OilSpillResearch@eng.auburn.edu
Samuel Ginn College of Engineering
Research Brief-II: Impact of Hurricane Isaac on Mobilizing Deepwater Horizon
Oil Spill Residues along Alabama’s Coastline – A Physicochemical
Characterization Study
INTRODUCTION: In an earlier brief, our environmental engineering research team at Auburn University
documented the chemical characteristics of oil residues deposited by Tropical Storm Lee (TS Lee) last
year (Clement et al. 2011). TS Lee impacted Alabama’s coast on September 2, 2011 and lingered for
over two days. Our research team was present before, during, and after the storm event. Last year, TS
Lee mobilized considerable amounts of tar balls and tar mat fragments onto Alabama’s beaches. In
general, tar balls differ from tar mat fragments based on their physical appearance: tar balls are
rounded, while tar mat fragments have unrounded, irregular edges. These unrounded, irregular edges
indicate that tar mat fragments likely fragmented from tar mats that are buried offshore, and could not
have traveled an appreciable distance before being deposited onto the beaches. Our team completed a
detailed sampling survey and characterized post-TS Lee tar balls and tar mat fragments, and compared
the Gas Chromatography and Double Focusing Mass Spectroscopy (GC/MS/MS) PAH chemical signatures
of post-TS Lee tar balls to emulsified oil (mousse) which arrived on Alabama’s beaches in June, 2010
(Clement et al., 2011). The data presented in Clement et al. (2011) confirmed that these tar balls and tar
mat fragments were formed from Deepwater Horizon (MC252) oil, and indicated that polycyclic
aromatic hydrocarbon (PAH) signatures for first-arrival oil (June 2010) and tar mat fragments mobilized
by TS Lee (September 2011) were nearly identical. Based on the observed data, Clement et al. (2011)
hypothesized that many of the PAHs trapped in submerged MC252 oil are degrading very slowly. They
also noted that post-TS Lee data demonstrated the potential for remobilization of tar mats by similar
storm events in the future. Hurricane Isaac, which impacted Alabama’s coast beginning around August
27, 2012 and continuing for several days, is one such event that allowed our team to conduct a followup study. The objective of this research brief is to provide a short summary of our initial finding related
to our post-Hurricane Isaac surveys.
FIELD OBSERVATIONS: Hurricane Isaac was a category-1 hurricane when it made landfall near the
mouth of the Mississippi River on August 28, 2012. The storm was extremely large, with hurricane-force
winds extending east along Alabama’s coastline. Our research team began monitoring Alabama’s
beaches between Perdido Pass (on the Alabama-Florida border) and Fort Morgan (on the eastern side of
Mobile Bay) starting on August 27,2012. Between August 27, 2012 and August 29, 2012, we observed
extremely energetic surf conditions and considerable sand mobilization, but no visual evidence of oil
mobilization along this shoreline. We began observing tar mat fragments and tar balls on the beach
starting on August 30, 2012 near Lagoon Pass in Gulf Shores, Alabama. This corresponded to the
reduction in surf energy along the shoreline; over the next few days oil deposition continued to occur at
several locations along this roughly 30 mile stretch of Alabama’s coastline. We completed a detailed,
two-day survey to assess the extent of deposition by manually collecting tar balls and tar mat fragments
at several previously established sampling locations, which have been periodically sampled by our team
since TS Lee. Figure 1 shows all sampling locations, and Table 1 provides specific information for
sampling locations where post-Hurricane Isaac samples were recovered.
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Mobile Bay
Fort
Morgan
Bon Secour
Lagoon Gulf shores
Park
Pass
Orange
beach
Perdido Bay
Bridge
Figure 1: Location of sampling points used in this study.
Table 1: Details of Post Hurricane Isaac Sampling Locations
S.No.
