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

Abstract

The objective of this study was to investigate the role of the CeO2 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 CeO2-NPs functionalized with positively charged, negatively charged, and neutral coatings. The positively charged CeO2-NPs were significantly more toxic to C. elegans and bioaccumulated to a greater extent than the neutral and negatively charged CeO2-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 CeO2-NPs. The addition of humic acid (HA) to the exposure media significantly decreased the toxicity of CeO2-NPs, and the ratio of CeO2-NPs to HA influenced Ce bioaccumulation. When the concentration of HA was higher than the CeO2-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 CeO2-NPs enter the environment and are coated with NOM.

Environmental release, fate and ecotoxicological effects of manufactured ceria nanomaterials

“…Even if free Ce(III) is toxic, release of Ce(III) from the nanoceria did not explain by itself the toxicity observed in these studies (e.g. 2,46,47 ). However, the reduction of the Ce(IV) into Ce(III) at the surface of the nanoceria correlates with the toxicity.…”

“…Negligible solubility was reported; e.g. in freshwater system over 72h, 65 in moderately hard reconstituted water for 48h 2 or in algal medium for 3 days. 46 Similarly, Röhder et al measured a low dissolved Ce concentration in different algae exposure media ranging from 0.01 to 0.11 % total Ce, and 0.47 to 1.13 % in the presence of EDTA.…”

“…1,2 Ce is among the most abundant of the rare earth elements making up approximately 0.0046% of the Earth's crust by weight (similar in abundance to Cu). 3 For example, Ce concentration in soils range from 2 to 150 mg/kg.…”

Ecotoxicity and fate of a silver nanomaterial in an outdoor lysimeter study

“…This led to a sludge-soil-ratio of 5t/ha which can be applied to agricultural used land according to the German Sewage Sludge Ordinance (AbfKlärV §6 Absatz 1 1992) within 3 years. Furthermore, the organic matter content or the texture of the test soil can have a strong influence on the toxic effect of AgNM (Collin et al 2014; Cupi et al 2015; Schlich and Hund-Rinke 2015). In the present experiment a sandy loam was used as test soil sieved ≤2 mm before the soil was filled into the lysimeters, whereas Colman et al (2013) used a mineral soil from a floodplain with a high clay content (26%) sieved to 10 mm before test start.…”

Impact of sulfidation on the bioavailability and toxicity of silver nanoparticles to Caenorhabditis elegans

“…To date, the majority of nanotoxicity studies generally and those utilizing C. elegans specifically, have focused on the effects of pristine Ag-MNPs without taking into account the effects of particle aging (Collin et al, 2014). Pristine Ag-MNPs have previously been shown to cause increased mortality, decreased growth, and decreased reproduction, as well as increased oxidative stress in C. elegans Lim et al, 2012;Meyer et al, 2010;Yang et al, 2012).…”