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.

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Bioremediation was used to clean oil-contaminated shorelines in Prince William Sound following the Exxon Valdez oil spill. Among the approaches considered for enhancing natural rates of oil biodegradation, nutrient applications became the principal focus. Bioremediation studies were conducted in a cooperative effort of Exxon, the U.S. Environmental Protection Agency, and scientists in academia. Field testing of nutriation of indigenous oil-eating microorganisms was conducted early in the summer of 1989, and full-scale application followed. Monitoring during the fall and winter of 1989–90 revealed the evident benefit of the technique and supported additional applications in 1990. The efficacy of bioremediation was demonstrated by measurement of numbers of hydrocarbon-degrading microorganisms, microbial hydrocarbon-degrading activities, and chemical changes in residual oil. This paper discusses laboratory and field programs demonstrating the efficacy and environmental safety of bioremediation, and reviews the materials and methods chosen for large-scale application.

Abstract-Current bioremediation techniques for petroleum-contaminated soils are designed to remove contaminants as quickly and efficiently as possible, but not necessarily with postremediation soil biological quality as a primary objective. To test a simple postbioremediation technique, we added earthworms {Eisenia fetidd) or wheat (Triticum aestivum) straw to petroleum land-farm soil and measured biological quality of the soil as responses in plant growth, soil respiration, and oil and grease (O&G) and total petroleum hydrocarbon (TPH) concentrations. Results indicated that plant growth was greater in earthworm-treated land-farm soil. Furthermore, addition of wheat straw resulted in greater total respiration in all soils tested (land-farm soil, noncontaminated reference soil, and a 1:1 mixture of land-farm and reference soils). We observed a 30% increase in soil respiration in straw-amended oily soil, whereas respiration increased by 246% in straw-amended reference soil. Much of the difference between oily and reference soils was attributable to higher basal respiration rates of nonamended oily soil compared to nonamended reference soil. Addition of earthworms resulted in greater total respiration of all soil and straw treatments except two (the land-farm and the 1:1 mixture soil treatments without straw). Straw and earthworm treatments did not affect O&G or TPH concentrations. Nevertheless, our findings that earthworm additions improved plant growth and that straw additions enhanced microbial activity in land-farm soil suggest that these treatments may be compatible with plant-based remediation techniques currently under evaluation in field trials, and could reduce the time required to restore soil ecosystem function.