Chronic toxicity of double-walled carbon nanotubes to three marine organisms: influence of different dispersion methods

Aim: Double-walled carbon nanotubes (DWNTs) are found in a variety of consumer products, but there are no ecotoxicity data of DWNTs into marine organisms. Materials & methods: Chronic toxicity of DWNTs was investigated with the diatom Thalassiosira pseudonana, copepod Tigriopus japonicus and medaka Oryzias melastigma. DWNTs were dispersed using sonication (so-DWNTs) and stirring (st-DWNTs) for comparison. Results: The median aggregation size (0.89 mu m(2)) of so-DWNTs was smaller than that of st-DWNTs (21.8 mu m(2)). Exposure to DWNTs led to growth inhibition of T. pseudonana with EC(50)s of 1.86 and 22.7 mg/l for so- and st-DWNTs, respectively. Population growth of T. japonicus was reduced to 0.1 mg/l for so-DWNTs and 10 mg/l for st-DWNTs. Growth inhibition in O. melastigma was observed at 10 mg/l for so-DWNTs but not for st-DWNTs. Conclusion: Given that so-DWNTs are consistently significantly more toxic than st-DWNTs, dispersion method and size of aggregations should be considered in DWNT toxicity testing.