Download Petroleum Hydrocarbons: A Survey of Structures, Weathering, and

Petroleum Hydrocarbons:
A Survey of Structures, Weathering, and Remediation
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Abstract:
Man’s history with the petroleum industry has produced many geographically distinct, and highly
damaging hydrocarbon releases. Among these occurrences, the most influential to the environment
include source “point discharges contaminated by urban runoff, refineries, and other coastal
effluents”(1). These tend to cause chronic pollution problems primarily within and around the
coastal areas where such point sources are identified. More quantifiably extreme spills and
discharges have occurred from tankers, while crude or refined petroleum has been in oceanic transit.
These latter instances occur with much less frequency, however the shear magnitude of released
petroleum invokes immediate threats to the surrounding ecosystems (2). Discharges and spills
within the past decade alone have included:
1989: Exxon Valdez - 0.04 megatons into Prince William Sound, AK
1990: Apex Barge - 3,000 cubic meters in Galveston Bay, TX
1990: Mega Borg - 45 cubic meters off Texas coast
1991: Haven - 0.14 megatons off Italian coast
1991: Gulf War - 0.82 megatons deliberately released in Kuwait by Iraq
1993: Braer - 0.08 megatons along the coast of the Shetland Islands, UK
(cited in Swannell et. al.(2))
As a result of such petroleum releases into the environment, emergency measures are required to try
to alleviate the impending damage to local ecosystems. Government agencies and scientists have
long studied the natural effects of weathering upon petroleum. Results of these studies have
provided insight into possible anthropogenic enhancements to natural weathering, while
subsequently creating viable support methods to physical cleanup measures. It is the goal of this
paper to provide a clear understanding of petroleum as a damaging pollutant to the world’s marine
ecosystems. Focus will be placed upon the roles which both natural and anthropogenic influences
play in the remediation of petroleum spills, as well as studies aimed at determining the affects of
these influences.
Petroleum Structure:
In order to possess a good understanding of petroleum as an environmental pollutant, it is beneficial
to first understand the complex chemical identity and structure of this organic material. In fact,
petroleum obtained from different geographic locations is likely to possess chemical compositions
which are highly specific to those areas (3). Primary to all raw petroleum (known as crude oil) is the
hydrocarbon structure, or C-H bonding pair. This backbone component is isolated from centuries of
pressure and temperature acting upon sedimentary layers of dead organic matter (1). Multiple C-H
bonds will combine to form an array of hydrocarbon compounds, of which three main classes have
been identified:
1. Aliphatic hydrocarbons
2. Alicyclic hydrocarbons
3. Aromatic hydrocarbons
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Aliphatic hydrocarbons are open-chain compounds in which the linked carbon atoms may contain
single (saturated) bonds, or any combination of double and triple (unsaturated) bonds (4).
Characteristically, carbon possesses four valence, bonding electrons. Hydrogen is generally an
opportunistic bonding atom, and will bind to those valence electrons which have not been utilized by
the carbon-carbon chain. Based upon their complexity, aliphatic hydrocarbons may contain as few a
two carbons (ethane), or stretch continuously, possessing greater than 78 carbons in a single chain
(1).
Examples of aliphatic hydrocarbons:
H2C
C C CH
H
1-Buten-3-yne
H2C CH2
H3C CH3
Ethane
Ethylene
Alicyclic hydrocarbons will contain ring structures, often comprised of five to six, saturated or
unsaturated, carbons. These compounds can appear highly complex in their arrangements of carbon,
especially when multi-ringed structures are present (4).
Examples of alicyclic hydrocarbons:
HC
HC
H2
C
CH
H2
H2
C H C
H2C
C
CH2
CH
H2C
C
H2
1,4-Cyclohexadiene
C
CH2
C H C
H2
H2
Decahydronaphthalene
H
C
H2C
CH
C C
H2 H2
Cyclopentene
Characteristic of aromatic hydrocarbons is the presence of at least one 6-carbon benzene ring, the
structure which separates these compounds from alicyclic hydrocarbons. This benzene may be
joined with aliphatic chains, alicyclic structures, or as a combination of benzene rings either linked
aliphatically or fused into compounds known as polycyclic aromatic hydrocarbons (4).
