Toxicity of cobalt ferrite (CoFe2O4) nanobeads in Chlorella vulgaris: Interaction, adaptation and oxidative stress

• Cobalt ferrite NBs induce severe oxidative stress & mechanical damage to algae.
• Algal exudates effectively reduce shedding of ions compared to adsorption.
• Cobalt ferrite shows different rate of ion release for Co and Fe ions.
• Interferences from cobalt ferrite NBs can be avoided by additional ultracentrifugation and additional washing steps.

The potential toxicity of CoFe2O4 nanobeads (NBs) in Chlorella vulgaris was observed up to 72 h. Algal cell morphology, membrane integrity and viability were severely compromised due to adsorption and aggregation of NBs on algal surfaces, release of Fe3+ and Co2+ ions and possible mechanical damage by NBs. Interactions with NBs and effective decrease in ions released by aggregation and exudation of algal cells as a self defense mechanism were observed by Fourier transform infrared attenuated total reflectance (FTIR-ATR) and inductively coupled plasma mass spectrometry (ICP-MS). The results corroborated CoFe2O4 NBs induced ROS triggered oxidative stress, leading to a reduction in catalase activity, activation of the mutagenic glutathione s-transferase (mu-GST) and acid phosphatase (AP) antioxidant enzymes, and an increase in genetic aberrations, metabolic and cellular signal transduction dysfunction. Circular dichroism (CD) spectra indicated the weak interactions of NBs with BSA, with slight changes in the α-helix structure of BSA confirming conformational changes in structure, hence the potential for functional interactions with biomolecules. Possible interferences of CoFe2O4 NBs with assay techniques and components indicated CoFe2O4 NBs at lower concentration do not show any significant interference with ROS, catalase, mu-GST and no interference with CD measurements. This study showed ROS production is one of the pathways of toxicity initiated by CoFe2O4 NBs and illustrates the complex processes that may occur between organisms and NBs in natural complex ecosystem.

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