Sorption of Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls to Soot and Soot-like Materials in the Aqueous Environment:  Mechanistic Considerations

Abstract

Recent studies have shown that sorption of polycyclic aromatic hydrocarbons (PAHs) in soot-water systems is exceptionally strong. As a consequence, soot may fully control the actual fate of PAHs in the aquatic environment. However, sorption has only been characterized for a limited number of PAHs to diesel soot, and the mechanism is poorly understood. In this paper, we present an extensive data set of sorbent-water distribution coefficients (K(S), n = 236) for a series of PAHs (both native and added) and polychlorinated biphenyls (PCBs) to five different types of soot and five soot-like materials. Both Ks values and physicochemical properties of the sorbents show large variation. In general, sorption is very strong, with K(S) values up to 10(10), showing the highest distribution coefficients on a mass basis ever reported. Sorption of in particular PAHs is often over 1000 times as strong as sorption to amorphous sedimentary organic carbon. The variation in K(S) values cannot be explained by "soot carbon fractions" or specific surface areas of the sorbents. Instead, values for native PAHs are mostly determined by the sorbates' molar volume, and values for added PAHs and PCBs are determined by the sorbents' average pore diameter. From differences in K(S) values between native and added PAH analogues, it can be deduced that generally more than 50% (with values up to 97%) of the native PAH concentration in soot is not available for distribution to the aqueous phase. We conclude that this is caused by physical entrapment of the chemicals within the solid matrix. Furthermore, most sorbents appear to preferentially sorb PCBs with planar configurations, a phenomenon most likely driven by sorption in molecular-sized pores. Pore sorption is also concluded to be the most important sorption mechanism for added PAHs together with pi-pi interaction processes with flat aromatic sorbent surfaces. Frequently observed, slowly desorbing, resistant contaminant fractions in sediments may very well be explained on the basis of these results.

Atmospheric Concentrations and Phase Partitioning of Polycyclic Aromatic Hydrocarbons in Izmir, Turkey

“…Elemental carbon and octanol are the surrogates for the soot carbon in adsorptive partitioning, and OM in absorptive partitioning, respectively. The a EC value (62.7 m 2 g À1 ) was taken from a recent study by Jonker and Koelmans [40]. The average OM contents of PM measured in this study were 53 AE 20 and 49 AE 10% for suburban and urban sites, respectively.…”

Fragrances as new contaminants in the Venice lagoon

“…Once released into the water, sufficiently persistent FMs can evaporate into the atmosphere, sink in the sediment and finally even accumulate in biota. The octanol-water repartition constants of the 17 selected FMs range from 2.0 to more than 6.0 (Table SI1) and are comparable to those of bioaccumulating pollutants such as PAHs and PCBs (Jonker and Koelmans, 2002). However, at present the hypothesis of the bioaccumulation of the 17 FMs is still far from proven.…”

Evaluation of a Conceptual Model for Gas-Particle Partitioning of Polycyclic Aromatic Hydrocarbons Using Polyparameter Linear Free Energy Relationships

“…the geometric mean of surface areas for traffic, wood, coal, and diesel soot (i.e., 59.4, 3.6, 8.2, and 62.7 m 2 g −1 ). 53 The minimum and maximum of these surface areas were also applied in order to explore the sensitivity of the model predictions. We acknowledge that the phases considered in the present study may not be fully available for PAH partitioning due to internal mixing and kinetic limitations related to OM phase-state 54 (slow diffusion in semisolid and solid phases) and that under high relative humidity (NH 4 ) 2 SO 4 and NH 4 Cl may be present in dissolved aqueous phase and subject to liquid−liquid phase separation with OM.…”