The responses of Ceriodaphnia dubia toward multi-walled carbon nanotubes: Effect of physical–chemical treatment Original Research Article

The influence of physical–chemical treatment, e.g. ozonation (O), ultrasound (US) and mechanically dispersion, on the response of fresh water organisms, exemplified by Ceriodaphnia dubia toward multi-walled carbon nanotubes (MWCNT) was studied. Results indicated that physical–chemical treatment had pronounced effect on the stability and aggregation of carbon nanomaterials and thereby impact on C. dubia. US-MWCNT exerted the greatest toxicity to C. dubia compared to the untreated and the ozone treated MWCNT which exhibited a LC50 at one order of magnitude greater than that of US-MWCNT. Similar toxic results were observed in the 3-brood reproduction and sub-lethal growth tests. The primary diameter of MWCNT did not exhibit significant toxic impacts on C. dubia at least measured in terms of LC50. C. dubia ingested and accumulated the nanoparticles in the digestive tract and brood chamber. Upon transferring to nanoparticle-free environment, the C. dubia began to defecate the CNT particles, indicating the capability of self-cleaning. US-MWCNT was retained in the digestive tract for a longer time and also required a longer time to be cleaned than O-MWCNT. Results confirmed the importance of physical–chemical treatment on the interactions between the nanomaterials and aquatic organisms in assessing the fate, transport, and ecological impacts of nanomaterials.