Petroleum is a mixture of hydrocarbons and their derivatives that occur naturally in the earth. Although liquid petroleum, more commonly known as crude oil, contains light or volatile hydrocarbons such as octane (C8H18), it also consists of gases, waxes (solid hydrocarbons), and bituminous materials such as asphalt and tar.

Petroleum, which is distributed liberally through the earth's crust, has been utilized as a heating and construction material since antiquity. For example, an asphalt ring dating from the Sumerians in 3500 B.C. has been excavated at the site of the prehistoric city of Ur in southern Babylonia.1

For the next 5450 years the earth's population exploited little of its oil reserves. However, in the last 50 years major world oil dependency has been prompted by the rapid rise of mass transportation and the emerging petrochemical industry after World War II. A flourishing world oil trade has evolved as a consequence of the uneven distribution of the world's oil reserves. While oil is pumped through extensive pipelines on land, several thousand oil tankers traverse the world's seas as components of an extensive petroleum transportation system. Although oil consumption relative to other energy sources has decreased modestly during the last decade, Figure 1 clearly shows that oil is still a dominant energy source.

Origin of Petroleum

Because it is derived from decaying plant and animal debris, primarily phyto- and zooplankton,a petroleum is referred to as a fossil fuel. While the water-insoluble organic components of these deposits initially contained oxygen, oxygen was largely removed by two processes. The elimination of water, or dehydration, was accomplished under conditions of high pressure from accumulating sediment, while decarboxylation, the evolution of carbon dioxide occured due to the action of anaerobic bacterial decomposition. Definitive evidence favoring theories that connect petroleum to organic rather than inorganic sources stems from the observation of optical activity among certain petroleum constituents. Plausible source materials for the porphyrinb constituents of crude oil are chlorophyllc and heme.d Additionally, fatty acidse are prime candidates as petroleum source materials because they can be readily converted to hydrocarbons by decarboxylation (equation (1)).

RCO₂H → RH + CO₂(g) (1)
fatty acid hydrocarbon
for example:
CH₃(CH₂)₁₅CH₂CO₂H → CH₃(CH₂)₁₅CH₃ + CO₂(g)
stearic acid heptadecane

Although oil originates in a sedimentary marine source bed, it ultimately migrates through faults and fractures created by tectonicf plate movement into reservoir rock. Reservoir rocks are usually sedimentary rocks such as sandstone or limestone whereas typical cap rocks, which prevent the escape of the volatile components of oil, are clays and shales that are far less permeable. Stratificationg into discrete gas (i.e., methane), oil, and water layers often occurs in the reservoir rock.

Composition of Petroleum

The proportion of oily constituents has been used as the key criterion in differentiating petroleum and asphalt. Petroleum is usually characterized as containing >50% oily constituents.

A complex mixture of substances, petroleum consists predominantly of hydrocarbons with metals and compounds containing nitrogen, sulfur, or oxygen present in minor quantities (Table 1). The hydrocarbon components of petroleum fall into three classes: paraffins or saturated hydrocarbons, either branched or unbranched (C_nH_2n+2), cycloparaffins or naphthenes (C_nH_2n where only one ring is present), and aromatics such as benzene (C₆H₆). The non-hydrocarbon components consist of either metals or sulfur-, oxygen-, or nitrogen-containing compounds.

Interconversion among the various hydrocarbon constituents of petroleum occurs via hydrogen addition or loss . It is probable that these chemical transformations occur during the formation and development of oil reserves, possibly due to the catalytic effect of cavities in porous clay.

Table 1. Hydrocarbon Constituents of Petroleum

Hydrocarbons	Examples
Paraffin
Naphthenes
Aromatics
Non-Hydrocarbons	Examples
Sulfur Compounds
Oxygen Compounds
Nitrogen Compounds
Metals	Fe, Ni, V, Cu

Properties of Petroleum

Due to their hydrophobic or nonpolar nature, hydrocarbons are not soluble in water. Because they are less dense than water, hydrocarbons float. Crude oil typically has a density of 0.85 g/mL.

Volatility is one of the fundamental characteristics of liquid fuels. As such, it forms the basis for the characterization of liquid petroleum fuels such as liquefied petroleum, gasoline, aviation fuel, naphthas, kerosene, gas oils, diesel fuels, and fuel oils.

Petroleum Refining

Separation of commercially important components of petroleum is achieved using a process known as fractional distillation. In fractional distillation, a vertical fractionating column with a large surface area is utilized to improve distillation efficiency. Commercial fractionating columns (Figure 2) consist of many horizontal plates that allow for repetitive vaporization-condensation cycles of the distillate so that the vapor reaching the top of the column is highly enriched in the more volatile components of the distilland. This fractionation is achieved by the establishment of a temperature gradient within the fractionating column; thus, the temperature at the top of the column is lower than is the temperature at the bottom of the column. Ideally, the temperature at the top of the column will correspond to the boiling point of the most volatile component of the original mixture.

Because hydrocarbons are essentially nonpolar in nature, separation of hydrocarbons occurs as a function of increasing molecular weight, which correlates with increasing boiling point (Table 2). For the series of petroleum constituents listed in Table 2, the order of emergence from a fractionating column parallels the boiling point: pentane, benzene, cyclohexane, octane, decalin, phenanthrene. Practically speaking, it would be difficult to separate completely benzene and cyclohexane due to the similarity in their boiling points. Fractional distillation of petroleum affords numerous fractions as a crude function of carbon number and boiling point (Table 3).