Examples of aromatic hydrocarbons:
C
H
C
H
1,2-Diphenylethylene
Anthracene
Aliphatic and alicyclic hydrocarbons are, by themselves, most prevalent in crude oil, and are often
quantitated by gas chromatography techniques to evaluate the total concentration of spilled
petroleum (5). Aromatic hydrocarbons, although posing the greatest threat to our environment, tend
to exist in much lower concentrations. In addition, the more volatile aromatics, such as benzene and
toluene, will generally degrade rapidly following a petroleum release (5). This is due to
characteristically high vapor pressures and polarity which leaves them susceptible to evaporation and
dissolution into the air and surrounding water. Degradation of crude oil will act less favorably upon
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the decomposition of more complex aromatics, particularly the polycyclic aromatic hydrocarbons
(PAH). As a result, PAHs have been utilized extensively in monitoring degradation and toxicity
levels, as well as in the source-fingerprinting of oil spills (5). Determinations of the latter can prove
valuable in terms of litigation aimed at punishing those responsible for an oil spill or discharge (6).
Certain other elemental compounds can be found within petroleum, most of which are considered to
be impurities by the petroleum industry. The presence of sulfur has been demonstrated to be
corrosive, malodorous, and poisoning to the daily operations and equipment found in petroleum
refineries (7). Nitrogen is also present, often in the form of pyridine and its derivatives. When
refined, both of these components tend to become concentrated at high boiling fractions (7). This
poses a hazard regarding safe, effective processing and removal of these impurities from petroleum
end products. Oxygen may also exist in the form of functional groups attached to hydrocarbons (7).
The characteristically dark color of petroleum is produced as a result of these elemental compounds,
as well as the presence of metals such as vanadium, nickel, cobalt, and iron. These metals exist in an
apparent colloidal suspension within the complex of hydrocarbons, and is likely to be resulting in
atmospheric particulate pollution during petroleum refinement (7).
Petroleum Weathering and Anthropogenic Influences:
Hydrocarbons can be found occurring naturally throughout the marine environment, including forms
not derived from petroleum. Marine plankton, for instance, produce and release a yearly average
four to eight times the amount of hydrocarbons originating from petroleum (1). Yet concern over
such naturally occurring hydrocarbons remains low due to their gradual release throughout the year,
and their high rates of weathering. It is the accidental and deliberate release of petroleum by man
which poses the greatest threat to the environment. When these releases occur, concentrations of
hydrocarbons tend to be far too overwhelming for the natural responses of weathering and
degradation to be affective. There arises an evident shift in environmental equilibrium towards toxic
levels of pollution.
Six primary hydrocarbon weathering patterns occur within the natural environment, as illustrated in
Freedman (1):
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Among these, four become patterns of distribution. Within the first six to ten hours following an oil
spill or discharge, dispersion of the resulting slick will act to gravitate the oil outward to a thickness
at or below 0.1mm on the surface of the water (7). Frictional forces have been known to counteract
this dispersion. Due to the tremendous amounts of oil released from a spill, this often becomes
advantageous in terms of containment for physical clean-up purposes. Aiding in this friction, long,
floating oil barriers, known as booms, are often utilized by emergency clean-up crews to prevent a
spill from spreading towards shorelines and incurring immediate damage upon local wildlife.
Methods for oil containment have also involved the use of high pressure water jets, capable of
producing enough force to deflect oncoming oil slicks (8). Simultaneous to these containment
efforts, crews will begin physical collection procedures. Utilizing large surface skimmers, they work
quickly to gather and contain as much of the floating oil as possible (9). Unfortunately, recovery of
large quantities of petroleum by this method is only feasible within the window of containment
governed by the oil’s natural distribution (9).
