Sorption and biodegradation of ionizable polycyclic aromatic hydrocarbons (IPAHs) in estuarine sediment

In the first part of this research, adsorption of quinoline (pK a = 4.92) and background electrolyte (CaCl2) onto specimen kaolinite and montmorillonite were measured as a function of pH (3-7.5) and ionic strength (1-10 mM), and as a function of quinoline concentration (0.02-1.55 mM) at fixed pH values of maximum adsorption. Maximum sorption of quinoline occurred at pH 3.5-4.0 for kaolinite, and pH 3.0-5.0 for montmorillonite. At their respective pH values of maximum adsorption, the sorption capacity for quinoline was 100 times greater with montmorillonite than kaolinite on mass basis. Selectivity coefficients, which were calculated from pH edge data, indicated selectivity for cationic quinoline (QH+) over Ca 2+ was greater with montmorillonite (Kexc = 27 at pH 4) compared to kaolinite (Kexc = 1.6 at pH 4), and Kexc was not affected by ionic strength for either clay. The results indicate the important role of charged siloxane sites in the adsorption of this N-heterocyclic contaminant.; In the second part of this research, sorption and biodegradation of structurally similar compounds of ionizable polycyclic aromatic hydrocarbons (IPAHs) in an estuarine sediment were studied. The sorption of 16 IPAHs to the sediment was measured in synthetic estuarine water as a function of IPAH concentration (1-100 muM) at fixed ionic strength (0.4 M), pH (7.6+/-0.2), and sediment concentration (0.371 g C kg-1 suspension) after a 24 h equilibration period.; Biodegradation experiments with 20 IPAHs (naphthalene-based and quinoline-based structures) were initially conducted with two pure cultures in order to select the most metabolically capable organism. The two cultures included Neptunomonas naphthovorans (ATCC 700638), isolated from PAH-contaminated sediment in Puget Sound, WA, and unidentified NP-1, isolated from municipal wastewater in State College, PA. The initial "screening" experiments revealed that N. naphthovorans could biodegrade 11 of the 20 IPAHs, while NP-1 could biodegrade 9 of the 20 IPAHs. Therefore, all further experiments were conducted with N. naphthovorans. Experiments were conducted in synthetic estuarine water in the absence and presence of estuarine sediment (0.371 g C kg-1 suspension) at a constant initial IPAH concentration of 32 muM, at fixed ionic strength (0.4 M) and pH (7.6+/-0.2). Biodegradation kinetics for all 11 IPAHs were not universally well fit to a simple reaction-order model (e.g., zero-order or first-order), therefore, the percent final extent of biodegradation after 5 days (%FE; where high %FE corresponds to greater degradation) was used to compare biodegradability among the IPAHs, and to develop predictive QSARs. The predictive QSARs showed that log %FE of IPAHs (naphthalene-based structure) exhibited poor positive correlations with log Sw and log Kow, negative correlation with pKa1 ; and no correlation with 1chi. The presence of sediment resulted in reduced final extent of 3-hydroxy-7-methyl-2-naphthoic acid, 4-fluoro-2-naphthoic acid, quinoline, and quinoxaline but no effects on the final extent of 1-hydroxy-2-naphthoic acid, 1,8-naphthaldehydic acid, and 6-amino-2-naphthoic acid. A log K oc' -log %FE (naphthalene-based structure) showed positive correlation. (Abstract shortened by UMI.)...