Fate and Transport of Single Walled Carbon Nanotubes in a Wetland Mesocosm

Overview: 

We have conducted the first study addressing the fate and transport of single walled carbon nanotubes (SWNT) in a highly complex terrestrial/aquatic ecosystem. We have utilized tightly controlled and highly instrumented wetland ecosystems (i.e. mesocosms) located in the Duke Forest, Durham, NC. The experimental design was configured to study the impact of nanomaterials on a complex ecosystem and to address questions including fate and transport, effect on community structure, effects on biogeochemical function and effects on productivity of the ecosystem. In Summer 2010, one mesocosm was amended with gum arabic (GA)-coated CoMoCat SWNT (c SWNT,0 = 2.5 mg L-1 in 0.5% GA). The distribution of CoMoCat SWNT in the mesocosm was followed during 8 months. Samples from representative biotic and abiotic compartments were analyzed to evaluate the transport and fate of SWNT in the ecosystem.

SWNT were quantified in organism and sediment extracts using near-infrared fluorescence spectroscopy (NIRF). This technique can be used to quantitatively detect SWNT in sediment, water, and biotic samples at environmentally relevant concentrations (lower ng ml-1 range) and qualitatively characterize SWNT samples before and after the studies. Results indicated that concentrations of CoMoCat SWNT within the water column attenuated rapidly, with near total disappearance observed within a period of 2 days (Cw,t/Cw,0 < 0.01) after spiking.  A corresponding increase of SWNT concentration in sediment traps (n=1) was observed over a period of 30 days revealing that loss of SWNT from the water column was likely due to association with sediment surfaces. The analysis of sediment core sections revealed that CoMoCat SWNT were deposited within surficial aquatic mesocosm sediments.  SWNT could not be detected in mescosm biota, indicating that minimal accumulation of SWNT occurred in these biota over a period of 8 months.  Overall, the results from our mesocosm study are consistent with literature reports describing the high particle-reactivity of SWNT.  Based on these data, SWNT can be expected to associate strongly with suspended and bedded sediments after release into the aquatic environment.