Spilled Oils: Static Mixtures or Dynamic Weathering and Bioavailability?

Area of Science:

• Environmental Chemistry
• Marine Biology
• Ecotoxicology

Background:

• The MV Selendang Ayu oil spill occurred along Unalaska Island, Alaska.
• Assessing the long-term bioavailability and environmental fate of spilled oil components is crucial for understanding ecosystem impacts.

Purpose of the Study:

• To determine if polynuclear aromatic hydrocarbons (PAHs) from sequestered oil were biologically available 3.6 years post-spill.
• To investigate the weathering mechanisms and transfer of oil constituents to marine organisms and the environment.

Main Methods:

• Analysis of alkane and PAH composition in sequestered oil over time.
• Deployment of passive samplers and collection of indigenous mussels for PAH analysis.
• Comparison of PAH concentrations and compositions between oiled and non-oiled reference areas.

Main Results:

• Weathering significantly altered the composition of spilled oil, with smaller PAH molecules being preferentially lost.
• PAHs lost from weathered oil were detected in mussels and passive samplers deployed in July 2008.
• PAH concentrations and patterns in mussels and samplers differed significantly from the reference area, indicating uptake from the spilled oil.
• Hydrocarbons were transferred from sequestered oil to mussels and passive samplers, suggesting aqueous transfer.

Conclusions:

• Thermodynamically driven weathering is a probable mechanism for organism exposure to PAHs.
• Dissolved hydrocarbons from weathered oil remain detectable in the environment and can be taken up by marine organisms.
• Despite low concentrations, sensitive bioaccumulation and passive sampling methods confirmed the detectability of mobile oil constituents.