The effects of humic acid on the uptake and depuration of fullerene aqueous suspensions in two aquatic organisms

The authors investigated the uptake and depuration of fullerene aqueous suspensions (nC₆₀) in 2 aquatic organisms: Daphnia magna and zebrafish. The effects of humic acid were examined to elucidate its possible mechanisms in the aquatic environment. The uptake was concentration-dependent in both organisms, and the maximum uptake concentration of nC₆₀ in Daphnia (2268±158mg/kg) was approximately 1 order of magnitude higher than that in zebrafish (222±30mg/kg) because of the larger gut volume ratio to the mass of Daphnia or its high uptake efficiency. Humic acid reduced the uptake of nC₆₀ in Daphnia and zebrafish as a result of the size effect and the polarity alternation of nC₆₀. The depuration patterns were rapid for Daphnia and slow for zebrafish, and the differences were most likely the result of different water exchange frequencies between organisms. The remaining nC₆₀ percentages were approximately 20% for Daphnia and 30% for zebrafish after 48-h depuration, suggesting that a large nC₆₀ burden still existed for both aquatic organisms and that there is a need for further studies on the potential for trophic transfer.