Evaporation will remove the more volatile components of an oil slick with the aid of temperature,
wind speed, and water turbulence (1, 7). These hydrocarbons, which can constitute 20 to 50% of
most crude oils, are generally lower in molecular weight, and of higher vapor pressure (1, 7).
Hydrocarbons which are vaporized, may then undergo degradation in the atmosphere. However,
some will enter the atmosphere as aerosols, only to be redeposited in the future (7). Those
hydrocarbons which are not volatilized can sometimes be dissolved within the surrounding water or
deposited into the local sediment. Dissolution will tend to favor hydrocarbons which possess higher
degrees of surface area (such as aromatics), lighter molecular weight, and polar characteristics (1, 7).
As with dispersion, the natural processes of evaporation and dissolution can prove detrimental to the
environment. Although less toxic hydrocarbons may be evaporated or dissolved, only time will
allow the overwhelming concentrations of these hydrocarbons to become distributed below
environmentally damaging levels.
The final distribution process of hydrocarbon weathering is emulsion, or the colloidal dispersions of
oil into water and water into oil (7). The first formation (oil-in-water) will often reduce the oil to
fine droplets, possessing relatively large surfaces areas (7). This can become beneficial to future
chemical and biological degradation. However, the residence time for this type of emulsion is often
low due to the natural hydrophobic properties of oil. It is the sulfur, nitrogen, and oxygen containing
compounds naturally found in petroleum which will often aid in maintaining these emulsions. Such
compounds tend to be polar, and hydrophilic by nature. As a result of this positive action,
anthropogenic clean-up methods have adopted similar chemical dispersants, or surfactants (7).
Treating spilled oil with detergent or fertilizer-based compounds, emergency crews attempt to
promote oil-in-water emulsion, and subsequent degradation processes (7).
Unfortunately, the anthropogenic treatment of oil with surfactants is currently being regarded as
having dangerous repercussions. Fatalities in marine bird populations, as a result of petroleum
exposure, has also been linked to these surfactant. An examination was performed, which
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considered the effects of hydrocarbon ingestion on marine bird immune systems (3). First order, or
direct ingestion of petroleum was specifically linked to the oiling of feathers which tended to cause a
degradation in the feather’s natural capacities: water repellency, insulation, and plumage (3). It is
believed that emulsion-promoting surfactants added to a spill will also bind to the waxy,
hydrophobic feathers of marine birds, producing a greater affinity for the feathers to accept water.
As an instinctive function of these losses, birds will begin preening their feathers, and subsequently
ingest high levels of hydrocarbons. Aside from the large numbers of fatalities, hydrocarbon
contamination of marine birds has resulted in many different physiological problems including
hypothermia, dehydration, infection, arthritis, eye irritation, and gastrointestinal disorders (3).
Water-in-oil emulsions produce the reverse effects of oil-in-water emulsions. They tend to exist with
comparatively lower surface area and a high residency rate. Degradation of such emulsions is
reduced, and the risks of this mousse-like substance affecting shoreline habitats is greatly increased
(1, 7). In coastal regions, these emulsions will eventually touch land, coating the shoreline in thick
oily residue, and mixing with the local sediments (1). Cleanup efforts for this shoreline damage will
usually begin with the physical collection and removal of petroleum. According to Prince,
contaminated sand is often dug into a network of trenches (9). The surrounding oil is then scraped
into these trenches, vacuumed into large collection trucks, and hauled away from the spill site.
Rocky coastlines utilize a separate technique in which the oil is “wash[ed] back into the sea and
collect[ed] with skimmers”(9). Throughout these mechanical processes, workers will also walk the
exposed shorelines, manually raking and removing oil-laden sediment and rocks (10). Based upon
the extent of remaining oil residue, decisions will then be made whether to allow only natural
weathering processes to continue the cleanup, or to incorporate anthropogenic methods of
hydrocarbon degradation, such as bioremediation.
