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

Abstract

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 CO 2 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 + /Co 2+ 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.

Predicting the phytotoxic mechanism of action of LiCoO2 nanomaterials using a novel multiplexed algal cytological imaging (MACI) assay and machine learning

“…Furthermore, the hydrodynamic diameter of LCO also generally increases with increasing concentration, thus also suggesting increasing aggregation of LCO nanoparticles with increasing concentration. These results generally coincide with LCO's behavior in other aqueous media, like moderately hard reconstituted water 41 and Bold's modified freshwater solution, 8 as well.…”

“…Li x CoO 2 nanosheets were synthesized using techniques described in previous studies. 8,23,24 18.2 MΩ cm −1 water was used for each step during the synthesis. A (Co(OH) 2 ) precursor was prepared using a precipitation reaction between LiOH and Co(NO 3 ) 2 ·6H 2 O.…”

“…In a previous study, LCO was reported to cause a number of physiological impacts to Raphidocelis subcapitata , such as reduced growth, altered pigment biosynthesis, and impaired photosynthetic productivity. 8 Furthermore, LCO nanoparticles were proven to physically enter the algal cells, thus implying that they undergo direct interactions with key subcellular compartments. 8 However, our understanding of the mechanisms governing these consequences is still unclear.…”

“…8 Furthermore, LCO nanoparticles were proven to physically enter the algal cells, thus implying that they undergo direct interactions with key subcellular compartments. 8 However, our understanding of the mechanisms governing these consequences is still unclear. Given that photosynthesis was impacted in algae and its reverse reaction, respiration, has also been reportedly impacted in higher animal species, 6 it's likely that they may experience similar mechanistic disturbances.…”

“…Lastly, R. subcapitata was also chosen in order to make direct connections to previous algal-based LCO studies in the literature, which also used this algal species as a toxicological model organism. 8 The phenotypic profiles of LCO-treated cells were compared to several reference compounds with established MoAs to predict the phytotoxic MoA of LCO. These reference compounds were chosen to represent MoAs that have been reported for other nanomaterials like membrane disruption, 21 DNA damage, 22 and more.…”