Latitude/N
Longitude/W
C0.7
30°16'14.88"
87°34'16.32"
C5.3
30°15'11.58"
87°38'38.27"
C9.5
30°14'35.48"
87°42'48.02"
C10.8
30°14'25.85"
87°44'11.01"
C12.8
30°14'7.62"
87°46'6.59"
C16.1
30°13'42.48"
87°49'23.34"
C21.2
30°13'49.86"
87°54'33.84"
Location Details
26650 Orange Beach (opposite
to St. Thomas church)
Gulf State Park beach (accessed
via Long Lane)
1109 West Beach Blvd. (near
blue bridge)
Lagoon Pass
2432 West Beach Blvd. (near
Lee’s Landing marker)
Mobile Street (Bon Secour
National Wildlife Refuge)
Morgantown Blvd (Fort Morgan)
Our team completed an extensive post-Hurricane Isaac sampling survey at the seven field sampling
locations shown in Table 1. Note the sampling point numbers (Table 1) show the distance from Perdido
Bay Bridge; for example, C10.8 is Lagoon Pass which is located about 10.8 miles from Perdido Pass. The
field survey was completed over a two day period (September 1st and September 2nd, 2012). At each of
these seven sampling location, we manually collected only the larger tar balls/tar mat fragment [quarter
size (about 2 cm) or above] deposited by Hurricane Isaac on the beaches, about 2 to 5 ft away from the
surf zone waterline, for a fixed time period of approximately 30 to 40 minutes. The size of the tar
balls/tar mat fragments collected ranged from about 2 cm to 7 cm (longest length). The amount of tar
balls (by weight) collected during this survey is shown in Figure 2. We collected approximately 25
pounds (11 kg) of tar balls and tar mat fragments; the majority were collected near Lagoon Pass
(sampling point C10.8), where we recovered about 6 pounds (2.7 kg).
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Figure 2: Amount of tar balls/tar mat fragments collected from sampling locations shown in Table 1.
Figures 3 and 4 provide examples of typical field observations made during our post-Hurricane Isaac
sampling survey. Figure 3 shows deposits of quarter-sized tar balls/tar mat fragments mixed with shells
scattered along public beaches near the mouth of Lagoon Pass, and also at the Mobile Street beach
entrance within the Bon Secour National Wildlife Refuge. This is representative of the typical tar ball/tar
mat fragment distribution pattern we observed at several other beach locations. Figure 3 also shows a
controlled survey site where we marked a 11 ft x 7 ft control area and manually collected all the tar
balls/tar mat fragments within this control area. Within this 77 ft2 area, about 150 quarter-sized
(ranging from 1 to 2 cm) tar balls with a total weight of 286 grams (about a half pound) were recovered.
Figure 3: Post-Hurricane Isaac Tar balls and tar mat fragments found along Alabama’s shoreline: a) Near the
mouth of Lagoon Pass, Gulf Shores; b) Bon Secour National Wildlife Refuge. Near Lagoon Pass we recovered
about six pounds of tar balls/tar mat fragments with size ranging from 2 cm to 7 cm within a half-mile region.
The rectangular 11 ft x 7 ft control area shown in the right image had about 150 quarter-sized (1 to 2 cm) tar
balls/tar mat fragments with a total weight of 286 grams (about half a pound).
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At the Bon Secour National Wildlife Refuge sampling location, we also observed several shell deposition
regions within the intertidal zone where large amounts of shells mixed with much smaller sized tar balls
and tar mat fragments were deposited. These tar mat fragment/tar ball mixed shell deposits in the
refuge area looked quite similar to the oil contaminated shell zones we have observed along Gulf Shore
beaches during our February 2012 sampling trip (National Geographic News, 2012). The lower right
image in Figure 4 shows one of these contaminated shell zones. The image also shows a 2 ft x 2 ft
control area, where we manually collected about 200 smaller than dime-sized (about 0.2 to 1 cm) tar
balls and tar mat fragments with a total weight of about 20 grams.
st
nd
Figure 4: Various sized tar balls/tar mat fragments found along Alabama’s beaches on September 1 and 2 ,
2012. The square 2 ft x 2 ft control area shown in the lower right image is a shell zone mixed with small, dime –
sized (about 1 cm) tar balls/tar mat fragments. The control area had about 200 smaller than dime-sized (about
0.2 to 1 cm) tar balls/tar mat fragments with a total weight of about 20 grams.
