Polycyclic aromatic hydrocarbon (PAH) source, sediment deposition patterns, and particle geochemistry as factors influencing PAH distribution coefficients in sediments of the Elizabeth River, VA, USA

Sediments and pore waters from two sites in the urbanized Elizabeth River, Virginia were sampled for levels of polycyclic aromatic hydrocarbons (PAHs). Pore water PAH concentrations were similar between Sites 1 and 2, despite sediment PAH concentrations being much greater at Site 2. Organic carbon-normalized distribution coefficients (KOC)obs for all PAHs were significantly higher at Site 2 compared to Site 1, but varied 2–3 orders of magnitude between the top and bottom of the core in the sediments at Site 1. PAH distribution between sediments and pore waters at Site 1 were most notably related to the bimodal sediment deposition patterns as depicted by X-radiograph depth profiles, and PAH isomer concentration ratios. Sedimentary organic carbon/nitrogen ratios, lignin-phenol concentrations, soot carbon, and particle surface area both before and after organic digestion, were also analyzed in order to assess the role of sediment geochemistry on PAH (KOC)obs. Different factors were determined to control particle surface area at each site, offering insight into explaining observed PAH distribution coefficients. At Site 1, sediment organic matter was inaccessible for digestion and perhaps PAH partitioning as well. Sorption of PAHs to mineral surfaces explains low values for PAH distribution coefficients observed in the deeper sediments in this core. At Site 2, large and invariant (KOC)obs may result from sediments comprised of particles (e.g., woody debris) infused with creosote and coated with organic matter sequestering PAHs within the particle matrix. Our results indicate there is significant heterogeneity in PAH distribution coefficients in estuarine sediments, which may be attributed to sediment deposition patterns, PAH source(s), and sediment geochemistry.