Table 2. Representative Examples of Petroleum Constituents

Name	Formula	MW (g mol-1)	BP (°C)
Butane	C4H10	58.13	-0.5
Pentane	C5H12	72.15	36
Benzene	C6H6	78.12	80
Cyclohexane	C6H12	84.16	81
Octane	C8H18	114.23	126
Decalin	C10H18	138.25	196
Phenanthrene	C14H10	178.24	340

Table 3. Approximate Composition and Boiling Points of Various Petroleum Hydrocarbon (HC) Fractions
Source: Reference 2, p 114.

Name of Fraction	Representative HCS	Approximate BP (°C)
Natural gas	CH4	-161
Liquefied gas (LP gas)	C3H8, C4H10	-44 to +1
Petroleum ether	C5H12, C6H14	30-60
Aviation gasoline	C5 to C9	32-150
Auto gasoline	C5 to C12	32-210
Naphtha	C7 to C12	100-200
Kerosene	C10 to C16	177-290
Fuel oil	C12 to C18	205-316
Lubricating oils	C15 to C24	250-400

Octane Rating

Gasoline is one of the commercially important fractions that result from petroleum refining. In the internal combustion engine of an automobile, energy is produced by the ignition of a compressed mixture of air and gasoline. The combustion of the gasoline creates gases, carbon dioxide and water vapor (equation (2)) , the pressure from which creates mechanical work by forcing a piston down a cylinder. Unbranched hydrocarbons such as octane have a great tendency to ignite spontaneously during this process. This phenomenon of pre-ignition is known as "knocking," which reduces power efficiency and increases engine wear.

C₈H₁₈ + (25/2) O₂ → 8 CO₂(g) + 9 H₂O(g) (2)
octane

Octane rating is a numerical scale that reflects the relative tendency of a gasoline component to cause engine knocking. On this scale heptane is assigned a rating of zero; 2,2,4-trimethylpentane (isooctane), 100. Because octane results in even more knocking that heptane, its rating is -19. Gasoline with an octane rating of 87 is equivalent in "knocking" potential to a mixture of 87% isooctane and 13% heptane.

Aromatics generally have higher octane ratings: benzene, 105; toluene, 120. However, concerns about the toxicity of the more volatile aromatic components of petroleum (BETX) - benzene, ethylbenzene, toluene (methylbenzene), and xylene (dimethylbenzene, which can exist as the ortho, meta, or para isomers) - has resulted in a modest relaxation of desirable octane rating. Octane ratings of 86-95 are frequently encountered at the gasoline pump. Octane ratings less than 100 ensure a minimal contribution from aromatic hydrocarbons.

Prior to 1970, tetraethyllead was routinely added to gasoline to increase its octane rating. Addition of 2.5 to 4.0 g of lead (3.9-6.2 g of tetraethyllead) per gallon of gasoline can raise 87 octane gasoline to 93 octane. However, the use of lead additives represented a health risk due to the presence of finely-divided particles of PbClBr in automobile exhaust. In 1968, it was estimated that more than 98% of lead emitted in the atmosphere originated from gasoline combustion.2 To compensate for the reduction in octane rating that would result by eliminating lead additives, automobile manufacturers lowered the compression ratios of automobile engines to permit the use of lower octane fuel.

The conversion to lead-free gasoline has also been dictated by the use of catalytic converters (which would be poisonedi by lead) on automobiles since 1975, mandated by the Clean Air Act of 1970, to reduce nitrogen oxide pollution. Nitrogen dioxide is produced as a byproduct of combustion. Photodissociation of NO₂ yields two reactive species: NO can recombine with O to reform NO₂ or O can combine with O₂ to form ozone (O₃). The primary function of the catalytic converter is to reduce nitrogen oxides in the form of NO to nitrogen (equation (3)). Catalytic converters have resulted in a 76% reduction in the emission of nitrogen oxides.3

2 NO + 2CO → N₂(g) + 2 CO₂(g) (3)

Methods of Petroleum Refining

Due to the importance of enhancing the gasoline fraction in petroleum refining, the chemical processing is designed to increase the composition of the C₅-C₁₀ hydrocarbons (Table 3) of higher octane number, which are typically branched paraffinic, naphthenic, or aromatic compounds. The more common chemical processes in petroleum refining include six categories: cracking, polymerization, alkylation, isomerization, catalytic reforming, and hydrocracking.

Cracking

Heating petroleum at high temperatures (>350°C) favors the breakdown of higher molecular weight components into smaller (lower molecular weight) fragments. For example, thermal cracking of dodecane (C₁₂H₂₆) yields hexane and 1-hexene (equation (4)), both of which are viable gasoline components. Although olefins (alkenes) such as 1-hexene are rarely found in unrefined petroleum, they are abundant in processed petroleum due to the cracking phenomenon.

heat + CH₃(CH₂)₁₀CH₃ → CH₃(CH₂)₄CH₃ + H₂C=CH(CH₂)₃CH₃ (4)
dodecane hexane 1-hexene

Catalytic cracking is essentially thermal decomposition of hydrocarbons in the presence of catalysts such as a crystalline aluminosilicates (zeolites) or molecular sieves. In petroleum refining, catalytic cracking has largely superseded thermal cracking because it produces gasoline richer in branched paraffins, cycloparaffins, and aromatics.

Polymerization

Petroleum constituents containing fewer than five carbon atoms can be converted to higher molecular weight hydrocarbons via acid-catalyzed polymerization. A true polymerization would involve the addition of a monomer, a low-molecular-weight unit, to itself in a repetitious fashion to yield a high molecular weight compound. The reaction here is not a true polymerization process in that it is terminated at either the dimer or the trimer. For example, methylpropene (isobutene), a monomer, can be dimerized to form 2,4,4-trimethyl-1-pentene (equation (5)), an eight-carbon hydrocarbon that would enhance the octane rating of gasoline due to its extensive branching.

