BIOACCUMULATION AND SORPTION BEHAVIORS OF POLYETHYLENEIMINE (PEI)-COATED MULTI-WALLED CARBON NANOTUBES
Elijah J. Petersen1, Roger A. Pinto2, Danielle J. Mai2, Peter F. Landrum3, Liwen Zhang4, Qingguo Huang4, Xiangyang Shi5, and Walter J. Weber, Jr. 2
1Biochemical Sciences Division, NIST, Gaithersburg, MD, 20899, USA
2Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
3National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, 4840 State Rd., Ann Arbor, MI, 48108, USA
4Department of Soil Sciences, University of Georgia, Griffin, GA, 30223
5Nanobiotechnology Laboratory, College of Chemistry, Chemical Engineering, and Biotechnology, Donghua University, Shanghai 201620, P. R. China
Determining the effects of various surface coatings on carbon nanotubes (CNTs) is critical given the numerous expected applications of CNTs and their inevitable release into ecosystems. To explore the potential ecotoxicological effects of CNT surface modifications, we modified multi-walled carbon nanotubes (MWNTs) with polyethyleneimine (PEI) coatings, which endow the nanotubes with enhanced aqueous stability and, after additional chemical modifications, positive, negative, or neutral surface charges. Uptake and elimination experiments for PEI-MWNTs with various surface charges spiked to soils revealed the same limited earthworm accumulation and ready elimination as purified MWNTs. Interestingly, PEI-MWNTs and regular MWNTs revealed significantly different sorption and desorption behaviours in soils, which contrasts with their similar, limited bioaccumulation. Conversely, Daphnia magna, an aquatic organism, accumulated substantial concentrations of PEI MWNTs and was only able to excrete them with algae feeding. This suggests that the availability of food in ecosystems will substantially affect the long-term fate of nanotubes ingested by daphnia. Quantification of the carbon nanotubes in earthworms and daphnia was performed using carbon-14 labeled nanotubes. This approach overcomes significant measurement limitations to accurately determine CNT concentrations in environmentally relevant tissues and media. Additionally, PEI coatings increased nanotube toxicity to daphnia as exhibited by elevated percentages of immobilized daphnia after exposure to identical nanotube concentrations as regular MWNTs. Significant differences were observed among the various types of nanotubes suggesting that surface coatings may strongly influence the potential ecotoxicological effects of carbon nanotubes in the environment.