Mechanisms underlying the acute toxicity of fullerene to Daphnia magna: Energy acquisition restriction and oxidative stress

The toxicity of fullerene (C₆₀) to Daphnia magna has been a subject with increasing concerns. Nevertheless, the underlying mechanisms are still poorly understood. In the present study, we evaluated various aspects of the toxicological impacts of C₆₀ on daphnia. After a 72-h exposure, the 50% effective concentration of C₆₀ was 14.9 mg/L for immobilization, and 16.3 mg/L for mortality. Daphnia exhibited a quick uptake of C₆₀ with a body burden value of 413 μg/g in wet weight in the 1 mg/L C₆₀ treatment group. Transmission electron microscopy observations revealed that C₆₀ had mainly accumulated in the guts of organisms. The feeding rate, gut ultra-structural alterations, and digestive enzyme activities of daphnia in response to C₆₀ treatment were evaluated. The results revealed a significant reduction in the digestion and filtration rates, as well as gut impairment and inhibition of digestive enzymes (cellulose, amylase, trypsin, and β-galactosidase) activity of C₆₀ exposed daphnia. In addition, the changes in superoxide dismutase (SOD) and malondialdehyde (MDA) levels in daphnia under C₆₀ exposures were also discovered. These results, for the first time, provide systematic evidence that C₆₀ caused a restriction in energy acquisition and increased oxidative damage in daphnia, which might be related to the bioaccumulation of C₆₀ and finally led to the immobility and mortality.