(5)

Alkylation

Acid catalysts such as sulfuric acid or aluminum trichloride promote reaction of either a highly-branched paraffin such as isobutane or an aromatic compound with an olefin such as ethylene or propene. In equation (6), we observe that benzene can react with propene to yield isopropylbenzene (cumene).

(6)

Isomerization

The value of isomerization in petroleum refining is twofold: unbranched paraffins can be converted to isoparaffins, thus increasing the octane rating of the gasoline fraction; isoparaffins such as isobutane thus produced can also be alkylated to liquid hydrocarbons in the gasoline range.

Catalytic Reforming

In the process of catalytic reforming, paraffins can first be transformed into naphthenes and then to aromatic compounds. Equation (7) illustrates the catalyzed reformation of hexane to cyclohexane (equation (7a)) and then to benzene (equation (7b)). A typical reforming catalyst is molybdenum oxide.

Hydrocracking

The process of hydrocracking couples catalytic cracking with hydrogenation. The reactions are catalyzed by dual-function catalysts: zeolite catalysts for the cracking function and platinum, nickel, or tungsten oxide for the hydrogenation function. The hydrogenation reactions occur because hydrogen is generated as a by-product in the course of catalytic reforming. In the example cited in equation (7), a total of four equivalents of molecular hydrogen is produced. Thus, the olefins produced in catalytic cracking are reduced to corresponding paraffins (saturated hydrocarbons). Aromatics are also reduced under the conditions employed for hydrocracking. Hydrocracking of naphthalene, for example, yields benzene via the intermediacy of various alkylbenzenes (butylbenzene, ethylbenzene, toluene).

Background

In an attempt to reduce U.S. oil imports, a consortium of oil companies announced plans in 1969 to construct a pipeline from Alaska's North Slope to Valdez, an ice-free port on the southeastern coast of Alaska. Federal approval for the 800-mile Trans Alaska Pipeline System (TAPS) was obtained in 1973, and the first oil tanker shipment originated from Valdez on August 1, 1977. It has been estimated that 75 tankers visit Valdez every month. Currently, crude oil from Alaska's North Slope accounts for roughly 25% of total U.S. oil production. During the past 18 years approximately ten billion barrels (in excess of 400 billion gallons) of North Slope crude have been transported by TAPS to the Port of Valdez.

The Spill

Shortly after midnight on Friday, March 24, 1989, the Exxon Valdez, a three-year-old 987-foot tanker carrying 1.25 million barrels (50 million gallons) of North Slope crude, ran aground on Bligh Reef in Alaska's Prince William Sound. The Exxon Valdez left the Port of Valdez at 9:21 pm on March 23, 1989. After navigating the tanker through Valdez Narrows into Prince William Sound (PWS), the harbor pilot had transferred command back to Captain Hazelwood at approximately 11:30 pm. Due to floating ice from the Columbia Glacer, Hazelwood had received permission from the Coast Guard to divert from the Southbound (western) lane of the Traffic Separation Scheme to the Northbound (eastern) lane. Rather than opting to reduce speed and allow the vessel to navigate the ice flow, however, Hazelwood chose to enter the 0.9 mile gap between the edge of the ice and Bligh Reef at accelerating speed. This course, a more severe detour outside the Traffic Separation Scheme, allowed little tolerance for error. Before retiring to his cabin at 11:53 pm, Hazelwood turned navigation over to the Third Mate with a command to make a right turn (to avoid Bligh Reef) when the ship was abeam the Busby Island light. At 12:04 am, the Exxon Valdez shuddered as it grounded on Bligh Reef. However, the radio distress call to the Coast Guard was delayed until 12:27 am.⁵

As a result of the grounding, eight of the vessel's eleven cargo tanks were ruptured. The resulting oil spill of 258,000 barrels (10.8 million gallons), or 20% of the ship's cargo, was the 34th largest in the world at the time and the largest in U.S. waters. Successful off-loading of the remaining 1 million barrels of oil was completed on April 4. While the waters of PWS were relatively calm in the immediate aftermath of the spill, a severe storm that commenced the third day after the spill had the effect of driving the spilled oil toward the shoreline at the southwestern end of PWS. The data in Table 4 (see map, Figure 3) on the chronology of the oil spill illustrate the effect of the storm on the spread of the oil spill.

The Aftermath

While the Alyeska Pipeline Service Company, the consortium of seven major oil companies that operates TAPS and the Valdez terminal, was legally charged with the responsibility of oil spill cleanup, budget-tightening measures introduced in 1981 had resulted in a partial dismantling of the oil spill response team. Due to the delay in oil spill response caused by this curtailment of personnel, the first Alyeska barge, loaded with 50,000 pounds of boom (floating barrier used for containment) and skimmers, did not arrive at Bligh Reef until 2:30 pm, more than 14 hours after the accident. It has been estimated that most of the oil released from the Exxon Valdez into PWS had already escaped from the vessel by 5:30 pm the day of the spill.

Overseeing the cleanup operation spearheaded by Exxon Co. was the Coast Guard at the federal level and Alaska's Department of Environmental Conservation (DEC) at the state level. However, mounting a cleanup campaign from Houston, TX, caused unfortunate delays although mobilization of equipment was initiated as early as 4:00 am Alaska time on March 24, 1989. Frank Iarossi, a graduate of the U.S. Coast Guard Academy and president of Exxon Shipping, arrived in Valdez at 5:37 pm on March 24 to assume control of the cleanup operation despite the fact that Alyeska was charged with full responsibility for oil spill cleanup in the contingency plan.5 This outcome was consistent with federal law that makes the polluter responsible for the cleanup unless that organization has insufficient resources, in which case the U.S. government (the Coast Guard in the case of offshore spills) intervenes.⁶

Figure 3. Map of Prince William Sound (PWS) and the South-central Gulf of Alaska (GOA)
Source: Environ. Sci. Technol. 1991, 25, p 203.

