Bioaccumulation of 14C60 by the earthworm Eisenia fetida

Abstract

Carbon fullerenes, including buckminsterfullerene (C(60)), are increasingly available for numerous applications, thus increasing the likelihood of environmental release. This calls for information about their bioavailability and bioaccumulation potential. In this study, (14)C-labeled C(60) and (14)C-phenanthrene (positive control) were added separately to soils of varying composition and organic carbon content (OC), and their bioaccumulation in the earthworm Eisenia fetida was compared. Biota-sediment accumulation factors (BSAF) were measured after 24 h depuration in soils with high C(60) dosages (60, 100, and 300 mg-C(60) kg(-1) dry soil), which exceed the soil sorption capacity, as well as in soils with a low C(60) dose (0.25 mg kg(-1)) conducive to a high fraction of sorbed molecular C(60). The BSAF value for the low-dose soil (0.427) was 1 order of magnitude lower than for less hydrophobic phenanthrene (7.93), inconsistent with the equilibrium partition theory that suggests that BSAF should be constant and independent of the K(OW) value of the chemical. Apparently, the large molecular size of C(60) hinders uptake and bioaccumulation. Lower BSAF values (0.065-0.13) were measured for high-dose soils, indicating that C(60) bioaccumulates more readily when a higher fraction of molecular C(60) (rather than larger precipitates) is available. For the high-dose tests (heterogeneous C(60) system), soil OC content did not significantly affect the extent of C(60) bioaccumulation after 28 d of incubation, although higher OC content resulted in faster initial bioaccumulation. For low-dose soils, C(60) BSAF decreased with increasing soil OC, as commonly reported for hydrophobic chemicals due to partitioning into soil OC. There was no detectable transformation of (14)C(60) in either soil or worm tissue. Overall, the relatively low extent but rapid bioaccumulation of C(60) in E. fetida suggests the need for further studies on the potential for trophic transfer and biomagnification.