Soot as a Strong Partition Medium for Polycyclic Aromatic Hydrocarbons in Aquatic Systems

Abstract

Abstract. The spatial distributions of polycyclic aromatic hydrocarbons (PAHs) in many aquatic environments appear to be dictated by partitioning with soot as opposed to with bulk organic matter. Recent field-observations of the solid-water distribution coefficients of members of this contaminant assemblage are consistently elevated compared to expectations from organic-matter-based partition models. Increasing hydrophobicity across the PAHassemblage is seen to affect relative distributions. Using PAHs as molecular markers of sorption suggests that an active exchange of such planar molecules between a strong sorbent, such as soot, and the surrounding water is taking place. Quantification of PAHs, organic carbon, and soot carbon in surficial continental shelf sediments off New England revealed that the distribution of PAHs was highly correlated with soot carbon. Estimates of the soot-water partition coefficient for several PAHs, assuming sorbate-soot association is thermodynamically similar to sorbate fusion, are found to agree reasonably well with published aqueous sorption constants to activated carbon.