Table 4. Path of the Exxon Valdez Oil Spill

Day #	Date	Oil Front (MI)	Farthest Reach
4	March 27, 1989	40	Block Island (PWS)
7	March 30, 1989	90	Montague Strait (PWS)
11	April 3, 1989	140	Kenai Peninsula (GOA)
19	April 11, 1989	250	Northern tip of Kodiak Island
40	May 2, 1989	350	Southern range of Kodiak Island
56	May 18, 1989	470	Alaskan Peninsula

A variety of oil spill response technologies are available, many of which were either tested on a small scale or utilized on a large scale in the Exxon Valdez oil spill. The cost of the cleanup, which was suspended during the fourth summer season in 1992 with Coast Guard approval, exceeded $2 billion, most of it assumed by Exxon. Assessment of the relative merits of a variety of oil spill cleanup methods, however, is complicated by the physical variables that affect oil cleanup: time, oil composition, location of spill, and weather. Because oil spreads rapidly once spilled, the longer a spill spreads, the more equipment is required for the cleanup. This factor was certainly critical to the extent and subsequent cost of the Exxon Valdez oil spill cleanup. Oil composition influences cleanup because higher viscosity oil is more difficult to recover due to its tendency to clog mechanical pumps. The effect of weather is twofold: rough seas facilitate the formation of an intractable oil-water emulsion known as "mousse" and adverse weather complicates the deployment and operation of cleanup equipment. Finally, an offshore oil spill, especially in a more remote location, exacerbates logistics problems related to equipment availability. As the U.S. Office of Technology Assessment (OTA) has concluded, "the speed of a response is critical and is dependent on rapid decision-making, logistics, and training." ⁶

Natural Processes

The extent of oil evaporation is a function of the oil composition, the area and thickness of the oil slick, the temperature, and wind speed. Distillation fractions representing approximately 20% of Prudhoe Bay (North Slope) crude oil are most likely to evaporate under environmental conditions. Less volatile (higher boiling) components might evaporate, but only in the absence of the competing processes of dispersion and biodegradation.

Using a sophisticated computer simulation program, the On-Scene Spill Model (OSSM), scientists at the National Oceanographic and Atmospheric Administration (NOAA) have attempted to account for the fate of oil spilled from the Exxon Valdez. Mass balance estimates generated from this model predict that 20% of the original spilled oil evaporated. Once evaporated, the petroleum hydrocarbons are rapidly oxidized to photolysisj products. The more toxic monoaromatic and naphthalenic components , with a half-life in air of ca. 1 day, were 99% degraded within one week. While dispersion, according to this model, accounted for as much as 23% of the spilled oil just two months after the spill, after three years less than 1% remained in the water column (except as biodegradation products) and 13% resided in subtidal sediments, mainly in the Gulf of Alaska. Although oil is less dense than water, the adsorption of oil onto suspended particulate matter creates the possibility that adhered oil can sink to the bottom. The remainder of the dispersed oil was subsequently beached or biodegraded in the water column.7 The fate of the spilled oil at three different junctures - the first week of the spill (March 1989), three months after (June 1989), and three years later (June 1992) - is summarized in Table 5.

Table 5. Fate of the Exxon-Valdez Oil
Source: Reference 7

Process	March 1989	June 1989	June 1992
Evaporation and photolysis	10%	18%	20%
Dispersion (water column)	4%	28%	38%
Floating	84%	0%	0%
Beached	0%	48%	34%
Skimmed	2%	6%	8%

Mechanical Containment

Oil spill containment and cleanup devices consist of booms and skimmers, a technology that has seen marginal improvement over the past two decades. Booms are long, tube-like barriers equipped with underwater skirts that act as floating fences to contain the oil spill so that skimmers can be employed to pump the surface oil-water mixture and separate the oil from the water. If efficient, mechanical methods offer a benign cleanup strategy. However, using the current technology, typically only 10% or less of oil from major oil spills has been recovered. The most recent advancement in this technology has been the design of large dual-purpose vessels developed in the Netherlands as hopper dredges to keep the port open and as skimming vessels to assist in oil cleanup.⁸

This technology was, in fact, employed in the cleanup of the Exxon Valdez oil spill. However, its sole use was recognized as woefully inadequate. Even if all the containment boom in the U.S. Navy inventory had been deployed to the spill within the first 12 hours, it would have been barely sufficient to encircle the spill. What is more incredulous is the fact that the U.S. Navy response was not even requested until more than one week after the Exxon Valdez accident. Recovery methods ultimately accounted for over 8% of the original oil spill according to the OSSM computer model.⁷

Chemical Dispersants

Dispersants are detergents that break up oil slicks into small droplets that disperse into the water column, where they are subjected to gradual biodegradation by natural processes, or that sink into bottom sediments. The surface-active agents (surfactants) stabilize the oil droplets by orienting in the oil-water interface with the hydrophobic (lipophilic) end of the surfactant molecule in the oil phase and the hydrophilic end in the water phase (Figure 4). Most chemical dispersant formulations also contain a solvent to reduce viscosity and to facilitate dispersal. The advantage of dispersants is that they can be spread rapidly over a large area and can reduce the amount of shoreline oil contamination.

Figure 4. Mechanism of Chemical Dispersion
A: Surfactant locates at oil-water interface.
B: Oil slick is readily dispersed into micelles or surfactant-stabilized droplets with minimal energy.
Source: Reference 9, p 29.

