Uptake and effects of cerium(III) and cerium oxide nanoparticles to Chlamydomonas reinhardtii

Cerium (Ce) and cerium oxide nanoparticles (CeO2 NP) are increasingly used in different applications. Upon their release into the aquatic environment, the exposure of aquatic organisms becomes likely. In this study, the uptake of CeO2 NP and Ce3+ into the wild type and cell wall free mutant of Chlamydomonas reinhardtii was examined upon short term exposure. Separation of CeO2 NP and Ce3+ not taken up or loosely bound to the cells was performed by washing algae with EDTA. Despite a concentration and time dependent increase of cellular Ce upon exposure to CeO2 NP with the maximal calculated Ce concentration corresponding to 1.1 CeO2 NP per cell, an internalization of CeO2 NP with a mean size of 140 nm in C. reinhardtii was excluded. In contrast, dissolved Ce3+ (1 and 10 mM) was taken up both in the wild type and cell wall free mutant of C. reinhardtii, with a linear increase of cellular Ce within 1-2 h and maximal cellular Ce of 6.04 × 10−4 mol Lcell−1 (wild type) and 9.0 × 10−5 mol Lcell−1 (cell wall free mutant). Based on competition with Ca2+ for Ce3+ uptake, on the comparison of the wild type and the cell wall free mutant and on inhibition of photosynthetic yield, we suggest that no efficient uptake routes for Ce3+ are available in C. reinhardtii and that a fraction of the cellular Ce in the wild type strongly sorbs to the algal cell wall.