Deciphering microbial carbon substrates in PAH contaminated sediments using phospholipid fatty acids, and compound specific delta super(13)C and Delta super(14)C

Stable and radiogenic carbon isotopes ( delta super(13)C and Delta super(14)C) of organic compounds and phospholipid fatty acids (PLFAs), as well as polycyclic aromatic hydrocarbon (PAH) ratios were used to determine sources and fates of organic contaminants in highly contaminated, and less contaminated sediments of Hamilton Harbour. The highly contaminated sediments had an order of magnitude more total petroleum hydrocarbons (TPHs) compared to the less contaminated sediments. The TPHs extracted from both sites were depleted in super(14)C (average Delta super(14)C of -775ppt and -973ppt, for Sites 1 and 2, respectively) consistent with inputs of fossil derived contaminants. Fossil carbon also contributed to the unextractable residue ( Delta super(14)C = -503 plus or minus 55ppt) in the sediment at the highly contaminated site relative to the less contaminated site ( Delta super(14)C = -132 plus or minus 2ppt) indicating inputs of fossil carbon not derived from petroleum or PAHs. Diagnostic PAH ratios (e.g. PAH:NaP between 0.01 and 1), and less negative delta super(13)C (-25.6 plus or minus 0.2ppt) of the unextractable residue indicated that a coal derived source was the most likely source of these inputs. Despite the presence of this fossil carbon, there was little evidence of utilization of ancient carbon by the microbial community. The Delta super(14)C of PLFAs from the highly contaminated site were slightly more super(14)C depleted ( Delta super(14)C = -138 plus or minus 20ppt) relative to the PLFAs from the less contaminated site ( Delta super(14)C = -77 plus or minus 42ppt), demonstrating some microbial metabolism of older carbon; however, the majority of the carbon metabolized was modern at both sites, indicating that there was minimal natural attenuation via bioremediation of fossil fuel organic contaminants.