Acute Toxicity of Double-Walled Carbon Nanotubes to Three Aquatic Organisms

This study investigated the toxicity of double walled carbon nanotubes (DWCNTs) to three aquatic organisms, namely,Pseudokirchneriella subcapitata,Daphnia pulex, andPoecilia reticulataunder the influence of exposure media properties specifically the ionic strength and organic matter represented by humic acid. Results indicated that ionic strength enhanced DWCNTs agglomeration whilst humic acid stabilized the CNTs and in turn inhibited the formation of aggregates. LC50s forD. pulexwere higher at 2.81 and 4.45 mg/L for pristine and oxidised DWCNTs, respectively; however,P. reticulatahad lower values of 113.64 mg/L and 214.0 mg/L for the same CNTs correspondingly.P. subcapitatahad EC50s of 17.95 mg/L and 10.93 mg/L for the pristine and oxidised DWCNTs, respectively. In the presence of humic acid high DWCNTs acute toxicity towardsD. pulexandP. reticulatawas observed but ionic strength led to opposite effect irrespective of DWCNTs form. Both humic acid and ionic strength shielded theP. subcapitatafrom toxic effects of DWCNTs. Overall, our findings suggest that the toxicity of DWCNTs in the aquatic systems (i) will be dependent on media properties and (ii) is likely to proceed at different rates to organisms at different trophic levels.