxicity in C. elegans. These results suggest that there are possibly different modes of uptake and mechanisms of toxicity between differently charged particles and different types of nanoparticles. Thus, composition, particle coatings and sizes affect nanomaterial toxicity, these should be considered and integrated into nanomaterial production