Deciphering microbial carbon substrates in PAH contaminated sediments using phospholipid fatty acids, and compound specific δ13C and Δ14C

Stable and radiogenic carbon isotopes (delta C-13 and Delta C-14) 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 C-14 (average Delta C-14 of -775 parts per thousand and -973 parts per thousand, for Sites 1 and 2, respectively) consistent with inputs of fossil derived contaminants. Fossil carbon also contributed to the unextractable residue (Delta C-14 = -503 +/- 55%) in the sediment at the highly contaminated site relative to the less contaminated site (Delta C-14 = -132 +/- 2 parts per thousand) 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 C-13 (-25.6 +/- 0.2 parts per thousand) 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 C-14 of PLFAs from the highly contaminated site were slightly more C-14 depleted (Delta C-14 = -138 +/- 20 parts per thousand) relative to the PLFAs from the less contaminated site (Delta C-14 = -77 +/- 42%), 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. (C) 2014 Elsevier Ltd. All rights reserved.