Environmental stability of selected petroleum hydrocarbon source and weathering ratios

Weathering and biodegradation alter the composition of spilled oil, making it difficult to identify the source of the release and to monitor its fate in the environment. Using intertidal sediment and terrestrial soil data that cover a wide range of oil weathering states, we show that ratios of alkylated dibenzothiophenes and phenanthrenes are useful for source identification even up to 98% depletion of total polycyclic aromatic hydrocarbons (PAHs). Furthermore, we find that some ratios of alkylated naphthalenes, phenanthrenes, and chrysenes can qualitatively assess the extent of weathering an oil has undergone since a spill. These source and weathering ratios appear to successfully describe oil depletion and to identify sources in subtidal sediment data from the M/C Haven spill in Italy, the Exxon Valdez spill in Alaska, and a North Sea oil spill.