Photochemical-oxidation and biodegradation are two natural processes which chemically
transform hydrocarbons. Photochemical-oxidation, as its name implies, is the chemical restructuring
of hydrocarbons in the presence of light and oxygen (7). Commonly, oxygen functional groups will
form, as oxygen from the surrounding air and water continually bombard hydrocarbons. As this
continues, polarity of these new compounds will increase, making them more water soluble and,
subsequently, more susceptible to biodegradation (7). Unfortunately, photo-oxidation of the waterin-oil emulsions will often result in floating tar balls which, when mixed with sediment, will take on
asphalt-like properties (3). This can develop into oceanic pollution promoted by circulating current
systems. A study performed in 1973 in the Sargasso Sea estimated the accumulation of nearly 65
thousand tons of this tar (1).
Biodegradation is currently the most widely studied process by which hydrocarbons are chemically
transformed into more useful compounds. The primary agents for these transformations are
microorganisms such as bacteria and fungi (11). Bacteria will usually become the most prominent
hydrocarbon-degrading organisms during an oil spill. This is due to the largely numbered and
diverse species capable of residing and proliferating throughout the earth’s water systems. Indeed, it
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is this water which is required to transport bacteria to a spill site as well as maintaining a medium in
which they may survive. Hydrocarbons, although a prime carbon and energy source, cannot provide
a viable substrate for bacterial growth (7). When an oil spill reaches local shorelines, it is the
sediment indigenous to the area which tends to become a breeding ground for bacteria. Sufficient
levels of bacterial nutrients, such as nitrogen and phosphorous, must also be available in and around
an oil spill site to accommodate continual bacterial growth and enrichment (7, 11).
As the natural weathering processes of dispersion, dissolution, and oil-in-water emulsion begin to
distribute hydrocarbons within the water column, indigenous strains of bacteria will simultaneous
move to oxidize and utilize these organic chemicals. The choice and speed of these transformations
tend to be based upon the complexity of the hydrocarbon. As mentioned previously, polycyclic
aromatic compounds will degrade much slower than lesser aromatics or straight-chain aliphatics,
making them a good source for monitoring overall degradation levels (5). During microbial
transformation, oxygen from the environment and the respiratory agent NADH, which is found in
bacteria, will collectively contribute an [OH] group to the hydrocarbon structure, thereby displacing
a hydrogen (7). Further addition of NADH and enzymes, along with oxygen or water depending
upon the hydrocarbon, will continue to transform the molecule until a viable or less harmful product
is created (7). Carbon dioxide is most often produced, as well as Acetyl CoA and Succinyl CoA
both of which contribute to the Krebs cycle of respiration (7).
In the presence of naturally occurring hydrocarbons, indigenous bacteria are generally well adapted
to these structures, as well as to their surrounding climatic and nutrient conditions. As a result, these
bacteria will readily transform such hydrocarbons (11). However, spilled petroleum contains a
complex of hydrocarbon structures, many of which are foreign and cannot be degraded by local
bacteria strains (11). Also, the magnitude and concentration of a spill requires vast numbers of
degrading bacteria, and the nutrients to sustain such numbers. As a result, scientists have embarked
upon efforts of bioremediation to try to increase the affects of microbial degradation.
Microbial seeding has become a topic of studies aimed at introducing known petroleum-degrading
bacteria to a spill site (11). There is a great deal of controversy surrounding this technique,
particularly whether or not seeding actually produces beneficial results. For example, following the
1990 discharge of more than forty-five cubic meters of crude oil off the coast of Texas, two sections
of the resulting slick were treated with a commercial microbial agent (2). Visual observations
following the application noted an apparent color change indicative of petroleum dissipation.
Furthermore, testing for the presence of hydrocarbons demonstrated significantly lower levels than
the spill concentration indicated. However, chemical testing was inconclusive with regards to the
effects of microbial decomposition. Absolute determinations of the fate of the petroleum could not
be ascertained as a result of open water testing. Variables for this indetermination included nonuniform application of the bacteria, and imprecise sampling due to currents and water column
shifting. There also existed a limited window for analysis before the slick ultimately dissipated
beyond the test site, as a result of natural weathering (2).
