Combined effects of aqueous suspensions of fullerene and humic acid on the availability of polycyclic aromatic hydrocarbons: evaluated with negligible depletion solid-phase microextraction

Abstract

The wide application of engineered carbon nanomaterials, such as fullerene (C60), will inevitably result in their introduction into the aqueous environment. Interactions of C60 with abundant natural organic matter (NOM) will likely alter the bioavailability of organic compounds to aquatic organisms. The availability of 12 types of polycyclic aromatic hydrocarbons (PAHs) in various aqueous suspensions of fullerene (nC60) prepared by different methods, e.g., in humic acid (HA) and particularly in combined systems of nC(60) and HA, was investigated by negligible depletion solid-phase microextraction (nd-SPME). The results showed that HA accelerated the rate constants (k2) of almost all PAH uptakes to the nd-SPME fibers compared with the solutions without the matrix; the combined matrices of nC(60) and HA significantly promoted the k2 of highly hydrophobic PAHs (logKOW 5.81-6.20), whereas they retarded that of less hydrophobic ones (logKOW 3.82-4.63) (p<0.05). Remarkable or minor reduction of free concentration of PAH was observed in the combined system of nC(60) and HA depending on the properties of individual PAHs. Sorption coefficients (KHA, K(C60) and K(C60+HA)) of various PAHs in different matrices were provided, and matrix concentrations showed no significant effects. For highly hydrophobic PAHs (logKOW 5.16-6.20), the logK(C60+HA) >= logKHA > logK(C60), whereas for less hydrophobic PAHs (logKOW 3.8-4.63), the Kmatrix values in various matrices showed no noticeable trend. In addition, higher K(C60) values were obtained for aqu/nC(60) than for son/nC(60) for most highly hydrophobic PAHs. The above results suggest that hydrophobicity plays an important role in determining Kmatrix in addition to the matrix effects. The interactions between nC(60) and HA have critical or minor impacts on availability, and thus bioavailability, of PAHs. This paper contributes to the understanding of the bioavailability mechanisms of organic pollutants in the aquatic environment with both nC(60) and NOM.

Keywords: Availability; Fullerene aqueous suspensions; Humic acid; Negligible depletion solid-phase microextraction; Polycyclic aromatic hydrocarbon; Sorption.