Influence of carbon nanotubes on pyrene bioaccumulation from contaminated soils by earthworms

Increasing production of and application potentials for carbon nanotubes (CNTs) suggest these materials will enter soil and sediment ecosystems in significant masses in upcoming years. This may result in ecological risks, either from the presence of the CNTs themselves or, given their exceptional sorption capacities, from their effects on the fate and accumulation of concurrently present hydrophobic organic chemicals (HOCs). Here we test the influence of additions of single-walled CNTs (SWNTs) and multi-walled CNTs (MWNTs) to two different pyrene-contaminated soils on uptake of this HOC by earthworms (Eisenia foetida). The effects of nanotube additions to the soils were observed to be CNT concentration dependent, with 0.3 mg nanotubes per gram of soil having no impact, while 3.0 mg/g of SWNTs or MWNTs substantially decreased pyrene bioaccumulation from both contaminated soils. The presence of CNTs also affected pyrene elimination rates. After a 14-day exposure to pyrene-spiked soils, earthworms showed enhanced elimination rates in soils amended with 3.0 mg CNT/g but not 0.3 mg CNT/g. These results suggest that the presence of SWNTs or MWNTs in terrestrial ecosystems will have concentration-dependent effects on decreasing HOC accumulation by earthworms in a manner similar to that expected of most "hard" carbons.