By September 5, 2012, cleanup crew began removing tar balls and tar mat fragments from Alabama
beaches and also began excavating tar mats exposed as a result of Hurricane Isaac. Estimates obtained
by coastal community officials show that between September 5, 2012 and September 11, 2012, cleanup
operations removed over 37,000 pounds of oil-tainted material from Alabama’s beaches (Orange Beach,
2012). We sent a team to observe some of these cleanup operations; Figure 5 shows these operations at
a site within the Bon Secour National Wildlife Refuge, located about a mile west of the Mobile Street
public beach, on September 11, 2012. Hurricane Isaac exposed a large tar mat at this site within the
intertidal zone. According to the cleanup crew, these operations removed over 20,000 pounds of oiltainted material from this site.
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Figure 5: Removal of tar mats exposed by Hurricane Isaac at Bon Secour National Wildlife Refuge, near Mobile
Street beach, on September 11, 2012. Over 20,000 pounds of oil contaminated sand was removed from this site.
CHEMICAL ANALYSIS: Between September 1, 2012 and September 2, 2012, we collected a large number
of relatively fresh tar balls and tar mat fragments, which were mobilized and deposited by Hurricane
Isaac, at several of our beach sampling locations (Figures 1-3; Table 1). Most of the largest tar balls and
tar mat fragments were found in the vicinity of Lagoon Pass and some of these samples are shown in
Figure 6. The field samples collected after both TS Lee and Hurricane Isaac had a strong hydrocarbon
odor and a similar visual appearance. In our laboratory, we have archived emulsified oil (mousse)
samples from the first arrival of oil on Alabama’s beaches (collected in June 2010), and tar ball and tar
mat fragments from post-TS Lee (collected in September 2011); addition of post-Hurricane Isaac
samples to this archive provided an opportunity to both physically and chemically compare samples
from these three distinct time periods.
Tar ball and tar mat fragment samples were analyzed at our
National Science Foundation (NSF) funded oil testing laboratory
equipped with Agilent technologies triple quadrupole
GC/MS/MS (7000B). For PAH analyses, the system was run in
multiple reaction monitoring (MRM) mode. Hopane
fingerprinting analysis was run in the selected ion monitoring
(SIM) mode. The GC/MS/MS system is equipped with a high
sensitivity electron impact ionization source (EI), a collision cell,
and a back flush which reduces background noise and improves
sensitivity across the entire mass ranges selected in the
Figure 6: Post Isaac Tar balls and tar experiment. Field samples were extracted and cleaned up using
standard laboratory methods. An organic solvent mixture
mat fragments collected within a
(consisting of hexane and dichloromethane in 3:1 ratio) was
150-ft region from the Lagoon Pass
used to separate the oil from inorganic sand and shell materials.
outlet.
Both post-TS Lee and post-Hurricane Isaac samples contained
about 80% sand and shells, and the mousse (June 2010 sample) did not contain any shells or sand. For
the GC/MS/MS-based PAH analysis, we extracted a known amount of mousse and tar ball samples using
20 ml of the solvent mixture. The sample weights were adjusted such that the total amount of oil
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extracted from all three samples was the same. A similar extraction procedure was used for hopane
analysis, but with the exception that pure hexane was used as the extraction solvent. The final samples
were spiked with isotopically-labeled internal standards prior to analysis. All measurements were
repeated at least three times to verify the reproducibility of the analytical method. Quantification of
PAHs was made using calibration samples prepared from Supelco EPA-PAH standard mix purchased from
Sigma-Aldrich Inc.
Figure 7 compares the MRM total ion chromatogram of the first arrival mousse (June 2010) with
the post-TS Lee sample (September 2011) and the post-Hurricane Isaac sample (September 2012). The
figure shows that the MRM chemical signatures of all three samples are essentially identical.
