Natural Weathering of Petroleum and the Applicability of Bioremediation for

Oil Spill Cleanup: The Exxon Valdez Experience

Ronald AtlasUniversity of Louisville

James R. BraggCreative Petroleum Solutions LLC

•

“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)

Biodegradation is an Important Process that Removes Oil from the Marine Environment

OHOH

COOH

C H3

-C-SCoAO

R-CH2-CH2-C-SCoAO

OR-CH CH-C-SCoA

R-CH-CH2-C-SCoAOOH

R-C-CH2-C-SCoAOO

CoASH

R-C-SCoAO

NAD+H++ NADH+

H2 O

FADFADH2

Fatty acyl CoAAcetyl CoA

TCA CO2

n-Alkane

Alcohol + H2 O

Aldehyde

Fatty acid

COOH

CH3

OH

OHOH

Catechol

COOHNH2

OHOHHOOC

CH3

COOH

CH3

OH

COOH

OH

COOH

OHOCH3

COOH

OH

COOH

OHOHHO

Protocatechuate

Ring fission

Diverse Marine Microorganisms Utilize Various Hydrocarbon Biodegradation Pathways to Degrade

the Compounds in Crude Oil

Hydrocarbons Microbe Microbe

Microbe

Microbe

Carbon dioxide + Water

Salinity

Temperature

Fertilizer Polars

Oil Spill BioremediationEnhances Rates of Biodegradation

(Does not change extent of degradation)

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-

(Cx

/Ccon

)w

(Cx

/Ccon

)s ] x 100 Where: Cx

= Mass concentration of component X in oil

Ccon

= Mass concentration of conserved species in oil (e.g., hopane or stigmastane)

w = weathered samples = source or reference

sample

Sequence of Hydrocarbon Biodegradation

•

Alkanes Degraded Most Rapidly

•

Aromatics are also Degraded.

•

Polars are Generally Recalcitrant

Increasing weathering; compositional changes with time; and loss 

of total polynuclear 

aromatics

Exxon Valdez PAH Weathering Sequence

Rates of Biodegradation of PAHs were Dependent on Number of Rings in Field

Test at KN135

0

20

40

60

80

100

0 20 40 60 80 100% Depletion Total PAH

% D

eple

tiion

of A

lkyl

ated

Ph

enan

thre

neC1-PhenanthreneC2-PhenanthreneC3-PhenanthreneC4-Phenanthrene

Depletion of Alkylated Phenanthrenes FollowsExpected Biodegradation Trends from PWS

Samples Collected from 2001-2008

The PAH Content Decreases due to Various Weathering Processes Including Biodegradation

Dispersants Increase Rate of Biodegradation by Increasing Oil/Water

Interfacial Area

Exte

nt o

f B

iode

grad

atio

n

Time (days)

Control

Incr

easi

ng D

ispe

rsio

n

Dispersants

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 SafeExtensive 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 Oil Eating Bacterial CulturesOrange and 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 Appliedin 1990

Nitrogen Appliedin 1989

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

0

40

80

120

160

Segment

HOR

MOR

LOR

OF

Oile

d Se

dim

ent V

olum

e in

200

1Es

timat

ed b

y N

OA

A*

(m3 )

* J. Michel, et al., 2006

0

40

80

120

160

Segment

HOR

MOR

LOR

OF

Oile

d Se

dim

ent V

olum

e in

200

1Es

timat

ed b

y N

OA

A*

(m )3

(

* J. Michel, et al., 2006

Oil with TPAHDepletion > 70%13.5% of total pits

No oil or TPAH < 500 ng/g sediment83.6% of total pits(Background Levels)

Oil with TPAHDepletion < 70%2.9% of total pits

Oil with TPAHDepletion > 70%13.5% of total pits

No oil or TPAH < 500 ng/g sediment83.6% of total pits(Background Levels)

Oil with TPAHDepletion < 70%2.9% of total pits

Overview of Total PAH (TPAH) Depletion for 761Pit 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

0

10

20

30

40

50

60

70

80

90

100

3 M 2 M 1 M 0 MElevation Above Mean Low Tide

Most of the SSO Found in Pits in 2007-2008 Surveys Was Highly Weathered, Especially Within the BiologicallyImportant Lower Intertidal Zones (0 to 1 M Elevation)

% o

f Pits

at E

ach

Elev

atio

n W

ith

Tota

l PA

H D

eple

tion

< 70

% Elevation Total Pits Dug+3 meter 188+2 meter 191+1 meter 171 0 meter 163

8% 3% 1% 1%

= No oil (includes pits with TPAH <500 ng/g sed.)

