Evaluating competitive sorption mechanisms of volatile organic compounds in soils and sediments using polymers and zeolites.

The competitive sorption of trichloroethene (TCE) and tetrachloroethene (PCE) was investigated in three natural solids, two polymers, and four zeolites. Competition was observed in natural solids with high contents of recalcitrant organic carbon, in the glassy polymer, and in zeolites with strongly and moderately hydrophobic micropores of large (7.5 x 10 A) and small pore widths (approximately 5.4 A), respectively. Isotherm results and recalcitrant OC% values for natural solids indicate that the extent of competition between TCE and PCE is related to the amount of hard organic carbon. Gas adsorption results and the variability in C/H values suggest that natural organic matter contains micropores with varying width and polarity. Isotherm results for zeolites indicate that competition between TCE and PCE increases with increasing hydrophobicity and decreasing micropore width. We suggest that competition between volatile organic contaminants in the subsurface is controlled by competition for hydrophobic micropores in hard organic matter and that smaller more hydrophobic micropores result in stronger competition.