Biological Hazards

The use of chemical dispersants on an oil spill is controversial due to perceived toxicity problems. Depending on the crude oil source, 20-35% of a fresh oil spill can evaporate in the first day or so after the spill. However, when chemical dispersants are used to disperse oil into the water column, the hydrocarbons that preferentially dissolve are the slightly more water-soluble aromatic hydrocarbons, the toxicity of which we have mentioned previously. Benzene, for example, is a human carcinogen, and acute exposure can result in respiratory failure. Thus, more marine organisms could be affected by toxic components of dispersed oil in the water column.

While early dispersants were toxic to many marine organisms, those that are currently available are less toxic than the oil they disperse. Much of the unfavorable notoriety of chemical dispersants stems from their use at the 5-million-gallon Torrey Canyon oil spill in Cornwall, England, in 1967. Due to use of dispersants, the algae, limpet, barnacle, and mussel populations were devastated. In fact, the acute toxicity of the dispersants used was attributed to the alkylphenol surfactants and the aromatic hydrocarbons in the solvent. With the reduced toxicity of newer formulations, major harm should not occur to biological species in near-surface water (other than impairment of insulation capability of fur and feathers).⁹

Controversy Surrounding Chemical Dispersants. The effectiveness of chemical dispersants, which depends on sea conditions and application techniques as well as the chemical nature of both the dispersants and the oil, is now of more concern than dispersant toxicity. EPA had devised a contingency plan that would allow each state to decide if and when dispersants would be used. The state of Alaska had thus established three dispersant-use zones. While dispersant use was not recommended at all in a zone 3 area (a fragile ecosystem), EPA and the state of Alaska had given the Coast Guard on-scene coordinator (OSC) pre-approval to use dispersants in regions far from sensitive shorelines. designated zone 1 areas. Although Bligh Reef was designated a zone 3 area, within 24 hours of the spill the oil had begun to extend into the more open zone 1 waters of PWS. The request by Alyeska for a dispersant trial, sent at 8:00 am on March 25, was delayed by a faulty FAX machine at the Coast Guard station in Valdez. Approval for the dispersant trial by the Coast Guard OSC came at noon on March 26. At 4:00 pm on March 26, a plane loaded with 3700 gallons of dispersant took off from Valdez. Differences of opinion emerged about the efficacy of the trial; while Exxon's Iarossi viewed it as quite successful, the Coast Guard OSC equivocated due to the lack of wind and surface action. Harvard's Dr. James Butler of the National Academy of Sciences cautioned that "not using dispersants because the water is too calm is a fallacy."5 Finally, by 7:00 pm on Sunday, March 26, agreement was reached to use dispersant in zone 1. However, the amount of dispersant available in Alaska, 365 drums, would only have covered 10% of the oil spill. As Exxon began flying in dispersant from around the world and manufacturing more at two facilities, the spring blizzard that arrived early Monday morning with gale-force winds effectively halted dispersant use before it had begun.

Controlled Burning

Fresh oil, which still contains many volatile components, is readily ignited by incendiary bombs lowered from helicopters. Burning can, in principle, eliminate up to 90% of the oil, thus sparing marine life and beaches. However, combustion releases black sooty smoke that contains toxic gases, which might cause nausea, headaches, and respiratory problems. The U.S. OTA has determined that combustion products released into the atmosphere are not more hazardous than those released by evaporating oil.⁶

Before spilled oil can be subjected to a controlled burn, the oil must be cordoned off with fireproof boom. Although only 500 feet of fire boom was available in Alaska at the time of the spill, the arrival of an additional 2500 feet of fire boom by noon on Saturday, March 25, was sufficient to allow for a test burn. The test burn successfully burned off approximately 15,000 gallons of oil in less than one hour, leaving only a small pool of tarlike residue. As Exxon prepared to run four additional test burns, this effort was stymied by the requirement of a permit from DEC due to the smoke irritation experienced by residents of the nearby village of Tatilek. The delay was critical because as time passed the more flammable components of the oil were evaporating and the remaining oil was more inclined to develop into the water-oil emulsion or "mousse" that would resist burning. DEC opted not to provide the permit for additional controlled burns.5 In 1978, French farmers on the coast of Brittany effectively halted talk of igniting the wreck of the Amoco Cadiz because they feared that soot would ruin their crops. And in 1990, when the Mega Borg tanker caught fire fifty miles off the coast of Texas, the public virtually demanded that the fire be extinguished, which it was.

Just three weeks before the Exxon Valdez oil spill, oil spill cleanup was brought under the Occupational Safety and Health Administration (OSHA) regulations governing hazardous waste operations. Thus, cleanup workers, who wore protecting rubber suits and gloves, underwent a decontamination procedure at the end of each work day. Other than concerns about the volatile aromatic "BETX" components of oil mentioned earlier, the material safety data sheet (MSDS) for crude oil refers to polyaromatic hydrocarbons (PAHs), which are known to cause skin cancer. Proper water handling and protective clothing effectively eliminated any threat from PAHs.

Natural Removal

The natural elements of wind, rain, and snow gradually dislodge oil from beaches and disperse oil particles, which bacteria degrade over time. While this do nothing approach causes no further disruption of the ecosystem, it is a slow process, especially in sheltered areas. Recovery might not occur for 10-20 years.

