Influence of Natural Organic Matter and Surface Charge on the Toxicity and Bioaccumulation of Functionalized Ceria Nanoparticles in Caenorhabditis elegans

摘要

The objective of this study was to investigate the role of the CeO_2 nanoparticle (NP) surface charge and the presence of natural organic matter (NOM) in determining bioavailability and toxicity to the model soil organism Caenorhabditis elegans. We synthesized CeO_2-NPs functionalized with positively charged, negatively charged, and neutral coatings. The positively charged CeO_2-NPs were significantly more toxic to C. elegans and bioaccumulated to a greater extent than the neutral and negatively charged CeO_2-NPs. Surface charge also affected the oxidation state of Ce in C. elegans tissues after uptake. Greater reduction of Ce from Ce (Ⅳ) to Ce (Ⅲ) was found in C. elegans, when exposed to the neutral and negatively charged relative to positively charged CeO_2-NPs. The addition of humic acid (HA) to the exposure media significantly decreased the toxicity of CeO_2-NPs, and the ratio of CeO_2-NPs to HA influenced Ce bioaccumulation. When the concentration of HA was higher than the CeO_2-NP concentration, Ce bioaccumulation decreased. These results suggest that the nature of the pristine coatings as a determinant of hazard may be greatly reduced once CeO_2-NPs enter the environment and are coated with NOM.