Toxicity And Its Mechanisms Of Carbon Nanotubes To Chlorella Sp.

With increasing production and application, carbon nanotubes (CNTs) are likely to present in the aquatic environment and thereby potentially threaten aquatic organisms with toxic mechanisms remaining in controversy. This study systematically investigated toxicities of three multiwalled CNTs (MWCNTs) to a green alga (Chlorella sp.), with a focus on examination and quantification of contributions of five possible underlying mechanisms to the algal growth inhibition. Some valuable research results are obtained.(1) MWCNTs exerted a strong inhibition on algal growth under light or dark condition and their inhibitory effects were dose-dependent. The96h IC50values of MWCNTs under light condition were41.0±3.0,12.7±0.2and12.4±0.7mg/L for MWCNT10(outer diameter:9±2nm), MWCNT40(outer diameter:28±6nm) and MWCNT100(outer diameter:70±9nm), respectively.(2) The algal toxicity of MWCNTs could mainly be explained by the three major mechanisms of shading effect, physical interaction, and oxidative damage. The contributions of metal catalyst residues in the MWCNTs and MWCNT adsorption of nutrient elements to the algal growth inhibition were negligible.(3) The contributions of the three major mechanisms to the algal toxicity of MWCNTs, which were dependent on MWCNT size and concentration, were quantitatively analyzed. The contribution of oxidative damage of MWCNT10was higher than that of MWCNT40or MWCNT100and it decreased with increasing MWCNT dose, whereas the contribution of physical interaction was positively related to the MWCNT concentration. At the concentrations around96h IC50values of the MWCNTs, the oxidative stress could account for the algal growth inhibition by about50%, while the physical interaction and the shading effect took about30%and20%of the responsibility for the algal toxicity, respectively.