The extent of surface oil coverage on the most exposed beaches of PWS decreased to around 20% of the initial level during the winter of 1989-1990. Natural action either dispersed oil back into the water column or forced it into subtidal sediments. Overall, the average removal of subsurface oil during the 1989-1990 storm season was estimated at 55%.⁷

Background biodegradation due to the presence of hydrocarbon-eating bacteria in the environment varied greatly depending on the location. The mean fractional loss during the first year resulting from natural biodegradation in intertidal sediments was 28% for surface oil and 12% for subsurface oil. Predictions from the OSSM model are that biodegradation either on the beaches or in the water column accounted for as much as 50% of the original spill.⁷

Water Washing

Cold water washing is performed at low pressure by pumping sea water through fire hose and applying it to oiled beaches at low tide to dislodge oil. Cold water deluge, a variation of this technique, involves pumping sea water to a perforated hose placed parallel to the waterline above an oiled area. In either method the water flushes oil to the waterline where the oil is trapped by boom and recovered by skimmers at high tide. This technique, which works best on fresh oil, is relatively harmless to the environment. But the mere presence of many cleanup workers leads to land surface disruption.

After beached oil has weathered, it becomes more intractable and tar-like. Thus, high-pressure steam cleaners were employed to blast weathered oil from rocky beaches. Although hot water dislodges weathered oil better than cold water, the water at temperatures as high as 140°F sterilizes the beaches, leaving them temporarily void of marine life. High pressure also has the effect of driving oil deeper into subsurface sediment.

Exxon had requested approval to use Corexit 9580 M2, a kerosene-based solvent, as a means of removing oil from rock surfaces. Although in trial applications Corexit did exhibit oil-dissolving capability, containment problems precluded widespread use of the chemical.

Physical Removal

Physical removal of oil from beaches either manually or using equipment such a bulldozers can be used effectively to remove oil that has weathered on beaches that is impervious to other methods of removal. However, excessive removal of beach sediments can cause serious erosion, as was the case after the Arrow grounding in Nova Scotia in 1970 that released 3 million gallons of oil, or habitat alteration, as occurred in the Ile Grande salt marsh in North Brittany, France, following the 68 million gallon oil spill of the Amoco Cadiz in 1978.¹⁰

Oiled beach sediment and solid wastes collected in PWS and the Gulf of Alaska were either incinerated or buried in an industrial landfill in Arlington, OR. Using the OSSM computer program, it has been estimated that 5.5% of the original oil spilled was recovered in this manner.⁷

Bioremediation

Bioremediation involves the application of fertilizer to enhance the rate of production of naturally-occurring bacteria that feed on oil. By the action of aerobic bacteria, hydrocarbons are completely degraded to carbon dioxide and water, a process called mineralization. This method uses bacteria that are already in the environment, although the long-term effects of artificial fertilizers on the environment are not known.

In May of 1989, Exxon conducted field tests of moderately oiled beaches with a liquid oleophilick fertilizer that adhered to the oil covered surfaces and a slow-release solid water-soluble fertilizer. After toxicological screening revealed the process to be safe and effective, EPA granted approval for a large-scale application of nutrients to Alaskan beaches. Inipol,l the liquid fertilizer applied to beaches, contains 2-butoxyethanol, which can be toxic to mammals.

During July-September 1989, about 70 miles of shoreline in PWS were treated with two kinds of nitrogen- and phosphorus-bearing fertilizers to boost indigenous bacterial populations. While the initial results were inclusive, the data has been under evaluation by Exxon scientists. Measuring changes over time in the oil composition relative to a stable, high-molecular-weight hydrocarbon present in the oil when spilled allows quantification of the rate and extent of oil biodegradation. While pristane and phytane have been used as non-degraded markers in analyses of other oil spills, these two hydrocarbons were rapidly biodegraded. Instead, hopane, a C30 pentacyclic hydrocarbon, was selected as an internal conserved standard. The most abundant hopane in Alaskan North Slope crude oil is resistant to biodegradation for years. Hydrocarbon/hopane ratios have suggested that the addition of fertilizers accelerated biodegradation over background rates by 3.7-5.2 times for a one-month period following fertilization. Component compositions are determined by gas chromatography-mass spectrometry (GC/MS), vide infra.¹¹

NOAA scientists have determined that beaches treated with hot water recover more slowly than those left untreated. Not only does hot water sterilize, but it drives oil from the more desolate beach areas where fewer organisms live to the subtidal zone occupied by clams and other crustaceans more sensitive to oil than the barnacles and mussels found on the more exposed intertidal areas. Subtidal invertebrates proved to be highly vulnerable to the oil spilled from the Amoco Cadiz tanker in 1978 off the coast of Brittany.¹⁰

The high pressure washes (at pressures up to 100 psi) can also cause shifting beach sediment that can suffocate clams and worms, impeding recolonization. The recovery of the ecosystem after the 68-million-gallon Amoco Cadiz oil spill suggests the best cleanup strategy might be to allow nature to run its own course. As NOAA chief scientist Sylvia A. Earle has said, "Sometimes the best, and ironically the most difficult, thing to do in the face of an ecological disaster is to do nothing."¹²

In contrast, the EPA believes that physical cleaning of the beaches by Exxon dispersed the oil such that the greater surface area of the exposed oil allowed for enhanced biodegradation., which was limited only to the availability of nitrogen and phosphorus nutrients. The application of nitrogen- and phosphorus-containing fertilizers (bioremediation), according to EPA, caused no adverse ecological effects. Musselsn suspended in floating cages just offshore from the treated beaches exhibited no bioaccumulation.¹³

Beach cleaning was also recommended by the Alaska Department of Fish and Game, whose agenda was to ensure a clean breeding site for seals and sea lions. Furthermore, the state officials contended that the oil had already suffocated most of the intertidal life.¹⁴

As the most studied oil spill to date and the largest such incident in U.S. waters, the Exxon Valdez oil spill was a major impetus to the Oil Pollution Act of 1990, which established a five-cent per barrel tax on oil to create a $1 billion per spill cleanup fund. Although oil spill accidents represent only 5% of the estimated 700 million gallons of oil entering the seas annually, they dispense a very concentrated dose of oil to the environment when they occur.

