Natural Weathering of Petroleum and the Applicability of Bioremediation for Oil Spill Cleanup: The Exxon Valdez Experience Ronald Atlas University of Louisville James R. Bragg Creative Petroleum Solutions LLC
Biodegradation is an Important Process that Removes Oil from the Marine Environment • “Natural biodegradation is ultimately one of the most important means by which oil is removed from the marine environment, especially the nonvolatile components of crude or refined petroleum.” • “… with enough time, microorganisms can eliminate many components of oil from the environment.” U.S. Congress, Office of Technology Assessment, Bioremediation for Marine Oil Spills—Background Paper, OTA-BP-O-70 (Washington, DC: U.S. Government Printing Office, May 1991)
Diverse Marine Microorganisms Utilize Various Hydrocarbon Biodegradation Pathways to Degrade the Compounds in Crude Oil CH 3 n -Alkane COOH Alcohol + H 2 O OH COOH Aldehyde OH OH COOH NH 2 OH OH Catechol Fatty acid CH 3 O TCA CO 2 Ring fission R-CH 2 -CH 2 -C-SCoA FAD Fatty acyl CoA COOH FADH 2 O COOH Acetyl CoA OH R-C-SCoA O O R-CH CH-C-SCoA HOOC OH C -C-SCoA Protocatechuate H 3 H 2 O CH 3 OH CoASH COOH OH O O O R-C-CH 2 -C-SCoA R-CH -CH 2 -C-SCoA COOH HO OH COOH OH OH OCH 3 H++ NADH + + OH NAD OH
Oil Spill Bioremediation Enhances Rates of Biodegradation ( Does not change extent of degradation) Carbon dioxide + Water Microbe Salinity Hydrocarbons Microbe Microbe Microbe Temperature Polars Fertilizer
Key Factors Affecting Whether the Rate of Oil Biodegradation Can be Accelerated Sufficiently by Nutrient Addition to Justify Bioremediation Concentrations of naturally available nutrients must be limiting the biodegradation rate Sufficient oxygen must be present For shorelines, oil residues must have sufficient contact with flowing water to supply necessary nutrients and oxygen Benefits must outweigh risk that oil will cause ecological harm—efficacy and safety must be demonstrated
Demonstrating Efficacy of Bioremediation Laboratory Studies and Field Demonstrations
Assessing Oil Weathering & Biodegradation Mass ratio method % loss of component X = [1- (C x /C con ) w (C x /C con ) s ] x 100 Where: C x = Mass concentration of component X in oil C con = Mass concentration of conserved species in oil (e.g., hopane or stigmastane) w = weathered sample s = source or reference sample
Sequence of Hydrocarbon Biodegradation • Alkanes Degraded Most Rapidly • Aromatics are also Degraded. • Polars are Generally Recalcitrant
Exxon Valdez PAH Weathering Sequence Increasing weathering; compositional changes with time; and loss of total polynuclear aromatics
Rates of Biodegradation of PAHs were Dependent on Number of Rings in Field Test at KN135
Depletion of Alkylated Phenanthrenes Follows Expected Biodegradation Trends from PWS Samples Collected from 2001-2008 100 C1-Phenanthrene % Depletiion of Alkylated C2-Phenanthrene 80 C3-Phenanthrene C4-Phenanthrene Phenanthrene 60 40 20 0 0 20 40 60 80 100 % Depletion Total PAH
The PAH Content Decreases due to Various Weathering Processes Including Biodegradation
Dispersants Increase Rate of Biodegradation by Increasing Oil/Water Interfacial Area Increasing Dispersion Dispersants Biodegradation Extent of Control Time (days)
Bioremediation of Exxon Valdez Spill: Addition of Nitrogen Fertilizers Accelerated Rates of Hydrocarbon Biodegradation by Indigenous Bacteria
Fertilizer Addition Enhanced Rates of Biodegradation in Field Tests without Causing Toxicity to Fish or Eutrophication and Algal Blooms
Extent of Rate Enhancement was Related to the Ratio of Nitrogen to Biodegradable Oil in PWS Field Tests
Fertilizer Addition was Shown to be Safe Extensive Testing Prior to, and During Field Application of Fertilizer to Ensure Environmental Safety • Prescreening of all fertilizers in laboratory tests with aquatic biota − Upper safe limits for ammonia based on Ambient EPA Water Quality Criteria (9.8 ppm max, 1.5 ppm continuous at shoreline conditions) − Toxicity tests conducted by EPA and Exxon using Inipol fertilizer and various marine biota species • 1990 PWS bioremediation test monitoring – Nearshore water monitored for toxicity to sensitive marine species – Potential for algal growth stimulation measured by chlorophyll concentrations in water – Monitored for oil washout and persistence of 2-butoxyethanol in Inipol liquid fertilizer, including using caged mussels • Full-scale field application monitored • Ammonia at ten locations was well below EPA guidelines
