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

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 adsorbenttogether can (1) account for sediment--pore-waterdistribution coefficients observed in the field that are greater than predicted by a simple f(OC)K(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(BC) = 6.1 i 0.04) and a Freundlich exponent (n approximately 0.6 if log K(OC) = 4.0) that is strongly dependent on the K(OC) value selected.