Assessing weathered Endicott oil biodegradation in brackish water

We evaluated the biodegradability of physically (WAF) and chemically (CEWAF) dispersed oil in brackish water (salinity ∼6.5 g/L), and the influence of nutrient availability (low nutrient-LN: background water vs. high nutrient-HN: addition of 100 mg NO3-N/L and 10 mg PO4-P/L to background water) on oil biodegradation rates at 15 ± 0.5 °C for 42 days. No oil removal occurred in WAF compared with CEWAF: 24% in HN and 14% in LN within two weeks. The oil biodegradation concerned mainly alkanes as confirmed by GC/MS analyses. Higher O2 consumption (10.30 mg L−1 day−1) and CO2 production (3.89 mg C L−1 day−1) were measured in HN compared with LN (O2: 2.79 mg L−1 day−1, CO2:0.18 mg C L−1 day−1). Estimated biomass of hydrocarbon degraders and heterotrophic bacteria was at least an order of magnitude larger in HN than in LN. Combining dispersants with nutrients could enhance oil biodegradation and help improve oil spill mitigation responses.