Reinterpreting Literature Sorption Data Considering both Absorption into Organic Carbon and Adsorption onto Black Carbon

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Abstract
We hypothesized that the sorption of polycyclic aromatic hydrocarbons (PAHs) to natural sediments and soils should consider both absorption into a biogenic/diagenetic organic carbon (OC) fraction and adsorption onto a combustion-derived, black carbon (BC) fraction. Here, two sets of literature data were reevaluated to illustrate that an OC absorbent and a BC adsorbent together can (1) account for sediment−pore-water distribution coefficients observed in the field that are greater than predicted by a simple focKoc partitioning model and (2) explain a group of nonlinear phenanthrene isotherms observed in the laboratory with a single value for the BC-normalized distribution coefficient (log KBC = 6.1 ± 0.04) and a Freundlich exponent (n ≈ 0.6 if log Koc = 4.0) that is strongly dependent on the Koc value selected.