Effect of Exposure Concentration and Growth Conditions on the Association of Cerium Oxide Nanoparticles with Green Algae

The increasing release of engineered nanoparticles (NPs) into aquatic ecosystems makes it crucial to understand the interactions of NPs with aquatic organisms, such as algae. In this study, the association of CeO(2) NPs with unicellular algae (Raphidocelis subcapitata) and changes to the cellular elemental profile were investigated using three exposure concentrations (1, 50, and 1000 µg CeO(2)/L) at two different algal growth conditions—exponential and inhibited growth (1% glutaraldehyde). After a 24 h-exposure, algal suspensions were settled by gravity and CeO(2)-NP/algae association was analyzed by single-cell inductively coupled plasma quadrupole mass spectrometry (sc-ICP-QMS) and ICP time-of-flight MS (sc-ICP-TOFMS). Concurrent detection of the cellular fingerprint with cerium indicated NP association with algae (adsorption/uptake) and changes in the cellular elemental profiles. Less than 5% of cells were associated with NPs when exposed to 1 µg/L. For 50 µg/L exposures in growing and inhibited cell treatments, 4% and 16% of cells were associated with CeO(2) NPs, respectively. ICP-TOFMS analysis made it possible to exclude cellular exudates associated with CeO(2) NPs due to the cellular fingerprint. Growing and inhibited cells had different elemental profile changes following exposure to CeO(2) NPs—e.g., growing cells had higher Mg and lower P contents independent of CeO(2) concentration compared to inhibited cells.