Cooperative Sorption of Organic Chemicals in Systems Composed of Low Organic Carbon Aquifer Materials

The effect of a nonionic, low-polarity cosolute (tetrachloroethene) on the sorption of three nonionic, low-polarity organic chemicals (naphthalene, p-xylene, 1,4-dichlorobenzene) by two aquifer materials with low organic carbon contents (<0.03 %) was investigated. The results of miscible-displacement experiments performed with single- and binary-solute solutions were compared to elucidate the occurrence of antgonistic or synergistic interactions. In all cases, the sorption of the primary solute was enhanced by the presence of tetrachloroethene. Equilibrium sorption constants measured in binary-solute systems were 1.5-3 times larger than those measured for the single-solute systems. Hence, tetrachloroethene had a synergistic (i.e., cooperative), rather than an antagonistic (i.e., competitive), effect on the sorption of the primary solutes. The enhanced sorption was postulated to result from sorbed tetrachloroethene increasing the effective organic carbon content of the sorbent.