Bioaccumulation of CeO2 Nanoparticles by Earthworms in Biochar-Amended Soil: A Synchrotron Microspectroscopy Study

The interactions of nanoparticles (NPs) with biochar and soil components may substantially influence NP availability and toxicity to biota. In the present study, earthworms (Eisenia fetida) were exposed for 28 days to a residential or agricultural soil amended with 0-2000 mg of CeO2 NP/kg and with biochar (produced by the pyrolysis of pecan shells at 350 and 600 degrees C) at various application rates [0-5% (w/w)]. After 28 days, earthworms were depurated and analyzed for Ce content, moisture content, and lipid peroxidation. The results showed minimal toxicity to the worms; however, biochar (350 or 600 degrees C) was the dominant factor, accounting for 94 and 84% of the variance for the moisture content and lipid peroxidation, respectively, in the exposed earthworms. For both soils with 1000 mg of CeO2/kg at 600 degrees C, biochar significantly decreased the accumulation of Ce in the worm tissues. Amendment with 350 degrees C biochar had mixed responses on Ce uptake. Analysis by micro X-ray fluorescence (mu-XRF) and micro X-ray absorption near edge structure (mu-XANES) was used to evaluate Ce localization, speciation, and persistence in CeO2- and biochar-exposed earthworms after depuration for 12, 48, and 72 h. Earthworms from the 500 mg of CeO2/kg and 0% biochar treatments eliminated most Ce after a 48 h depuration period. However, in the same treatment and with 5% BC-600 (biochar pyrolysis temperature of 600 degrees C), ingested biochar fragments (similar to 50 pm) with Ce adsorbed to the surfaces were retained in the gut after 72 h. Additionally, Ce remained in earthworms from the 2000 mg of CeO2/kg and 5% biochar treatments after depuration for 48 h. Analysis by mu-XANES showed that, within the earthworm tissues, Ce remained predominantly as Ce4+O2, with only few regions (2-3 mu m(2)) where it was found in the reduced form (Ce3+). The present findings highlight that soil and biochar properties have a significant influence in the internalization of CeO2 NPs in earthworms; such interactions need to be considered when estimating NP fate and effects in the environment.