The sorption of seven endocrine disrupting chemicals (EDCs) to aquatic colloids was determined by cross-flow ultrafiltration (CFUF) followed by gas chromatography-mass spectrometry (GC-MS). Results show that the colloidal organic carbon normalized sorption coefficient (Kcoc) of EDCs to different aquatic colloids varies by a factor of 6-12 because such colloids are of different origin. Through characterization of colloidal samples, a significant relationship was established between Kcoc values and the molar extinction coefficient of colloids at 280 nm, whereas no other colloidal properties such as elemental ratios were correlated with Kcoc values. The results are consistent with other reports of the importance of the quality of sorbents such as their aromatic carbon content in sorbing various organic pollutants. The presence of a surfactant was found to increase Kcoc values for estrone (El) and 17alpha-ethynylestradiol (EE2). The method was subsequently applied for determining EDC concentrations in field samples, where both conventional and truly dissolved EDCs showed higher concentrations close to sewage outfalls than either upstream or downstream, confirming the sourceconcentration relationship. In addition, the truly dissolved EDC concentrations were lower than the conventional dissolved concentrations, confirming that there were interactions between aquatic colloids and EDCs. It is estimated that between 10 and 29% of EDCs are associated with aquatic colloids. As colloids are highly abundant in rivers and ocean, they will therefore play a significant role in the environmental behavior and fate of EDCs.

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