Figure 7: Comparison of GC/MS/MS MRM fingerprints of PAHs in first-arrival mousse (blue), post TS Lee tar ball
(red), and post-Isaac tar ball (green) samples.
Figure 8 compares the concentrations of various PAH constituents measured in the new post-Hurricane
Isaac sample with the PAH values previously quantified in the first-arrival mousse and post-Lee samples.
The data show that the concentration of selected PAH compounds in all three samples are remarkably
similar, indicating that the PAH concentrations have not changed greatly over the past two and a half
year period. In fact, some of the PAHs appear to be concentrating within tar mat. For example, the
concentration of chrysene measured in post-TS Lee and post-Hurricane Isaac samples are slightly higher
than the chrysene concentration levels measured in the first arrival sample.
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Figure 8: Comparison of PAH concentration levels measured in the first-arrival mousse (blue), TS Lee tar ball
(red), and Hurricane Isaac tar ball (green) samples.
Figure 9 shows the hopane fingerprints of the three samples (SIM at m/z 191). The figure shows that
the hopane chromatogram patterns are identical, indicating that the oil in all three samples originated
from the same source (weathered MC252 oil).
IMPLICATIONS OF THE STUDY AND SOME UNANSWERED QUESTIONS: Our results indicate that
emulsified oil, which arrived on Alabama’s beaches in June 2010, and the tar balls and tar mat fragments
which appeared on Alabama’s beaches after TS Lee (September 2011) and Hurricane Isaac (September
2012), have essentially identical MRM total ion chromatograms (GC/MS/MS PAH fingerprints). In
addition, hopane fingerprints for all three samples are essentially identical. Moreover, the
concentrations of PAHs in the samples collected post-TS Lee (2011) and post-Hurricane Isaac (2012) are
not substantially different from the same PAH concentrations in the emulsified oil which first arrived on
Alabama’s beaches in 2010.
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Figure 9: Comparison of hopane fingerprints (SIM at m/z 191) of first-arrival mousse (blue), post TS Lee tar ball
(red), and post-Isaac tar ball (green) samples.
When considering the consequences of the Deepwater Horizon catastrophe on Alabama’s coastline,
several important questions arise. These include: when will Alabama’s beaches fully recover to their
pre-spill baseline (free from MC252-related tar balls and tar mat fragments)? What are the long-term
environmental and ecological impacts? These and other questions continue to be raised by coastal
residents, tourists and policy-makers, all of whom depend on the aesthetics, health and safety of
Alabama’s beaches. Alabama’s tourism industry was negatively impacted in 2010 as a result of
Deepwater Horizon oil inundating Alabama’s beaches (Hayworth et al. 2011; Hayworth and Clement,
2012). Over the past two and a half years, much of the oil which was present on the beaches as a result
of the first arrival event has been removed by both natural and human means (Hayworth and Clement,
2011), and therefore, under normal conditions, the presence of tar balls on the beaches are much less
noticeable to the average beach-goer. However, as TS Lee and Hurricane Isaac have revealed,
mobilization and re-deposition of oil onto the beaches continues to be a lasting consequence of the
Deepwater Horizon catastrophe. It is very likely that the source of the oil mobilized and deposited on
Alabama’s beaches post-TS Lee and Hurricane Isaac are subtidal, buried tar mats, existing in the
nearshore areas along Alabama’s beaches. Technological challenges associated with locating and
removing these tar mats makes this a long term problem for local governments. Because we have no
real understanding of the magnitude and distribution of nearshore tar mats, and because we have a
limited understanding of the processes which lead to mobilization and re-deposition, it is currently not
possible to predict with any certainty how long this mobilization and re-deposition cycle will continue.