The American Petroleum Institute, in acknowledging the futility of dealing with a catastrophic tanker spill, has stated the following: "Further research into recovery technology can certainly help in this regard, but it is not considered likely that we can move to the point of guaranteeing containment and recovery at sea."15 Thus, the emphasis ought to be on oil spill prevention. Notable improvements have been made in the area of prevention as a result of the Exxon Valdez oil spill.

Ship Escort and Response Vessel System (SERVS)

SERVS is a more secure oil transport system that has been implemented by Alyeska at an annual cost of $50 million. This system provides tanker escort for the 60 miles to the ocean entrance to PWS by two vessels, one of which is a 210-foot ship equipped with oil skimmers, containment boom, oil dispersants, and oil storage tanks.¹⁶

Marine Spill Response Corporation (MSRC)

U.S. oil companies have created MSRC, which consists of five regional spill centers, any one of which could handle an oil spill of 200,000 barrels. Established at an initial cost of $900 million in 1991, the MSRC plans to spend between $30 and 35 million on research and development of oil spill cleanup technology over a five-year period. It expects to contribute $1 million to $4 million per year thereafter.⁹

Hull Design

If a normal tanker hull is ruptured, oil is released into the water because the oil pressure exceeds the water pressure. However, in hydrostatic loading the oil would not be released because seawater would exert greater pressure than the oil in the tanker. This differential pressure would result from the incomplete loading of the hull to allow for a compressible air space above the oil. Under the Oil Pollution Act of 1990 double-hulled tankers, which provide a protective space between the outside wall of the vessel and the inner wall of the oil storage tank, will be required by 2015 in all U.S. waters. However, double hulls offer only a partial solution. In a high-impact collision, such as occurred in the Exxon Valdez accident, the accumulation of hydrocarbons in the space between the hulls could increase the likelihood of explosion.¹⁴

Remote-Sensing Technology

In the event of a future oil spill, remote-sensing technology may be helpful in locating the thicker region of a slick. Ultraviolet (UV) devices can differentiate between oil and water because the aromatic compounds in oil absorb UV light. While aromatic compounds in oil containing conjugated ¹-bond systems absorb light in the UV range (200-380 nm), water still absorbs more UV radiation than does oil. Infrared (IR) systems can discern differences in sea-surface temperature due to the differences in the physical properties of oil and water. Oil thicker than several thousandths of an inch can sustain a detectable difference in temperature. However, temperatures drop at night with an attendant alteration of the image. A third innovative approach involves a laser fluorosensor. While the oil absorbs light in the UV range, it would fluorescem in the visible spectrum. The unique fluorescense spectrum of the oil would prevent any ambiguity with the spectra of algae or anything else floating on the water. In fact, based on the oil fluorescence spectrum , it is possible to differentiate between diesel fuel, crude oil, and bunker fuel.¹⁴

Gas Chromatography/Mass Spectroscopy

Chromatography is the separation of a multi-component mixture by distribution between two phases, one stationary and one moving. In GC, the stationary phase is a liquid and the moving phase is a gas (the carrier gas). The one limitation on use of GC is that the liquid to be analyzed must be sufficiently volatile that, when it is injected into the heated GC (up to temperatures of 300°C), the sample will vaporize so that it can mix with the carrier gas. As the sample moves into the column containing the stationary liquid phase, the components of the samples interact with the stationary phase to different extents. For the nonpolar components found in oil, the separation is controlled by the van der Waal (London) forces that influence the boiling point order. Hence, the GC elution order parallels the fractional distillation process (Tables 2,3).

In GC/MS as each individual component of the oil exits the separation column, it is ionized by the mass spectrometer. The MS detector converts the intensity of the charge to the relative concentration of each component, the pattern of which confirms the sample origin, thus providing a "hydrocarbon fingerprint." The identity of an unknown can be determined by matching the sample's mass spectrum with that of a known compound via computer-assisted mass spectral library searches and probability-based matches.¹⁰

High-Performance Liquid Chromatography (HPLC)

Compounds that are either thermally labile or nonvolatile are more amenable to analysis by non-thermal methods. In this case, HPLC is the method of choice. As in GC, the sample to be analyzed (analyte) is partitioned between a stationary and a moving (mobile) phase, which travels through a column. Whereas the mobile phase in GC is a gas, in HPLC it is a liquid. Because most HPLC instruments are equipped with UV detectors, HPLC is a sensitive method for the analysis of aromatic hydrocarbons, which absorb UV light (vide supra).

Components of oil induce mixed-function oxidase (MFO) activity in vertebrate animals. Bile metabolites are the products of MFO activity in the liver. HPLC analyses of fish bile have been conducted to detect PAH compounds. Using fluorescent detection, the light is tuned to one or two wavelengths characteristic of PAHs. The strength of the signal emitted correlates roughly with the general level of bile exposure.

If bile metabolites are detected, then analyses can be performed for MFO enzymes. John Stegeman, a biochemist at Woods Hole Oceanographic Institution, has developed a MFO assay based on cloned antibodies to particular MFO enzymes. His test for MFO was used extensively during the spill. Results of his tests revealed that MFO induction was higher in oiled prickleback fish samples than in the unoiled controls. However, the significance of this induction is not easily interpreted.

