Characterization of organic matter in pristine and contaminated coastal marine sediments using solid-state C-13 NMR, pyrolytic and thermochemolytic methods: A case study in the San Diego harbor area

Chemical composition of coastal marine sedimentary organic matter (SDOM) is a function of natural and anthropogenic inputs to the system. In this stud y a combination of analytical techniques: C-13 nuclear magnetic resonance ( NMR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and tetrame thylammonium hydroxide thermochemolysis-gas chromatography/mass spectrometr y (TMAH thermochemolysis-GC/MS) were used to study the contribution of hydr ophobic organic contaminants and terrestrial OM to the SDOM- Sediments were collected from two sites in the San Diego Bay: Paleta Creek, which is cont aminated, and Coronado Cayes, which is relatively pristine. Concentrations of polycyclic aromatic hydrocarbons (PAHs) at both sites, as determined by ultrasonically assisted lipid extraction are found to be higher in the surf ace layer, to generally decrease with depth,, and to be present at about tw o orders of magnitude higher concentration at the contaminated site as comp ared to the pristine site, The sediment samples were partially deashed with HF/HCl treatment before further analysis. C-13-NMR spectra of the Paleta C reek samples show a higher aromatic carbon content and a distinct phenolic carbon peak. This suggests a large input from terrestrial carbon (lignin). Data from both Py-GC/MS and TMAH thermochemolysis-GC/MS support this and in dicate the presence of lignin-derived residues, primarily of the guaiacyl t ype at the contaminated site. In contrast, SDOM at the Coronado Cayes site exhibits less terrestrial input. In general, the SDOM resembles soil OM rat her than typical marine SDOM- Chemical analyses of the lipid-extracted, par tially deashed sediments, does not reveal the presence of any PAHs. (C) 200 1 Elsevier Science Ltd. All rights reserved.