The effect of pore water chemistry on the biodegradation of the Exxon Valdez oil spill

摘要

Knowledge of the oxygen and nutrient concentrations in an oil-contaminated Prince William Sound (PWS) beach is important for understanding of the oil persistence over two decades after the Exxon Valdez spill. It was traditionally believed that there was enough oxygen in the contaminated shorelines to sustain aerobic microbial metabolism of oil and that nutrients were the major factors limiting oil biodegradation. In the present study, we analyzed the oxygen and nutrients levels in both clean and oily areas on a PWS beach that was heavily contaminated by the Exxon Valdez oil spill. We found that the level of nitrogen and phosphorous were 0.454 mg-NL~(-1) and 0.033 mg-PL~(-1), respectively, which is not sufficient to fully support microbial growth, confirming that nutrient concentration was a major factor limiting oil transformation by biological ways. We also observed that the oxygen level varied from higher than 3 mgL~(-1) in the clean wells to about 1 mgL ~(-1) (near anoxic level) in the oily wells. In addition, the lowest nitrate levels were observed at the oily wells. Altogether, these results suggest that the low level of efficient electron acceptors (oxygen and nitrate) detected at the oily spot is responsible for slow and potentially inefficient biodegradation of the oil.