Toxicity of cerium oxide nanoparticles to the earthworm Eisenia fetida: subtle effects

The toxicity of cerium oxide (CeO2) nanoparticles (NPs) in soils is largely unknown. This study aimed to investigate the toxicity of three different CeO2 NPs to the earthworm, Eisenia fetida, for effects on survival (at day 28) and reproduction (at day 56), as well as bioaccumulation and histopathological effects. Eisenia fetida were exposed in standard Lufa 2.2 soil to three CeO2 NPs of different size ranges (5-80 nm), one larger particle (300 nm) and a cerium salt (ammonium cerium nitrate) over an exposure range from 41-10000 mg Ce kg(-1). Survival and reproduction were not affected by the four CeO2 particles, even at the highest exposure concentration tested. Alternatively, 10 000 mg Ce kg(-1) cerium salt affected survival and reproduction; Median lethal concentration (LC50) and effective concentration (EC50) values were 317.8 and 294.6 mg Ce kg(-1). Despite a lack of toxic effect from the different forms of CeO2 particles, there was a dose-dependent increase in cerium in the organisms at all exposure concentrations, and for all material types. Earthworms exposed to CeO2 particles had higher concentrations of total cerium compared to those exposed to ionic cerium, but without exhibiting the same toxic effect. Histological observations in earthworms exposed to the particulate forms of CeO2 did, however, show cuticle loss from the body wall and some loss of gut epithelium integrity. The data suggest that that CeO2 NPs do not affect survival or reproduction in E. fetida over the standard test period. However, there were histological changes that could indicate possible deleterious effects over longer-term exposures.