Abstract

Experimental measurements demonstrated that rates of in situ microbial anaerobic biodegradation of phenanthrene in undisturbed marine sediments were enhanced when controlled-release electron acceptors (i.e., nitrate and sulfate (for comparison)) were employed. The experimental method used whole and interval cores injected with radiolabeled 14C-phenanthrene, which were incubated, sacrificed, and processed for 14CO2 recovery to determine degradation rates. Nitrocellulose and CaSO4 were formulated to release the electron acceptors into the sediments at rates consistent with bacterial utilization (i.e., that avoided inhibition observed previously at high soluble nitrate (although not sulfate) concentrations). The controlled-release of both compounds, measured in collateral experiments, enhanced the natural anaerobic phenanthrene biodegradation rates by factors up to 2-3. Biodegradation via sulfate reduction was most rapid in the early stages (24 days) of experiments, consistent with reports that many marine bacteria in submerged sediments are sulfate reducers. In comparison, in longer experiments (after 42 days), the anaerobic biodegradation rates were observed at least as high with the addition of nitrocellulose (over 40% of added phenanthrene recovered as 14CO2). Both nitrate and sulfate reduction was observed during anaerobic incubation, although the presence of nitrate seemed to reduce the sulfate reduction. The studied forms of the controlled-release nitrate and sulfate may provide capping amendments to decontaminate marine harbor sediments.