Carbonaceous nanomaterials are produced in high quantities and incorporated into numerous consumer products, thus warranting hazard evaluation and risk assessment to support regulatory decisions. The current study aims to elucidate environmental fates and effects of multiwall carbon nanotubes (MWCNTs), specifically regarding their interactions with environmentally ubiquitous microorganisms including possible biomagnification through trophic transfer. The MWCNTs studied have an average length of 100 nm, and a diameter of 30-50 nm with carboxyl functional groups introduced by acid treatment, rendering the MWCNTs well dispersed and stable over time in low ionic strength aqueous media. First, MWCNTs were assayed for their separate biological effects to bacteria and the protozoan predators, P. aeruginosa and T. thermophila, respectively. Bacterial growth was assessed at MWCNT concentrations of 0.1, 1 and 10 mg/l; additionally membrane integrity and reductase activity of bacteria and protozoa were measured at these MWCNT concentrations in mineral salts medium. While no significant effects were noted at 0.1 and 1 mg/l concentration levels, the bacterial specific growth rate was approximately half that of the unamended control when cultured with 10 mg/l MWCNTs. Microscopic observations indicated extensive aggregation of P. aeruginosa cells immediately after becoming in contact with 10 mg/l MWCNTs, and further aggregation during the first few hours of the growth assay. When incubated for 24 h with 10 mg/l MWCNTs in mineral salts medium, bacterial membrane integrity appeared to be compromised based on results of propidium iodide and SYTO 9 assays; 10 mg/l MWCNTs also impaired bacterial reductase activity by 40% compared to the control. Interestingly, in the unicellular eukaryote T. thermophila, 10 mg/l MWCNTs inhibited mitochondrial reductase activity and compromised membrane integrity to a similar extent as in bacteria, possibly suggesting a common stress response to MWCNTs across pro- and eukaryotic cells. Our results indicate that the MWCNTs studied here can have harmful effects on environmentally relevant unicellular models at relatively low concentrations. Additionally, this data provides a good basis for the assessment of possible trophic transfer of MWCNTs in the prey-predator system of protozoa grazing on MWCNT-exposed bacteria.

Toxic effects of multiwall carbon nanotubes to Pseudomonas aeruginosa and its predator Tetrahymena thermophila

249th National Meeting (2015)

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