EFFECTS OF SALINITY CHANGES AND THE FORMATION OF DISSOLVED ORGANIC-MATTER COATINGS ON THE SORPTION OF PHENANTHRENE - IMPLICATIONS FOR POLLUTANT TRAPPING IN ESTUARIES

Estuaries have been reported to be sinks far hydrophobic pollutants, a nd sorption has been commonly attributed to be an important mechanism responsible for the observed pollutant trapping. The sorption enhancem ent caused by ''salt effects'' and dissolved organic matter (DOM) coat ings were both measured and modeled, and the results were used to prob e the extent to which equilibrium sorption could explain estuarine pol lutant trapping. The polycyclic aromatic compound phenanthrene, an ext racellular polymer from a soil bacterial isolate, and a low organic ca rbon kaolinite were used as models for the hydrophobic pollutant, DOM, and suspended sediment, respectively. Sorptive interactions between p henanthrene, extracellular polymer, and kaolinite were measured at pH 8 as a function of salinity. The experimentally determined binary dist ribution coefficients were combined using a three-component sorption m odel to calculate the overall sorption coefficient for phenanthrene, K -0. Increasing the ionic strength to seawater levels increased the ove rall sorption coefficient by 55% as compared to the freshwater Value w hile the presence of polymer coatings increased K-0 by 9% at all salin ities. The three-component model simulation of sorption in the estuary showed that only 0.1% of available phenanthrene would be sorbed to su spended sediment given reasonable estimates of the DOM and particulate concentrations. Order of magnitude analyses carried out with other co mbinations of estuarine DOM and sediments also fell short of levels re quired to explain observed estuarine pollutant trapping. These experim ents and model simulations lead to the conclusion that equilibrium sor ption of phenanthrene cannot explain the full extent of pollutant trap ping in estuaries.