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Concern also exists regarding the by-products of bacteria hydrocarbon digestion. Sulfur, for
example, is a naturally occurring element in many forms of petroleum. Degradation of such
petroleum by certain bacteria have been known to produce hydrogen sulfide (H2S) as a by-product.
Hydrogen sulfide is, itself, a poisonous gas capable of harming organism respiratory function
including that of humans. Also, it has been linked to metal corrosion, which may lead to the
degradation of ship hulls and petroleum pipelines (12). Such degradation raises concern over
possible discharges of petroleum. In an effort to reduce these concerns, biotechnology organizations
have begun to develop biocides capable of destroying petroleum-digesting bacteria. Tetrakis
hydromethyl phosphonium sulfate (THPS) is one such biocide developed by the Albright and Wilson
Company. Its main constituent is a phosphonium salt which breaks down bacteria while at the same
time degrading into a non-toxic form (12). Unfortunately, a paradox results from the persistence of
hydrocarbons in the aftermath of bacterial eutrophication.
Nutrient applications have become another topic of scientific investigation in and around spill sites.
As discussed previously, surfactants and fertilizers are rich in elements such as nitrogen and
phosphorous. Bacteria, often considered the micro flora of the plant world, require these elements to
stimulate bacterial growth and processes such as hydrocarbon degradation (7). Probably the most
widely acknowledged, and extensively studied spill site in the United States is the area in and around
Prince William Sound, Alaska. In March 1989 the Exxon Valdez ran aground, spilling roughly
41,000 cubic meters of crude oil into the sound (2). Following a year of physical clean-up responses
and winter weathering conditions, the National Oceanic and Atmospheric Administration made the
determination that in addition to natural weathering, the remaining oil would be subjected to
bioremediation processes of fertilization (2). This would become the most detailed study of large
scale, on-site bioremediation performed to date.
Initial laboratory examinations utilized gas chromatography/mass spectroscopy (GC/MS).
Determinations were made of the rates at which microorganisms, indigenous to the sound, worked to
degrade samples of the crude oil released by the Valdez. Also examined were carbon dioxide (CO2)
production, oxygen (O2) consumption, and the formation of radioactive labeled CO2 from initially
labeled aromatic hydrocarbons (2). The experiments verified the existence an abundance of
available microorganisms capable degrading the majority of hydrocarbon components (2). Further
analysis indicated that the available nutrient systems, namely nitrogen and phosphorous, helped to
stimulate this degradation. It was decided, therefore, that the remaining shoreline oil would be
subjected to nutrient fertilizing in an attempt to advance the rates at which the oil was being
degraded (2).
Treatment sites were chosen along shorelines that had been particularly inundated with persistent
oily residues. The sites were then subdivided into separate areas based upon their sediment
compositions: sand, gravel, and cobble (2). Treatments consisted of a number of commercially and
naturally derived fertilizers, each of which was administered to a separate site to allow for
comparison of results (2). Untreated, control plots were also designated throughout the studies (2).
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Samples from each of the plots were continually retrieved over designated time points, and their
hydrocarbon profiles were measured using GC/MS. Bioremediation success would be based upon a
multiple regression analysis of the ratios of known degrading hydrocarbons to known non-degrading
hydrocarbons, or biomarkers (2).
Immediate results from these studies appeared to be inconclusive from the standpoint of biomarker
comparisons. Although both visual and analytical data suggested significant remediation of
hydrocarbons in the experimental sites, the branched aliphatic hydrocarbons which were utilized as
biomarkers appeared to be degrading just as readily (2). It was decided that further treatment and
study would be necessary, utilizing a more persistent alicyclic hydrocarbon known as hopane (2).
Conclusions to these secondary studies confirmed the initial results. When compared to the control
sites, overall hydrocarbon degradation within the fertilized sites had increased two to seven times.