= Depletion > 70%

= Depletion < 70%%

%

88765794

73 67

98

90

77

83

82

90

10 m +3 m

+2 m+1 m

94

SM006B

88765794

73 67

98

90

77

83

82

90

10 m +3 m+2 m

+1 m+1 m

94

Distribution of TPAH depletion in 2007 for SM006B

Oil: % TPAH Depletion < 70%

5%

Oil: % TPAH Depletion > 70%

23%

No Oil72%

% of Total Pits

Oil: % TPAH Depletion < 70%

5%

Oil: % TPAH Depletion > 70%

23%

No Oil72%

% of Total Pits(This site contained 44% of all HOR & MOR found by NOAA in 2001)

SM005B

Depletion > 70%

SM005B

76

64 Workers

Distribution of TPAH Depletion for SM005B

= No oil (includes pits with TPAH <500 ng/g sed.)

= Depletion > 70%

= Depletion < 70%%

%No Oil96%

Oil: % TPAH Depletion > 70%

2%

Oil: % TPAHDepletion < 70%

2%

% of Total Pits

No Oil96%

Oil: % TPAH Depletion > 70%

2%

Oil: % TPAHDepletion < 70%

2%

% of Total Pits

Trench

No Oil58%

Oil: % TPAH Depletion < 70%

15%

Oil: % TPAH Depletion > 70%

27%

Distribution of TPAH Depletion in 2007 for EL056C (Also Showing Site of Trench Dug in 2008)

NO OIL58%

2 7 %

27% 15%= No oil (includes pits with TPAH <500 ng/g sed.)

= Depletion > 70%

= Depletion < 70%%

%

66

62

TRENCH

0500

10001500

TPAH = 6000 ng/g sed.% depletion TPAH = 90.4%

TPAH = 46800 ng/g sed.% depletion TPAH = 78.8%

TPAH = 15200 ng/g sed.% depletion TPAH = 55.3%

TPAH = 22500 ng/g sed.% depletion TPAH = 48.5%

TPAH = 165 ng/g sed.

0500

10001500

0500

10001500

0500

10001500

0500

10001500

91 cm

Oil lens

56 cm

0  cm

76 cm

Depth belowSurface Cobbles

Upper Oiled“fringe”

25 cm

Lower Oiled“Fringe”

PA

H C

once

ntra

tion

(mg/

kg e

xtra

ct)

Pit Bottom

Total PAH Depletion in EL056C Vertical Trench

0500

10001500

0500

10001500

TPAH = 6000 ng/g sed.% depletion TPAH = 90.4%

TPAH = 46800 ng/g sed.% depletion TPAH = 78.8%

TPAH = 15200 ng/g sed.% depletion TPAH = 55.3%

TPAH = 22500 ng/g sed.% depletion TPAH = 48.5%

TPAH = 165 ng/g sed.

0500

10001500

0500

10001500

0500

10001500

0500

10001500

0500

10001500

0500

10001500

0500

10001500

0500

10001500

91 cm

LessDegraded SSO

56 cm

0  cm

76 cm

Depth belowSurface Cobbles

25 cmP

AH

Con

cent

ratio

n (m

g/kg

ext

ract

)

Pit Bottom

Vertical Trench at EL056C Clearly DemonstratesSequestration of SSO Residue

No SSO

HighlyDegraded SSO

Oil Sequestered with fine sand/silt

Water velocitythrough higherconductivity sediment abovesequestered oil is high

Water velocitythrough oil is very low

The Only Reason Any Oil Remains is Because It is Sequestered Within Isolated Thin Layers Containing Fine Sand/Silt

Generalized Cross-SectionOff Boulder/Cobble Shoreline

•

Oil in marine environments is subject to natural biodegradation

•

Detailed chemical analyses are needed to assess the extent of oil biodegradation and the efficacy of bioremediation•

The use of internal compounds s (e.g.C30-

hopane or C-29aaa20R ethylcholestane

[C29- stigmastane) that are resistant to biodegradation

is critical for assessing the extent of oil biodegradation following an oil spill

