The toxicity of oxidised DWCNTs to the aquatic organisms, and related causing mechanisms

Abstract

Carbon nanotubes (CNTs) find wide applications as their science and applicability are well understood. According to Lux Research Inc., the market for CNTs increased from $43 million in 2005 to $260 million by 2010. Whilst successful applications of CNTs are important for economic growth globally, there is necessity to understand their potential environmental impacts, and how such effects can be mitigated if established. Therefore, in this paper we present findings on the acute toxicity of double walled carbon nanotubes (DWCNTs) and possible mechanisms in which they cause toxic effects on: Pseudokirchneriella subcapitata (algae), Daphnia pulex (macro-invertebrates), and Poecilia reticulata (fish). The effective concentration resulting in 50% effect (EC(sub50)) of DWCNTs to P. subcapitata was 25.7 mg/L whilst the lethal concentrations (LC50) of DWCNTs to D. pulex and P. reticulata were 4.48 mg/L and 113.644 mg/L, respectively. The toxicity mechanism of DWCNTs to P. subcapitata was established to be through shading effect and agglomeration processes. Conversely, the toxicity to D. pulex and P. reticulata was through agglomeration, physical interaction (piting), and oxidative stress mechanisms – which were confirmed to be similar with mechanisms earlier reported for the three aquatic organisms in earlier scientific reports. Finally, the paper discusses the linkage between the toxicity mechanisms and the physicochemical properties of DWCNTs, namely: agglomeration state, surface chemistry, and morphology. Our findings highlight the significance of linking engineered nanomaterials toxicity to their inherent physicochemical properties. Data of this nature is useful in supporting systematic risk assessment of ENMs in the aquatic ecosystems.