Physiological effects of lithiated cobalt oxide nanomaterials on Selenastrum capricornutum

In this study, the model algal biological indicator, Raphidocelis subcapitata (R. subcapitata), 

was exposed to lithium cobalt oxide nanomaterials (LCO) for 48 hours.

Several physiological endpoints were recorded to evaluate the effect of LCO on exposure to RGeneral toxicological effects of subcapitata.

Considering our current understanding of the toxicological and molecular effects of LCO in other organisms, 

we hypothesize that LCO may have a negative impact on physiological aspects of algae related to growth and energy production.

Main research results:

 (1) LCO has significantly changed RThe proliferation mode and energy generation and storage mode of subcapitata algae

(2) LCO to RThe impact of subcapitata leads to a reduction in the total amount of useful chemical energy 

that it can provide to the aquatic food web network

Complex metal oxide nanomaterials, such as lithium cobalt oxide (LCO) nanosheets, are one of the most widely used nanomaterials in the market.

Their widespread use in battery storage technology has significant environmental implications, 

but there is currently insufficient infrastructure for their proper disposal and recycling, 

posing a significant risk to the health and sustainability of ecosystems.

To investigate the fitness of R. subcapitata  to the response of LCO, several endpoints related to growth and energy production were evaluated.

All the parameters tested are related to metabolism and can affect the results of the larger ecosystem.

For example, the amount of net carbon biomass produced by a single cell will determine how much energy is available to sustain its daily cell growth.

If cells become energy-deficient, they may not be able to sustain energy-intensive processes like cell division, leading them to enter a state of quiescence.

Cells in this state can grow into larger biological volumes because they lose the ability to proliferate 

and accumulate neutral lipids such as TAG due to changes in central carbon metabolism.

In our experiment, as hypothesized, the physiological aspects of algae related to growth and energy production were negatively affected by LCO.

The negative effects on growth are manifested as growth inhibition 

and a significant increase in biological volume, indicating an increase in cell cycle disorder.

The negative impact on energy production is manifested in a significant decrease 

in net carbon biomass production and a significant excess production of TAG.

However, interestingly, cells treated with the dissolved Li+/Co2+ ion control did not significantly affect any of the endpoints tested, 

suggesting that the phytotoxicity of LCO is mediated through a nanospecific mechanism rather than an ion-specific mechanism, 

for reasons that are not yet clear.

However, LCO has unique physical and chemical properties and high specific surface area, which makes the application of LCO possible.

Using an enhanced dark field microscope combined with hyperspectral imaging technology, 

we conducted a visual study of the interaction between LCO particles and algal cells. 

Within the cells treated with LCO, we observed the deposition of LCO (Figure 1F).

These LCO deposits are only visible on the same focal plane as the cells, and are not visible on their periphery, 

indicating that LCO actually enters the cells, rather than just adhering to the outer surface.

No LCO deposition was observed in the control group cells (Figure 1C).

The spectral reference library of LCO was constructed using LCO particle samples 

in algal culture medium and LCO-treated algal samples (Figure 1A).

Spectral and mapping algorithms identified pixels that matched the LCO spectrum and mapped them in red, 

thereby confirming the presence of LCO deposits in the algal cells treated with LCO (Figure 1G).

As expected, these spectra were not recognized in the control cells, resulting in no mapping (Figure 1D).

At present, the internalization mechanism is still unclear.

However, the vesicle shape of the tightly packed LCO deposits (Figure 1F) may be ingested through endocytosis.

Figure 1. (A) Lithiated cobalt oxide (LCO) spectral library.(B) A control cell and (C) a spectral image generated from LCO internalized 

from cells exposed to 1 μgmL-1 LCO.(D) Representative dark field micrographs of control cells and (E) cells exposed to 1 μgmL-1 LCO;

The red arrow points to the internalized LCO deposits.

The spectral mapping algorithm is used to identify pixels that match the LCO spectral library in (F) a control unit and (G) a unit exposed to 1 μgmL-1 LCO;

Pixels that match the LCO spectral library are mapped to red.

In summary, as engineered nanomaterials continue to be used and produced, 

it is important to better understand how they will interact with the environment and what impact they will have on ecosystem health.

We provide information about the effect of LCO nanosheets on microalgae RInsights into the initial impact of subcapitata.

The physiological effects observed in this study indicate that LCO significantly alters 

the proliferation pattern of this alga and its energy production and storage mechanisms, 

resulting in a reduction in the total amount of useful chemical energy it can provide to the aquatic food web.

However, more effort is needed to evaluate the cellular and molecular mechanisms that control these physiological effects.

Although these effects have been evaluated at the cellular level, they may have a greater impact at the ecosystem level, 

as freshwater ecosystems are entirely dependent on the ability of primary producers such as R. subcapitata to drive nutrient cycling and energy flow.

Therefore, in the future, we will develop infrastructure to appropriately and sustainably store or recycle 

this engineered nanomaterial as a means of preventing widespread contamination.