Citation:

VENOSA, A. D., P. Campo-Moreno, S. Chung, AND M. T. Suidan. Biodegradability Of Lingering Oil 19 Years After The EVOS Spill. Presented at The Tenth International In Situ and On-Site Bioremediation Symposium; A4. Petroleum Hydrocarbons: Biotreatments, Baltimore, MD, May 04 - 08, 2009.

Impact/Purpose:

To measure the biodegradability of the lingering oil in Prince William Sound under conditions where nutrients and oxygen are not limiting.

Description:

In 2001 and 2004, scientists from the National Oceanic and Atmospheric Administration (NOAA) conducted geospatial surveys of lingering oil in Prince William Sound (PWS) and found that about 11 hectares of shoreline remain contaminated with nearly 56,000 kg of subsurface oil from the 1989 Exxon Valdez oil spill (EVOS). Much of the lingering oil was present in subsurface sediments in the middle intertidal zone of the contaminated beaches. Although substantial weathering had occurred, the researchers concluded high concentrations of toxic and mutagenic contaminants were present, suggesting that this lingering oil poses an ongoing threat to organisms that encounter it. In 2007, Atlas and Bragg developed a bioremediation index based on the degree of weathering of oil normalized to conserved biomarkers such as hopanes, stigmastanes, cholestanes, and others. They argued that, if the degree of weathering of oil normalized to one of the conserved biomarkers is 70 % or more, then further attempts to bioremediate it would be futile since the weathering is so extensive that additional effort would not be justified. However, according to the NOAA surveys, the Atlas-Bragg index does not fully account for the PAH content of the lingering oil in PWS. Sufficient PAHs appear to be present in some of the PWS sites to justify further study. The objective of this paper is to measure the biodegradability of the lingering oil in PWS under conditions where nutrients and oxygen are not limiting. Samples of beach substrate were collected by a field crew in the summer of 2008. The samples were collected from representative sites in PWS contaminated with oil residues of varying weathering states in accordance with the Atlas-Bragg model. The three sites were KN114A (Atlas-Bragg index of 76%), SMOO6B (Atlas-Bragg index of 60%), and PWS 3A4 on Eleanor Island (Atlas-Bragg index of 30%). Enough microcosms were set up to accomodate a total of six (6) sacrificial sampling events (corresponding to Days 0, 14, 28, 56, 112, and 168) for seven treatments [natural attenuation (NA) controls and biostimulation treatments for each of the 3 oiled sites and a "positive" control for the PWS 3A4 site]. The NA controls consisted of KN114A, SM006B, and PWS 3A4 microcosms containing seawater but with no nutrient addition. The positive controls consisted of a third series of microcosms from the PWS 3A4 site to which was added crude oil known to be biodegradable (weathered Alaska North Slope crude oil). Substrate for these positive control microcosms consisted of clean, uncontaminated material collected the same way as the other samples. Prior to filling the microcosms in the lab with this material, this sample of substrate was contaminated artificially with the weathered ANS oil at an approximate concentration of 5 g/kg, which is close to the concentration found in many areas containing lingering oil. These microcosms, which were supplied with excess nutrients just like the biostimulation treatment, were sacrificed at the same times as the other treatments above. The source of oil degraders for all microcosms was the collected natural PWS seawater and the beach substrate. Results from the sampling events will be presented and discussed.

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