Summary

•

One should not expect 100% removal of a pollutant by bioremediation─Even after almost all biodegradable

hydrocarbons are consumed, up to 50% of the original oil mass may remain as inert polars

which are removed by other

weathering processes•

The process of biodegradation is relatively slow•

Biodegradative

removal takes weeks to

months to years compared to physical removal which takes hours to days

Summary

Summary

•

Bioremediation is an effective means for speeding up the rate of biodegradation–

effective for the treatment of petroleum pollutants in many, but not all, cases

–

Establishing limiting factors is critical for determining appropriate teatment

–

Applicability depends upon environment

While There Are Clear Difference Between the 1989 Exxon Valdez Alaskan Oil Spill and the 2010 Deepwater Horizon Gulf Oil Spill, There are Valuable Lessons About the Applicability of Bioremediation and What Microbial Oil Biodegradation Can Accomplish that Apply to the Current Situation

Coastal Marshes of the Gulf Coast Threatened by Oil from the

Deepwater Horizon Spill in 2010

Rocky Shorelines Heavily Oiled by Exxon Valdez Oil Spill in 1989

Extra Backup Slides

Bioremediation Index = % Loss Total PAH – 70%

Calculation of Bioremediation Index

y = 0.9103x

R2 = 0.9161

0

20

40

60

80

100

0 20 40 60 80 100

% Loss TPAH by C29R- stigmastane

% lo

ss T

PAH

by

sum

chr

ysen

es

(G)

Where: •

% loss of Total PAH is computed from ratio of (Total PAH/conserved biomarker) in sample compared to same ratio in spilled EVOS oil

•

C29R-Stigmastane was most stable biomarker

(F)y = 0.9596xR2 = 0.977

0

20

40

60

80

100

0 20 40 60 80 100% Loss TPAH by C29R- stigmastane

% L

oss

TPA

H b

y C

30-H

opan

e

Hopane Showed ~ 4% loss Sum Chrysenes Showed ~ 9% Loss

Why Use 70% for Bioremediation Index?

Depletion for 2003-2004 Prestige Oil Spill Bioremediation Test (Moreira Site)

•

Studies have shown that once lighter alkanes are removed and 60-70% of Total PAH are depleted, adding nutrients above normal shoreline background levels does not affect rate of biodegradation

(Gallego et al., 2006)

AlkanesLost

•

Amoco Cadiz study

Ixtoc-1 study

Bioremediation Indices for 2007-2008 Samples With Sufficient SSO to Quantify

(all samples with TPAH > 500 ng/g sediment)

•

Only 125 samples (16.4% of 761 total pits) had enough oil to quantify TPAH depletion

•

82.4% of those samples had positive bioremediation indices•

Overall, this indicates very low bioremediation potential

- 3 0

- 2 0

- 1 0

0

1 0

2 0

3 0

1 7 1 3 1 9 2 5 3 1 3 7 4 3 4 9 5 5 6 1 6 7 7 3 7 9 8 5 9 1 9 7 1 0 3 1 0 9 1 1 5 1 2 1

gB

iore

med

iatio

n In

dex

Bas

ed o

n C

29R

-Stig

mas

tane

Bio

rem

edia

tion

Inde

x by

Sum

chr

ysen

es

-30

-20

-10

0

10

20

30

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69

yy

Total samples = 89Fraction < 70% = 38.2%

B. NOAA 2001-2003 SCAT I, II, III

Total samples = 74Fraction < 70% = 41.9%

A. ExxonMobil Survey

Comparison of Bioremediation Indices Using Sum of Chrysenes as “Conserved” Marker for

2002 ExxonMobil and NOAA 2002-2003 Samples

0

10

20

30

40

50

60

70

80

90

100

3 M 2 M 1 M 0 MElevation Above Mean Low Tide

Most of the SSO Found in Pits in 2007-2008 Surveys Was Highly Weathered, Especially Within the BiologicallyImportant Lower Intertidal Zones (0 to 1 M Elevation)

% o

f Tot

al P

its w

ith

Tota

l PA

H D

eple

tion

< 70

% Elevation Total Pits Dug+3 meter 188+2 meter 191+1 meter 171 0 meter 163

2.0% 0.7% 0.1% 0.1%