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Biodegradability Of Lingering EVOS Oil 19 Years After The Spill (Presentation)
Citation:
VENOSA, A. D., P. Campo, AND M. T. Suidan. Biodegradability Of Lingering EVOS Oil 19 Years After The Spill (Presentation). Presented at International Oil Spill Conference (IOSC) 2011, Portland, OR, May 23 - 26, 2011.
Impact/Purpose:
To measure the biodegradability and biodegradation rate of the weathered 19-year lingering oil in laboratory microcosms and determine if the lingering oil was still biodegradable enough in regards to the rate of biodegradation to warrant recommending a full-scale bioremediation effort.
Description:
In 2001 and 2003, NOAA scientists conducted geospatial surveys of lingering oil in Prince William Sound (PWS) and concluded areas were still contaminated with substantial subsurface oil from the 1989 Exxon Vladez oil spill (EVOS). In 2007, a mass weathering index (MWI) was developed by Exxon-Mobil consultants based on the degree of weathering of PAHs normalized to conserved biomarkers, suggesting that if the degree of weathering of oil is 70% or more, further attempts at bioremediation would be unjustified. The objective of our study was to measure the biodegradability and biodegradation rate of the 19-year lingering oil under conditions where nutrients and oxygen are not limiting. Samples of beach substrate were collected in the summer of 2008 from representative sites in PWS contaminated with oil residues of varying weathering states according to the MWI model. Enough sacrificial microcosms were set up to accommodate two treatments for each site (natural attenuation and biostimulation). Results indicated that lingering oil is still biodegradable. Nutrient addition significantly stimulated biodegradation (p < 0.01) compared to natural attenuation in all treatments regardless of the degree of weathering. Non-linear regression analyses were conducted to calculate first-order biodegradation rate coefficients. The most biodegradable oil was the one most weathered according to the MWI. A surprising finding was that substantial biodegradation occurred in the natural attenuation microcosms due to the high Total Kjeldahl Nitrogen (TKN) content of the sediments. Most of the observed biodegradation in all microcosms was due to the presence of dissolved oxygen, absent in the field because of sequestration of the oil in low permeability sediment layers. Nitrogen was also a limiting factor but was overshadowed by oxygen. FOR FURTHER INFORMATION, CONTACT ROGER B. YEARDLEY, JR., LAND REMEDIATION AND POLLUTION CONTROL DIVISION, AT 513-569-7548.