Dual effects of a dispersant and nutrient supplementation on weathered Endicott oil biodegradation in seawater

Abstract

Laboratory-scale experiments were conducted to evaluate the biodegradation of physically (WAF) and chemically dispersed (CEWAF) Endicott oil in seawater (salinity: 29.1‰) from Prince William Sound, Alaska, under low nutrient (LN) (background seawater) and high nutrient (HN) (addition of 100 mg NO3-N/L and 10 mg PO4-P/L to background seawater) at 15 ± 0.5 °C for 42 days. The dispersant was Corexit 9500. The dispersed oil concentration of the WAF (0.019 g/L ± 0.002) was an order of magnitude lower than that in the CEWAF (0.363 g/L ± 0.038). While remaining negligible in the WAF, the total oil removal in the CEWAF was 26% and 44% in LN and HN treatments, respectively. Nutrient supplementation significantly accelerated the rate of oil biodegradation as confirmed by ANOVA coupled with Tukey’s test at 95% confidence intervals (α = 0.05). GC/MS analyses revealed that biodegradation affected mainly alkane compounds. In the CEWAF, O2 consumption, CO2 production and biomass were much larger in HN than in LN treatments, which suggests that chemical dispersion of oil coupled with high nutrient concentration could be very useful in terms of remediation strategies and effective responses to oil spill at sea.