Oxygen Concentrations Decreased in Pore Water Following Fertilizer Application but Not Totally Depleted
Changes in Bacterial Populations
Many Commercial Products were Proposed for use by Exxon: None Had Sufficient Scientific Efficacy Data to Warrant Use Duck Feathers Orange and Oil Eating Bacterial Cultures Lemon Peels
Full Scale Bioremediation Using Fertilizer Addition was Applied Extensively in Prince William Sound From 1989 to 1991
Extent of Fertilizer Application in the Largest Use of Bioremediation Nitrogen Applied Nitrogen Applied in 1989 in 1990
By 2001 NOAA Estimated that 99.6% of the Spilled Oil Was Gone from Prince William Sound -- Microbes and Other Weathering Processes Worked
Only a Few Sites with Subsurface Oil Remained in 2001 Oiled Sediment Volume in 2001 Oiled Sediment Volume in 2001 Estimated by NOAA* (m ) 3 Estimated by NOAA* (m 160 160 3 ) ( HOR HOR MOR MOR 120 120 LOR LOR OF OF 80 80 40 40 0 0 Segment Segment * J. Michel, et al., 2006 * J. Michel, et al., 2006
Overview of Total PAH (TPAH) Depletion for 761 Pit Samples Dug During 2007-2008 Surveys Less than 3% of the 761 total pits examined in 2007-2008 had SSO residue that was less than 70% depleted of TPAH Oil with TPAH Oil with TPAH Oil with TPAH Oil with TPAH Depletion < 70% Depletion < 70% Depletion > 70% Depletion > 70% 2.9% of total pits 2.9% of total pits 13.5% of total pits 13.5% of total pits No oil or No oil or TPAH < 500 ng/g sediment TPAH < 500 ng/g sediment 83.6% of total pits 83.6% of total pits (Background Levels) (Background Levels)
Most of the SSO Found in Pits in 2007-2008 Surveys Was Highly Weathered, Especially Within the Biologically Important Lower Intertidal Zones (0 to 1 M Elevation) 100 % of Pits at Each Elevation With 90 Elevation Total Pits Dug Total PAH Depletion < 70% +3 meter 188 80 +2 meter 191 +1 meter 171 70 0 meter 163 60 50 40 30 20 8% 3% 1% 1% 10 0 3 M 2 M 1 M 0 M Elevation Above Mean Low Tide
Distribution of TPAH depletion in 2007 for SM006B SM006B 67 67 90 90 73 73 94 94 57 57 94 94 88 88 76 76 98 98 82 82 77 77 90 90 83 83 +3 m +3 m 10 m 10 m +2 m +2 m +1 m +1 m +1 m Oil: % TPAH Oil: % TPAH Oil: % TPAH Oil: % TPAH Depletion > 70% Depletion > 70% Depletion < 70% Depletion < 70% 23 % 23 % 5% 5% = No oil (includes pits with TPAH <500 ng/g sed.) No Oil No Oil % = Depletion > 70% 72% 72% = Depletion < 70% % % of Total Pits % of Total Pits (This site contained 44% of all HOR & MOR found by NOAA in 2001)
Distribution of TPAH Depletion for SM005B Workers 64 76 SM005B SM005B = No oil (includes pits Oil: % TPAH Oil: % TPAH Oil: % TPAH Oil: % TPAH Depletion < 70% Depletion < 70% with TPAH Depletion > 70% Depletion > 70% 2% 2% Depletion > 70% 2% 2% <500 ng/g sed.) % = Depletion > 70% No Oil No Oil 96% 96% = Depletion < 70% % % of Total Pits % of Total Pits
Distribution of TPAH Depletion in 2007 for EL056C (Also Showing Site of Trench Dug in 2008) 66 TRENCH Trench 62 Oil: % TPAH Oil: % TPAH Depletion > 70% Depletion < 70% 27% 15% = No oil (includes pits 27% 15% with TPAH 2 <500 ng/g sed.) 7 % = Depletion > 70% % NO OIL = Depletion < 70% No Oil % 58% 58%
Vertical Trench at EL056C Clearly Demonstrates Total PAH Depletion in Sequestration of SSO Residue EL056C Vertical Trench 1500 1500 1500 TPAH = 6000 ng/g sed. TPAH = 6000 ng/g sed. Depth below 1000 1000 1000 Depth below % depletion TPAH = 90.4% % depletion TPAH = 90.4% Surface Cobbles 500 500 500 Surface Cobbles 0 cm 0 cm 0 0 0 PAH Concentration (mg/kg extract) PAH Concentration (mg/kg extract) TPAH = 46800 ng/g sed. TPAH = 46800 ng/g sed. 1500 1500 1500 % depletion TPAH = 78.8% % depletion TPAH = 78.8% 1000 1000 1000 500 500 500 25 cm 25 cm 0 0 0 TPAH = 15200 ng/g sed. TPAH = 15200 ng/g sed. 1500 1500 1500 % depletion TPAH = 55.3% % depletion TPAH = 55.3% 1000 1000 1000 Highly 500 500 500 Upper Oiled Degraded SSO 0 0 0 “fringe” TPAH = 22500 ng/g sed. TPAH = 22500 ng/g sed. 1500 1500 1500 56 cm 56 cm % depletion TPAH = 48.5% % depletion TPAH = 48.5% 1000 1000 1000 500 500 500 Less Oil lens 0 0 0 Degraded SSO TPAH = 165 ng/g sed. TPAH = 165 ng/g sed. 1500 1500 1500 76 cm 76 cm 1000 1000 1000 Lower Oiled “Fringe” No SSO 500 500 500 0 0 0 91 cm 91 cm Pit Bottom Pit Bottom
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