Comparisons made between the various fertilizers, however, were inconclusive due to application
differences, and tidal washes of some of the treatment material (2).
Overall, the studies performed in Prince William Sound provide valuable data favoring the use of
bioremediation techniques. Although the speed of these techniques is certainly deemed inferior to
that of rapid physical cleanup measures, the process itself is beneficial to maintaining coastal habitat
structures (2). It is also a method by which hydrocarbons may be degraded into less toxic forms
rather than simply being shifted and distributed throughout the environment. Ultimately these
studies add to the network of information surrounding bioremediation. Seeding and fertilizing
remain as relatively new concepts for which many more studies must be performed in hopes of
eventually designing standard, universal methods for the bioremediation of spilled petroleum.
Issues of Study Validation and Conclusions:
An article was recently issued by the National Marine Fisheries Service (NMFS) which provides a
strong assessment of techniques for monitoring the effects of hydrocarbon ingestion by marine biota
(6). Past studies have shown that “fish and other marine vertebrates can efficiently metabolize
aromatic compounds in their livers, and then excrete the metabolites, primarily into bile”(6). This is
positive evidence that the edible flesh of these vertebrates remains relatively uncontaminated, and is
subsequently fit for human consumption. Conversely, it has been demonstrated that invertebrates
such as lobster and shellfish are likely to ingest and retain toxic hydrocarbons, particularly aromatics,
within their edible tissues (6). This stems from a decreased efficiency of metabolic activities in such
species. As a result, the threat of contamination due to human consumption (as well as other higher
trophic organisms) is deemed to be much greater.
The development and conclusions of this study, as with any study, have to be fully evaluated in terms
of defining the study parameters, analytical performance, and the quality and reliability of data.
Furthermore, it is necessary to determine whether or not a prescribed study will actually contribute,
in whole or part, to answering the questions being raised. In their report for the NMFS, Krahn and
Stein focus upon a tiered system of analysis, designed to minimize costs and time consumption
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without sacrificing high quality results (6). Primary to this system is an evaluation and determination
of the questions to be answered by the study. With regards to species toxicity, there are a number of
directions that a study may take. Preliminary source identification is important in determining which
hydrocarbon forms are most prevalent in the spilled petroleum. Ascertaining this information can
help to filter out background sources, and gain evidence against responsible polluters (6). As
discussed earlier, PAHs are of particular concern, both in terms of higher toxicity and longer
residence time than other forms (5). These characteristics promote PAHs as important candidates for
the analytical hydrocarbon analysis of local species, and sediments.
Throughout a study, sampling must take on a statistical approach in order to produce a concise,
viable representation of a sampling area. Time becomes a factor in sampling any petroleum spill due
to varying concentrations and depositing of hydrocarbons throughout the life of the spill. Krahn and
Stein stress the importance of a “rapid response” in determining initial study parameters and
obtaining appropriate samples for analysis (6). Once sources and prevailing hydrocarbon structures
have been identified, sampling and testing of local species can open further questions regarding the
health risks affecting those species, as well as possible hydrocarbon transfer to higher trophic levels.
In terms of quality assurance a “sampling plan must also contain information about how the samples
will be tracked, transported, and stored, as well as steps that will be taken to prevent contamination
or loss of analytes during sampling and storage”(6).
In continuing with a tiered approach, analytical analysis can begin with a general screening of
samples to determine the presence and estimated concentrations of various hydrocarbon forms. For
example, Krahn utilized size-exclusion HPLC techniques to analyze over 400 sediment samples
taken throughout the Exxon Valdez spill site in Prince William Sound, Alaska (6). In comparing the
resulting chromatograms with known HPLC profiles, complex hydrocarbon compounds were able to
detected, and possible sources identified. Likewise, HPLC profiles can be obtained from fish and
invertebrate tissues to gain estimated identities and concentrations of hydrocarbons. In such
experiments, HPLC identification provides a rapid, cost effective evaluation of contamination,
enabling officials to make immediate response decisions regarding health threats to local species as
well as continued species harvesting for human consumption (6).
