Physiological Impacts on Raphidocelis subcapitata in Response to Lithiated Cobalt Oxide Nanomaterials

Complex metal oxide nanomaterials, like lithiated cobalt oxide (LCO) nanosheets, are among the most widespread classes of nanomaterials on the market. Their ubiquitous application in battery storage technology drives their production to rates of environmental significance without sufficient infrastructure for proper disposal/recycling, thus posing a risk to ecosystem health and sustainability. The present study assesses the general toxicological impacts of LCO when exposed to Raphidocelis subcapitata; physiological endpoints relating to growth and energy production are considered. Algal growth inhibition was significantly increased at concentrations as low as 0.1 µg ml^-1 , while exhibiting a median effect concentration of 0.057 µg ml^-1 . The average biovolume of cells was significantly enlarged at 0.01 µg ml^-1 , thus indicating increased instances of cell cycle arrest in LCO-treated cells. In addition, LCO-treated cells produced significantly less carbon biomass while significantly overproducing neutral lipid content starting at 0.1 µg ml^-1 , thus indicating interference with CO₂ assimilation chemistry and/or carbon partitioning. However, the relative abundance of chlorophyll was significantly increased, likely to maximize light harvesting and compensate for photosynthetic interference. Cells that were treated with dissolved Li⁺ /Co²⁺ ions did not significantly impact any of the endpoints tested, suggesting that LCO phytotoxicity is mainly induced through nano-specific mechanisms rather than ion-specific ones. These results indicate that this type of nanomaterial can significantly impact the way this alga proliferates, as well as the way it produces and stores its energy, even at lower, sublethal, concentrations. Furthermore, impairments to crucial cellular pathways, like carbon assimilation, could potentially cause implications at the ecosystem level. Thus, in future work, it will be important to characterize the molecular mechanisms of LCO at the nano-bio interface. Environ Toxicol Chem 2023;42:1451-1462. © 2023 SETAC.