Depth-related influences on biodegradation rates of phenanthrene in polluted marine sediments of Puget Sound, WA.

Abstract: A whole-core injection method was used to determine depth-related rates of microbial mineralization of ¹⁴C-phenanthrene added to both contaminated and clean marine sediments of Puget Sound, WA. For 26-day incubations under micro-aerobic conditions, conversions of ¹⁴C-phenanthrene to ¹⁴CO₂ in heavily PAH-contaminated sediments from two sites in Eagle Harbor were much higher (up to 30%) than those in clean sediments from nearby Blakely Harbor (<3%). The averaged ¹⁴C-phenanthrene degradation rates in the surface sediment horizons (0–3cm) were more rapid (2–3 times) than in the deeper sediment horizons examined (>6cm), especially in the most PAH polluted EH9 site. Differences in mineralization were associated with properties of the sediments as a function of sediment depth, including grain-size distribution, PAH concentration, total organic matter and total bacterial abundance. When strictly anaerobic incubations (in N₂/H₂/CO₂ atmosphere) were used, the phenanthrene biodegradation rates at all sediment depths were two times slower than under micro-aerobic conditions, with methanogenesis observed after 24 days. The main rate-limiting factor for phenanthrene degradation under anaerobic conditions appeared to be the availability of suitable electron acceptors. Addition of calcium sulfate enhanced the first order rate coefficient (k ₁ increased from 0.003 to 0.006day⁻¹), whereas addition of soluble nitrate, even at very low concentration (<0.5mM), inhibited mineralization. Long-term storage of heavily polluted Eagle Harbor sediment as intact cores under micro-aerobic conditions also appeared to enhance anaerobic biodegradation rates (k ₁ up to 0.11day⁻¹). [Copyright &y& Elsevier]