Once petroleum contamination has been confirmed, specific identification and respective
concentrations may be assessed utilizing more costly approaches. Krahn recommends the use of gas
chromatography and mass spectroscopy (GC/MS) for this purpose (6). In studying aromatic
concentrations in several bottom-dwelling fish species in the Exxon Valdez spill area, GS/MS
verified high levels within the bile of these species (6). However, levels remained consistently low
within the edible flesh, a determination which became extremely important in allowing commercial
fishing lanes, as well as recreational fishing sites, to remain open (6). In 1996, following the spill of
the North Cape barge off the Rhode Island coast, similar GC/MS techniques were used to identify
the extent of contamination to the local shellfish population (6). Due to their more primitive
metabolism, much higher levels of aromatics were found within the edible flesh of such species.
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This resulted in continual monitoring of the site, using both screening and specific techniques, to
determine the eventual reopening of the area to harvesting (6).
Although studies involving the effects of petroleum release are often specific to particular
geographic regions and topics, the methodology which encourages positively-defined, analytical
analyses becomes universal. Properly structured question identification, sampling, experimentation,
data analysis, and documentation are all important components of a well executed, cost-effective
study. During emergency spill evaluation, this structured approach can prove invaluable in obtaining
the results necessary for immediate remediation. It is precise, well-documented methodology which
will also allow scientists to gain the information necessary to move forward in the battle to reduce
petroleum contamination. Evaluating and building upon past records of hydrocarbon release,
weathering and remediation can eliminate unnecessary errors, and expose insightful new avenues to
future study.
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Literature Cited:
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Other Stresses. 2nd Edition. San Diego: Academic Press, 1995.
(2) Swannell, R.P.J., K. Lee, and M. McDonagh. “Field Evaluations of Marine Oil Spill
Bioremediation.” Microbiological Reviews. 60.2 (1996): 342-365.
(3) Briggs, K.T., S.H. Yoshida, M.E. Gershwin. “The Influence of Petrochemicals and Stress on the
Immune Systems of Seabirds.” Regulatory Toxicology and Pharmacology. 23.2 (1996): 145-155.
(4) Parker, Sybil, ed. McGraw-Hill Encyclopedia of Chemistry. New York: McGraw-Hill, 1993.
(5) Douglas, G.S. et al. “Environmental Stability of Selected Petroleum Hydrocarbon Source and
Weathering Ratios.” Environmental Science and Technology. 30.7 (1996): 2332-2339.
(6) Krahn, Margaret, and John Stein. “Assessing Exposure of Marin Biota and Habitats to Petroleum
Compounds.” Analytical Chemistry. 1 March 1998: 186A-192A.
(7) Connell, Desley W. et. al. Basic Concepts of Environmental Chemistry. Boca Raton:
CRC Press, 1997.
(8) Ghaddar, N.K., and A.M. Nawwar. “High Pressure Water Jets for Oil Containment in Calm and
Wavy Water: A Parametric Study.” Water, Air and Soil Pollution. 73.1-4 (1994): 345-361.
(9) Prince, Roger. “Bioremediation of Marine Oil Spills.” Trends in Biotechnology. 15.5 (1997):
158-160.
(10) Sugai, S.F., J.F. Lindstrom, J.F. Braddock. “Environmental Influences on the Microbial
Degradation of Exxon Valdez Oil on the Shorelines of Prince William Sound, Alaska.”
Environmental Science and Technology. 31.5 (1997): 1564-1572.
(11) Korda, A., et. al. “Petroleum Hydrocarbon Bioremediation: Sampling and Analytical
Techniques, In Situ Treatments and Commercial Microorganisms Currently Used.” Applied
Microbiology and Biotechnology. 48.6 (1997): 677-686.
(12) Frey, Randall. “Award Winning Biocides are Lean, Mean, and Green.” Today’s
Chemist at Work. 7.6 June 1998: 34-38.
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