Sorption of Polycyclic Aromatic Hydrocarbons to Oil Contaminated Sediment:  Unresolved Complex?

Abstract

Oil is ubiquitous in aquatic sediments and may affect partitioning and bioavailability of hydrophobic organic chemicals (HOCs). In contrast to other sedimentary hydrophobic carbon phases (natural organic matter, soot-like materials), oil residues have hardly received any attention as far as it concerns effects on HOC sorption. This paper describes experimental work dealing with such effects of oil on polycyclic aromatic hydrocarbon (PAH) sorption to sediments. Three different oils were spiked to a marine sediment in concentrations between 0 and 100 g/kg. Sediment-water distribution coefficients (Kd) for six deuterated PAHs were then determined either directly after spiking the oil or after a semi-natural weathering process in the lab (lasting for more than 2 yr). Resulting Kd values demonstrated sorption-reducing (competitive) effects at relatively low oil concentrations and sorption-enhancing effects at high oil concentrations. The latter effects only occurred above a certain threshold [i.e., ca. 15% (w/w) of oil on a sedimentary organic carbon basis] marking the oil concentration at which the hydrocarbon mixture presumably starts forming separate phases. Assuming a two-domain (organic carbon + oil) distribution model, oil-water distribution coefficients (K(oil)) for PAHs were estimated. For fresh oils, log K(oil) values appeared to be very similar for different types of oils, proportional to log K(OW) values and indistinguishable from log K(OC) values. For weathered oils, K(oil) values were also rather independent of the type of oil, but the affinity of low molecular weight PAHs for weathered oil residues appeared to be extremely high, even higher than values reported for most types of soot. Because affinities of high molecular weight PAHs for oils had not changed upon weathering, sorption of all PAHs studied (comprising a log K(OW) range of 4.6-6.9) to the weathered oil residues appeared to be more or less constant (averaged log K(oil) = 7.0 +/- 0.24). These results demonstrate that it is crucial to take the presence of oil and its weathering state into account when assessing the actual fate of PAHs in aquatic environments.

Toxicity of sediment-associated unresolved complex mixture and its impact on bioavailability of polycyclic aromatic hydrocarbons

“…Mehler et al [16] noted possible changes in sorptive ability of activated carbon to PAHs during the course of conducting a whole-sediment toxicity identification evaluation test, and speculated that the ineffectiveness of the carbon treatment was caused by the co-existence of sediment-associated UCM, with similar reports found by the U.S. Environmental Protection Agency (USEPA) [17]. Moreover, UCM was also reported to be persistent in sediment for decades [21] and may act as a sedimentary super-sorbent for PAHs and polychlorinated biphenyls [18][19][20].…”

“…The CH sediment was spiked with 1 g/g dw of each PAH and various levels of mineral oil (0, 0.01, 0.1 and 0.5% dw) in order to investigate the impact of UCM on bioaccumulation of sediment-associated PAHs to L. variegatus. The three PAHs were spiked as a mixture for these tests and the concentrations of PAHs and mineral oil were selected because they were environmental relevant [16,20]. The spiked sediments were aged at 4 • C for 14 d before conducting the bioaccumulation testing in triplicate following USEPA protocols [22].…”

“…In addition to its own bioaccumulation potential and toxicity, UCM may also alter the bioavailability and toxicity of other contaminants in sediment [16][17][18][19][20]. Mehler et al [16] noted possible changes in sorptive ability of activated carbon to PAHs during the course of conducting a whole-sediment toxicity identification evaluation test, and speculated that the ineffectiveness of the carbon treatment was caused by the co-existence of sediment-associated UCM, with similar reports found by the U.S. Environmental Protection Agency (USEPA) [17].…”

Extraction of sediment‐associated polycyclic aromatic hydrocarbons with granular activated carbon

“…However, at high PAH concentration, organic matter may still constitute the main binding phase, because of sorption saturation of the BC surface. In addition, sorption to oil may contribute to the strong linear partitioning [14,41].…”

Polyethylene passive samplers to determine sediment–pore water distribution coefficients of persistent organic pollutants in five heavily contaminated dredged sediments

“…Indeed, sorption to BC, such as diesel soot, coal soot, wood charcoal, or char-like carbonaceous particles, renders obsolete the traditional equilibrium partitioning theory (EPT) model assuming linear partitioning to amorphous organic matter (Bucheli and Gustafsson, 2000;Huang et al, 2003;Cornelissen et al, 2004;Cornelissen et al, 2005). Furthermore, a very high sorption capacity, similar or even higher than that of BC, has been previously reported for weathered mineral oil residues for polycyclic aromatic hydrocarbons (PAHs) (Jonker et al, 2003;Brändli et al, 2008) and polychlorinated biphenyls (PCBs) (Cornelissen et al, 2005;McNamara et al, 2005;Jonker and Barendregt, 2006). The sedimentary organic matter heterogeneity, especially the presence of BC and/or oil fractions, thus significantly affects HOC bioavailability and the risks to the environment (Huang et al, 2003;Cornelissen et al, 2005).…”