Sorption of polycyclic aromatic hydrocarbons to lampblack and polyoxymethylene

Lampblack is a residue found at former oil-gas manufacturing sites at which crude oil was decomposed at high temperatures. Lampblack may be coated or impregnated with oil gasification by-products, among which polycyclic aromatic hydrocarbons (PAHs) are the compounds of the greatest regulatory concern. This study investigated the sorption mechanism of PAHs in lampblack and lampblack-impacted field soils and assessed PAH availability to the aqueous environment. Lampblack-impacted field soil samples were obtained from five sites in California that formerly housed oil-gas process operations. PAH analyses on both whole samples and density-separated components demonstrated that 81-100% of PAHs in the lampblack-impacted soils were associated with lampblack particles. FTIR, 13C NMR, and SEM analyses showed that oil-gas lampblack solids comprise primarily aromatic carbon with soot-like structures. Long-term aqueous equilibrium experiments with both field and laboratory-prepared lampblack samples showed that lampblack has a very strong affinity for PAHs, which results in greatly reduced availability of PAHs to the aqueous phase. However, an oil tar phase present in the lampblack matrix could significantly influence sorption of PAHs to lampblack by competing for sorption sites on the lampblack surface.; In order to facilitate the examination of PAH sorption behavior in lampblack and lampblack-impacted soils, a passive sampling technique using a polyoxymethylene (POM) partitioning method was evaluated for applications in environmental analytical measurement of the aqueous availability of hydrophobic organic compounds from soils and sediments. The sorption behavior of 12 PAH compounds to POM were examined over a wide range of aqueous equilibrium concentrations. Uptake kinetic studies of PAHs into POM were performed in batch systems with different volume ratios of POM-to-aqueous phase. Coupled diffusion and mass transfer models were used to describe the uptake of PAHs into POM and to assess the physicochemical properties and experimental conditions that controlled uptake rates. The POM partitioning technique is demonstrated to compare favorably with two other procedures (air bridge and alum flocculation) for measuring PAH soil-water distribution coefficients with lampblack-impacted soils.