Facilitated Transport of 2,2′,5,5′-Polychlorinated Biphenyl and Phenanthrene by Fullerene Nanoparticles through Sandy Soil Columns

Abstract

The potential environmental implications of buckminsterfullerene (C60) and its derivatives have received much attention. In this study, we investigated facilitated transport of 2,2',5,5'-polychlorinated biphenyl (PCB) and phenanthrene by nC60 (a stable aqueous-phase aggregate of C60) through two sandy soil columns. We found that low-level (from 1.55 to 12.8 mg/L) nC60 could significantly enhance the mobility of PCB and phenanthrene. However, none of the three model dissolved organic matters (DOMs)-a humic acid, a fulvic acid, and a bovine serum albumin-had a noticeable effect on the transport of PCB when these DOMs were present at concentrations equivalent to approximately 10-11 mg/L organic carbon. We propose that the contaminant-mobilizing ability of nC60 is a result of irreversible adsorption of a fraction of nC60-associated PCB/phenanthrene (whereas DOM-associated PCB is readily desorbable). Additionally, slow desorption kinetics of nC60-adsorbed PCB/phenanthrene is another possible mechanism. The findings in this study indicate that nC60 in the subsurface environment can greatly enhance the mobility of nonionic, highly hydrophobic organic contaminants, which typically exhibit very low mobility. Such effects should be taken into account when assessing the potential environmental risks of engineered carbonaceous nanomaterials.

Contaminant‐mobilizing capability of fullerene nanoparticles (nC60): Effect of solvent‐exchange process in nC60 formation

“…For example, under typical environmental conditions, highly hydrophobic organic contaminants, such as polychlorinated biphenyls and polycyclic aromatic hydrocarbons, sorb strongly to soil organic matter and therefore have very limited mobility in subsurface environments. In a recent study [16], we observed that trace amounts of nC 60 (less than 2 mg/L) resulted in the breakthrough of 2,2 0 ,5,5 0 -polychlorinated biphenyl (PCB) and phenanthrene through saturated soil columns within a few pore volumes (PVs), which vastly differed from what was expected based on conventional theories in that such significant transport enhancement of PCB or phenanthrene should not occur unless the concentrations of colloidal materials are very high (on the order of several hundred mg/L or higher) [18]. Thus, it is evident that the contaminant-mobilizing capability of nC 60 is far greater than those of natural colloids, such as dissolved organic matter.…”

“…Column experiments were conducted using a previously developed protocol [16]. Soil was dry-packed into Omnifit borosilicate glass columns (10 Â 0.66 cm; Bio-Chem Valve) with 10-mm stainless-steel screens (Valco Instruments) on both ends.…”

“…Then PCB stock solution in methanol was added with a microsyringe to give a total PCB concentration of approximately 11 mg/L in each working nC 60 suspension. The vials were sealed with Teflon-lined screw caps and tumbled end over end at 0.001 g for 7 d; our previous study showed that adsorption equilibrium could be reached in 3 d [16]. Afterward, 3 ml of the suspension in each vial was taken to measure the nC 60 concentration and the total PCB concentration.…”

“…In addition to being water stable and even eliciting biological response(s) [4][5][6], nC 60 can significantly enhance the transport of highly hydrophobic organic contaminants, due to the strong adsorption of contaminants to nC 60 [16,17]. Such cotransport of organic contaminants could increase exposure volumes and thus potential risk.…”

“…Thus, it is evident that the contaminant-mobilizing capability of nC 60 is far greater than those of natural colloids, such as dissolved organic matter. The surprisingly high contaminant-mobilizing capability of nC 60 compared with conventional dissolved organic matter is likely attributable to surface enthalpies of interaction and the unique porous structures of nC 60 , which result in both enhanced adsorption affinity and desorption irreversibility [16,19]. Thus, physicochemical factors that affect the structural properties or the effective surface chemistries, or both, of nC 60 might also affect nC 60 -contaminant interactions and consequently, nC 60 's capability of enhancing contaminant transport [20].…”