Fortunately, under normal weather conditions, mobilization and re-deposition of tar balls and oil
fragments is of a magnitude deemed acceptable by the average beach-goer. However, it is important to
realize that this low magnitude mobilization and deposition itself is several hundred times higher than
the original baseline of zero for this type of relatively fresh sticky tar balls having strong hydrocarbon
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odor. With regard to the “total tar ball” baseline, it is possible to occasionally encounter some highly
weathered non-MC252 related tar balls on Alabama’s beaches. However, as noted in Unified Command
(2011), these rare non-MC252 related tar balls are comprised primarily of high molecular weight
asphaltenes, contain very little to no sand, are usually very hard, and have a very weak petroleum odor
(often no odor). In contrast, MC252-related tar balls are a fragile, soft, sticky brownish material
containing a considerable amount of sand, and a very noticeable petroleum odor and hence are easy to
identify (Unified Command, 2011). In fact, to our knowledge, no one has found a tar ball on Alabama’s
beaches having the physical characteristics of MC252 tar balls but not in fact being a MC252 tar ball.
Therefore, without detailed chemical analysis it is safe to conclude that the fragile, sticky tar balls and oil
fragments currently found along Alabama’s shoreline are all Deepwater Horizon-related tar balls and oil
fragments. In our opinion, local communities should not be burdened with proving the chemical origin
of these tar balls and oil fragments; rather it should be the responsibility of BP to prove an alternative
origin for these tar balls if they consider that a possibility.
It is also important that efforts be made to define tar ball baseline levels (or background) for
Alabama’s beaches that existed prior to the spill. The Unified Command (2011) shoreline cleanup
completion plan attempted to develop a rationale for defining a cleanup endpoint to determine when
removal actions can be deemed complete. The report states: “Although the highest clean-up endpoint
is removal of all visible oil, this is often impossible particularly if there is a background rate of oil
deposition. In these cases, the more appropriate endpoint would be to cleanup visible oil, but not
exceeding the background amount. For sandy beaches, clean-up can be terminated when no visible oil
remains on the surface, except for scattered tar balls or swash lines of minute tar balls which may occur
as the sand is reworked by the waves. All tar balls that can be removed by reasonable cleanup
techniques, or that can be remobilized, should be removed. Remaining tar balls should be at or below
normal background frequency.” The plan also summarizes the results of a field survey completed
between April 3, 2011 and October 7, 2011 (over a six month period) that recorded about 680
occurrences of non MC-252 tar balls on the shorelines of the four impacted Gulf States (Texas,
Louisiana, Mississippi, Alabama, and Florida), covering approximately 500 miles. This dataset implied
that Deepwater Horizon-impacted northern Gulf of Mexico beaches have a background tar ball level
resulting from a number of non-Deepwater Horizon-related sources (for example, natural seeps, leaks
from existing wells and pipelines within the Gulf of Mexico, leaks from vessels operating within the Gulf
of Mexico, etc.). However, it important to note this collection was made over a 500-mile long coastline
over a six-month period: based on these data one can estimate that the background tar ball activity is
indeed very low; only about 5 tar balls per mile of northern Gulf of Mexico shoreline. Our field
observations have indicated that the current level of MC252 related tar ball activity is at least two to
three orders of magnitude higher than this baseline value. For example, as shown in Figure 4, on
September 1, 2012, we collected about 150 quarter-sized tar ball in a 11 ft x 7 ft region within
approximately 30 minutes. Also, it is important to note that typical background tar balls (i.e., nonMC252 tar balls) recovered from Alabama’s shores are highly weathered, predominantly black
asphaltenes; to our knowledge, no one has recovered fragile, sticky, relatively fresh non-MC252 tar balls
with strong petroleum odor from the Alabama shoreline, at least within the past 3 years.
The results of our ongoing study are relevant to potential long-term ecological consequences for
Alabama’s beaches beyond the recognized nuisance related to the presence of sticky tar balls on white
sandy beaches. Our observations show that MC252 tar balls and tar mat fragments appearing on
Alabama’s beaches (both at relatively low frequency under normal weather conditions, and also at much
higher frequency following high energy storm events) contain a number of hazardous PAH compounds
at concentrations essentially the same as the oil which first arrived on these beaches nearly three years
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ago. The ecological implications of this fact remain uncertain. However, what is certain is that these
partially weathered tar balls and tar mat fragments contains PAH compounds at concentration levels
essentially the same as those originally present in the emulsified oil (mousse) which first arrived on
Alabama’s beaches in June 2010. These partially weathered tar balls and tar mat fragments likely
originated from submerged deposits of unknown location and extent, trapped within the nearshore
beach system.
