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The increased use and incorporation of engineered nanoparticles (ENPs) in consumer products requires a robust assessment of their potential environmental implications. However, a lack of standardized methods for nanotoxicity testing has yielded results that are sometimes contradictory. Standard ecotoxicity assays may work appropriately for some ENPs with minimal modifications, but produce artefactual results for others. Therefore, understanding the robustness of assays for a range of ENPs is critical. In this study, we evaluated the performance of silicon, polystyrene, and gold ENPs with different charged coatings and sizes to examine in a standard Caenorhabditis elegans toxicity assay containing an Escherichia coli food supply. Of all of the ENPs tested, only those with a positively charged coating caused growth inhibition. The positively charged ENPs were observed to heteroagglomerate with Escherichia coli cells, suggesting that the ENP were impacting the ability of nematodes to feed, leading to a false positive toxic effect on C. elegans growth and reproduction. When the ENPs were tested in two alternate C. elegans assays that did not contain E. coli, we found greatly reduced toxicity of ENPs at the concentrations tested. This study illustrates one of the unexpected artifacts that can occur in nanotoxicity assays.
Environmental Science & Technology