The sorption of pyrene and anthracene to humic acid-mineral complexes: Effect of fractional organic carbon content

Carbon-normalized distribution coefficients (K-oc) of organic solutes appear to increase as the amount of organic C in a system decreases, This study was conducted to determine the effect of fractional organic C content (f(oc)) on the sorption of anthracene and pyrene, Batch-sorption experiments were conducted on reagent CaCO3, a geologic calcite, and a montmorillonite to measure anthracene and pyrene sorption, An organic C-free mineral surface and two surface loadings of humic acid (HA) were evaluated, The K-oc of anthracene and pyrene varied with f(oc) as well as with the underlying mineral surface, The sorption of anthracene and pyrene to all HA-mineral complexes increased with increases in f(oc) while K-oc for the compounds decreased, In higher f(oc) systems (>3 x 10(-5)), isotherms were C-type curves indicative of partitioning, In lower f(oc) systems (<3 x 10(-5)), isotherms were commonly L and S-type curves indicative of adsorption and condensation, Sources of potential experimental artifact examined were loss of HA from the mineral surface to solution, dissolution of CaCO3 during the experiment, and loss of NOS to experimental glassware or volatilization, None were found to contribute to the observations made, Our results suggest that adsorption-condensation of pyrene and anthracene created more surface excess than predicted by partitioning alone as evidenced by the large experimental K-oc values obtained.