Degradability of aged aquatic suspensions of C60 nanoparticles

While studies of the potential human and environmental effects of C60 and its derivatives are emerging in the scientific literature, the environmental fate of C60 is still largely unknown. In this study, aged aqueous suspensions of C60 (nC60) were investigated in the respirometric OECD test for ready biodegradability. Two suspensions of nC60 were prepared by stirring and aged under indirect exposure to sunlight for 36 months, which resulted in relatively stable suspensions with a dark-brown colour. The suspended nC60 could not be extracted into toluene and indicating that the particles were no longer present as underivatised nC60 but had undergone a transformation. TEM images and particle tracking analysis showed that the suspension consisted of particle aggregates with a size of 156 nm (SD=54nm) and 139nm (Sd=49), respectively, but also contained smaller aggregates. Samples of the nC60 suspensions (approx. 20 mg/l) were inoculated with activated sludge (30 mgTSS/L) and incubated in a mineral medium under aerobic conditions for 28 days. After 28 days no mineralization of nC60 was observed. This was not due to inhibition of the biomass, since addition of 5 mg/L sodium acetate was completely mineralized within a few days. Even with this additional carbon source no mineralization of nC60 was observed after an additional 20 days. Based on these results, aged nC60 can be classified as not ready biodegradable according to the OECD test procedure.