| Assessing environmental sorption of hydrophobic organic compounds in complicated sediment systems is still difficult, despite the growing attention to the role of black carbon in sorption of hydrophobic organic compounds in sediment matrices. In spite of continuous improvement in methods isolating and quantifying black carbon (BC) in sediments or soils, there are still serious problems with these methods. The challenges can be attributed to several factors, such as complexity of sediments, heterogeneity of black carbon, diverse origins of black carbon, and lack of standardization in definition, identification, and analytical techniques for black carbon.; The objectives of this work were three-fold. Firstly, it was to characterize the sorbents included in the development of a model system, including two types of black carbon (black carbon reference material and standard reference material 2975), Lake Hartwell sediment, and humic substance (Elliot soil humic acid) by diverse chemical and physical analysis. Linking particular chemical or physical characteristics of the various sorbents with sorption behavior of PCB congeners may improve predictive power as well as provide insight to the potential mechanisms for the observed affinities of PCB congeners to the sorbents. Secondly, it was to compare two model black carbon (BC) sorbents that are well characterized employing planar and nonplanar sorbates with similar hydrophobicity [i.e., planar tri-CB (34-3, IUPAC #35) and nonplanar tetra-CB (26-26, IUPAC #54)]. Furthermore, these were compared to Lake Hartwell sediment sorbent (i.e., a natural sorbent with little to no BC). Lastly, it was to develop model sorbent systems to investigate the role of BC and avoid the operational problems with isolation and quantification of BC.; Black carbon and Lake Hartwell sediment were characterized via various instrumental analyses. Both BCRM and SRM 2975 were characterized employing the CHNSO analyzer. The average composition of BCRM determined was 93.122, 1.467, and 3.259 of C%, H%, and O%, respectively. There was no presence of N or S. In the case of SRM 2975, the average composition was obtained as 86.140, 1.193, and 8.800 of C%, H%, and O%, respectively. In contrast to BCRM, N% and S% were determined as 0.475 and 0.746, respectively. The observed values of surface area, total pore volume, and micro pore volume were slightly higher for SRM 2975 compared to BCRM that is, 89.70 (m2/g),{09}0.148 (cm3/g), and 0.0324 (cm3/g), respectively, for SRM 2975{09}in comparison with 70.98 (m2/g), 0.095 (cm 3/g), and 0.0232 (cm3/g), respectively, for BCRM. Solid-state 13C nuclear magnetic resonance (NMR) spectra of BCRM with a cross-polarization/magic angle spinning (CP/MAS), employing spinning rates of 7 KHz and 5 KHz shared only one peak at the chemical shift of 129.6 ppm. For the BCRM sorbent, of the two PCB congeners with similar hydrophobicity, the tri-CB with planar configuration showed distinctively greater sorptivity than the nonplanar tetra-CB. In addition, nF, BC values of 0.336 for the planar tri-CB and 0.440 for the nonplanar tetra-CB were obtained for the BCRM black carbon sorbent.; For developing model sorbent systems, a single sorbate, which was planar, was used (tri-CB). Black carbon (BCRM or SRM 2975) or Elliott soil humic acid was added to the Lake Hartwell sediment suspension as weight based on the LH sediment mass, that is, 0%, 1%, 2%, 4%, and 8%. Equilibration times of 3-4 months were used. The addition of black carbon (SRM 2975 or BCRM) to Lake Hartwell sediment suspension resulted in an obvious enhancement of sorptivity for the planar tri-CB and the enhancement increased with increasing weight % of the amendment. Results of the modeling to predict what has been observed with the amended Lake Hartwell systems indicate that the Kd can be successfully predicted based on the Kd of single sorbents.; The chemical or physical characteristics of a geosorbent such as chemical composition, functi... |