In summary, it is important to recognize and acknowledge that Alabama’s beaches have not fully
recovered, and that the beach ecosystems have been and continue to be impacted by the Deepwater
Horizon catastrophe in ways we do not yet fully understand. How these impacts will manifest
themselves both physically and ecologically over time is also not fully understood. Perhaps, Former
Defense Secretary Donald Rumsfeld words best summarize the current situation: “There are known
knowns; there are things we know that we know. There are known unknowns; that is to say there are
things that, we now know we don't know. But there are also unknown unknowns – there are things we
do not know, we don't know.” Thus this situation requires prudence, healthy skepticism, and continued
scientific inquiry.
DISCLAIMER: The results presented here do not constitute a human health assessment.
AUTHORSHIP AND ACKNOWLEDGEMENT: This study was completed by Dr. T. P. Clement, Groome Jr.
Endowed Distinguished Professor of Environmental Engineering (clement@auburn.edu), Dr. J.S.
Hayworth, Associate Research Professor of Environmental Engineering (jsh@auburn.edu), Dr. V.
Mulabagal, Research Associate, Mr. G.F. John, Graduate Research Assistant, and Mr. F. Yin, Graduate
Research Assistant. This work was supported in part by funding received from the City of Orange Beach,
Alabama. The GC/MS/MS facility and characterization methods were developed from grants funds
received from the National Science Foundation (NSF), Samuel Ginn College of Engineering, and Marine
Environmental Sciences Consortium (MESC).
REFERENCES
Clement, T.P., J.S. Hayworth, V. Mulabagal, G.F. John and F. Yin (2011). Research Brief-I: Is Submerged Deepwater
Horizon Oil Degrading Offshore? Comparison of the Chemical Signatures of Tar Mat Samples Deposited by Tropical
Storm Lee in September 2011 with Oil Mousse Samples Collected in June 2010. Released on September, 20, 2011.
http://www.eng.auburn.edu/files/acad_depts/civil/oil-spill-research.pdf
Hayworth, J. S. and T. P. Clement. (2011). BP’s Operation Deep Clean: Could dilution be the solution to beach
pollution? Environmental Science & Technology, 45, 4201–4202.
http://pubs.acs.org/doi/pdf/10.1021/es201242k.
Hayworth, J. S., T. P. Clement, and J. F. Valentine. (2011). Deepwater Horizon oil spill impacts on Alabama beaches.
Hydrology and Earth System Sciences Journal, v. 15, p. 3639–3649. http://www.hydrol-earth-systsci.net/15/3639/2011/hess-15-3639-2011.pdf
Hayworth, J.S. and T.P. Clement, (2012). Provenance of Corexit-related chemical constituents found in nearshore
and inland Gulf Coast waters, Marine Pollution Bulletin, In press,
http://dx.doi.org/10.1016/j.marpolbul.2012.06.031
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National Geographic News (2012), National Geographic News story on our beach sampling efforts, published on
May 22, 2012: http://news.nationalgeographic.com/news/energy/2012/03/120322-gulf-oil-spill-tar-balls-wash-upon-beaches/ (accessed on September 16, 2012).
Orange Beach (2012), Estimates of tar ball collection after Hurricane Isaac; preliminary assessment report
submitted by Alabama State On-scene coordinator to the City of Orange Beach.
Unified Command (2011), Shoreline clean up completing plan. Published by the Unified Command SCCP Core
Group, November 2011 report. P.39. http://www.restorethegulf.gov/sites/default/files/u306/Signed%20SCCP1.pdf
(accessed on September 16, 2012).
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