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 f{sub}(OC)K{sub}(OC) 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 K{sub}(BC)= 6.1 ±0.04) and a Freundlich exponent (n ≈ 0.6 if log K{sub}(OC) = 4.0) that is strongly dependent on the K{sub}(OC) value selected.
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