Essential characteristics of natural dissolved organic matter affecting the sorption of hydrophobic organic contaminants

Association of benzo[a]pyrene (BaP), pyrene, 3,3',4,4'-tetrachlorobiphenyl (TCB) and 2,2',4,4'-tetrabromo diphenyl ether (TBDE) with natural dissolved organic matter (DOM) was studied. The DOM samples were previously collected from natural waters at five Nordic sites during fall 1999 and spring 2000, isolated by the reverse osmosis method, and thoroughly characterized. The purpose was to determine the essential characteristics that predict the sorption capacity of DOM for hydrophobic contaminants. DOM isolates were dissolved in artificial freshwater to give a dissolved organic carbon concentration of 15 mg L-1. Partition coefficients (K-DOC) of the model compounds between water and DOM were measured by the equilibrium dialysis method. Further, the bioavailability of BaP and pyrene to Daphnia magna was tested in the presence of DOM with various qualities. A strong negative correlation was found for the K-DOC values of BaP (R = -0.922) and pyrene (R = -0.929) with spectral absorbency ratio (A(254)/A(400)), while the correlation (R = -0.760) was weaker for the K-DOC values of TCB. The K-DOC values for TCB correlated (R = 0.849) strongly with specific visible absorbency (A(600)/TOC), while the K-DOC values for TBDE correlated (R = -0.739) with relative fluorescence emission. Generally, bioavailability of BaP and pyrene to D. magna reflected the measured association of the compounds with DOM. The data emphasize the importance of aromaticity of DOM, estimated by simple spectroscopic methods, in predicting sorption capacity for polycyclic aromatic hydrocarbons. The situation with halogenated compounds still remains unclear.