PAH Sorption Mechanism and Partitioning Behavior in Lampblack-Impacted Soils from Former Oil-Gas Plant Sites

Abstract

This study assessed polycyclic aromatic hydrocarbon (PAH) association and aqueous partitioning in lampblack-impacted field soils from five sites in California that formerly housed oil-gas process operations. Lampblack is the solid residue resulting from the decomposition of crude oil at high temperatures in the gas-making operation and is coated or impregnated with oil gasification byproducts, among which PAHs are the compounds of the greatest regulatory concern. A suite of complementary measurements investigated the character of lampblack particles and PAH location and the associated effects on PAH partitioning between lampblack and water. PAH analyses on both whole samples and density-separated components demonstrated that 81-100% of PAHs in the lampblack-impacted soils was associated with lampblack particles. FTIR, 13C NMR, and SEM analyses showed that oil-gas lampblack solids comprise primarily aromatic carbon with soot-like structures. A free-phase aromatic oil may be present in some of the lampblack soils containing high PAH concentrations. Comparable long-term aqueous partitioning measurements were obtained with an air-bridge technique and with a centrifugation/alum flocculation procedure. Large solid/water partition coefficient (Kd) values were observed in samples exhibiting lower PAH and oil levels, whereas smaller Kd values were measured in lampblack samples containing high PAH levels. The former result is in agreement with an oil-soot partitioning model, and the latter is in agreement with a coal tar-water partitioning model. Lampblack containing high PAH levels appears to exhaust the sorption capacity of the soot-carbon, creating a free aromatic oil phase that exhibits partitioning behavior similar to PAHs in coal tar. This study improves mechanistic understanding of PAH sorption on aged lampblack residuals at former oil-gas sites and provides a framework for mechanistic assessment of PAH leaching potential and risk from such site materials.

The Determination of Sediment Polycyclic Aromatic Hydrocarbon (PAH) Bioavailability using Direct Pore Water Analysis by Solid-Phase Microextraction (SPME)

“…However, in the presence of a free oil phase, the black carbon particles are inactivated and behave no different from wood particles as evidenced by similar PAH concentrations on wood and coal particles in this sediment. The interpretation of the role of black carbon on PAH partitioning in sediment needs to be interpreted carefully when there is free oil phase present as discussed in detail by Hong et al (2003). In summary, the toxicity of sediment PAHs to H. azteca in this sample is a function of the free oil phase coating which negates the effect of SOC on sequestering PAHs.…”

“…Thus, interpretation of the role of black carbon on PAH partitioning in sediment needs to be interpreted carefully when there is free oil phase present as discussed in detail by Hong et al (2003).…”

Characterization of Contaminant Migration Potential Through In-Place Sediment Caps

“…(Peters, C., et al, 1999). This system more adequately describes the sediment found at many PAH contaminated sites with high concentrations of free phase creosote or coal tar (Hong L. et al, 2003). The modeling utilizes ordinary differential equations describing the mass balances in the creosote and water phases of the modeled porous media.…”

Resuspension of polychlorinated biphenyl‐contaminated field sediment: release to the water column and determination of site‐specific KDOC

“…To the no alum treatment, no further work was performed. To the alum alone and alum with centrifugation treatments, alum was added (1.25 mM final concentration) following methods from Ghosh et al [25] and Hong et al [26]. To both alum treatments, 1 M NaOH was added dropwise to bring the pH to neutral.…”

“…For these reasons, alum was chosen as the method of DOC removal. We began by adding 1.25 mM alum, a concentration used previously by others conducting similar experiments [25,26]. Alum significantly reduced DOC concentrations in resuspension supernatant and PCB mass uptake into PE samplers (Supplemental Data, Table S1).…”