After the Exxon Valdez accident, sediment samples were collected from ten sites in PWS to determine the degree of oiling. Sixty sediments were analyzed for Prudhoe Bay crude oil (PBCO), the most abundant oil on the North Slope, using a rapid HPLC screening method with fluorescence detection. The predominant aromatic compounds in PBCO are one- to three-ring alkylated ACs. However, as crude oil weathers or degrades with time, the dominant components in the aromatic fraction are the naphthalenes, phenanthrenes, and dibenzothiophenes. Accordingly, the two fluorescence wavelengths selected for analysis of the post-spill sediment samples were the composite for naphthalenes/dibenzothiophenes (290/335 nm) and that for phenanthrenes (260/380 nm). The HPLC assay was preferentially chosen because GC/MS analyses are expensive and time-consuming. However, selected GC/MS analyses were performed for comparison with the HPLC screening method. Intertidal sediments from four heavily oiled sites in PWS that had been treated with high-pressure, hot-water washes exhibited HPLC patterns similar to that of weathered PBCO. In contrast, sediments from three unoiled sites in PWS produced HPLC chromatographic patterns that more closely approximate that of diesel fuel (Figure 6). GC/MS analyses confirmed that PBCO was a primary source of contamination in many of the sediments collected in PWS. GC/MS results from the sediment samples contaminated with diesel fuel, a common fuel for fishing and pleasure boats, are consistent only with a diesel fuel refined from a crude oil low in dibenzothiophenes, such as Cook Inlet crude.¹⁷

Mollusks, in particular, are good indicators of oil pollution because they collect hydrocarbons in their tissues. As a means of assessing the environmental impact of tanker traffic on PWS, NOAA has monitored sediments and mussel beds at eight locations along the tanker route since the Valdez terminal began operating in 1977. Moreover, a baseline study of the port itself began eight years before the terminal and ballast treatment plant opened. Operators of supertankers en route to Valdez fill the cargo tanks with sea water as ballast. At the terminal the tainted ballast water, containing about 1% residual oil from the cargo tanks, is processed at Alyeska's treatment plant by skimming machines, aerators, chemicals, and oil-metabolizing bacteria. After treatment the effluent is pumped into the deep waters of Port Valdez. Since the early 1980's hydrocarbons have been detected in the bottom sediments and in mollusks near the discharge pipe. Subsequently, hydrocarbons have also been found in the bile fluid of certain bottom fish.¹⁸

In general, hydrocarbons are not concentrated in the food chain. Yet more than a year after the spill, NOAA biologists have detected elevated concentrations of aromatic hydrocarbons in shellfish such as mussels and clams, suggesting continued uptake of oil from the environment. However, contamination at unsafe levels was only found in two locations, Windy Bay (905 ppb) and Kodiak Harbor (80 ppb), compared to a control site at the village of Angoon (0.02 ppb) outside the spill-impacted area.¹⁹

Oil that continues to contaminate mussel beds might be implicated in the failure of the Harlequin duck to breed every year since the oil spill -- Harlequins feed on mussels and clams in shallow waters. An alternative explanation, however, is human interference, which has been aptly described by a scientist working for the Alaska Department of Fish and Game: "Massive amounts of human disturbance to stream mouths and other Harlequin habitats included thousands of mandays of manual cleaning, mechanical tilling, hot-water treatment, Inipol, weir construction, agency and contractor visits, ship and boat traffic in bays and lagoons, and low-level overflights by fixed-wing aircraft and helicopters. Because Harlequin ducks are sensitive to disturbance, and high levels of disturbance can be correlated with poor reproductive performance, this is the alternative hypothesis of the cessation of Harlequin reproduction in the oil spill area of western Prince William Sound."¹⁸

In the immediate aftermath of the spill, an estimated 4000 sea otters died from hypothermia induced by the loss of insulation from oil-soaked fur, from emphysema caused by breathing toxic vapors, and from poisoning promoted by oil ingestion. Before the spill approximately 15% of the otters that died each year were mature animals of breeding age. From 1989 through 1991 this figure jumped to greater than 40% but then declined to 22% by 1992, a sign of recovery in the otter population.

More money was spent on rescuing and rehabilitating oiled sea otters than on any other species. One motivation for the rescue plan was to study the disaster's effect on the animals. Otters remain warm as a result of a high metabolic rate; sea lions and seals, on the other hand, have large fat stores for insulation. The proper grooming of a sea otter's fur also provides insulation from air trapped within the interlocking hairs. However, when rescued oiled otters are shampooed, the shampoo remove subaceous oils that made the fur healthy and destroys the insulating ability of the fur. As a consequence, the clean animals shiver uncontrollably in the cold water of holding tanks. To compensate, their metabolic rates rise even higher, some dangerously so. Despite these problems, 225 of the 357 otters saved from the spill zone survived. The nagging question is, would they have survived on their own, in that many of the otters at the treatment centers had been only lightly oiled? Clearly, the effects of captivity were very stressful for the otters. For this otter rescue effort, Exxon spent over $18 million, or $81,000 for each otter that was saved.¹⁸

Seabirds are especially susceptible to direct oiling. Estimates range from 10,000 to 100,000 seabirds that perished in the spill. The oil spill arrived just as the breeding guillemot (a small seabird) adults were gathering in "rafts" on the water before heading off to nesting sites. In colonies within the spill site, the populations have been reduced by 40-60% as compared with stable populations outside the spill area. There has also been a dramatic shift in nesting behavior with one severe consequence: an average delay in egg laying of 45 days. One explanation for this anomaly is that the decimation of the guillemot population has deprived them of mature breeding birds to provide proper breeding cues.²⁰

Prior to the Exxon Valdez spill in 1989, the bald eagle population in PWS had rebounded after the banning of DDT in 1972. While the official bald eagle mortality rate from the spill was 151, the majority of carcasses were probably not recovered. Of greater concern, however, was the long-term effect of oil on the surviving eagles and their reproductive potential. Eagles were feeding on oily carrion, and there was concern about bioaccumulation in such birds of prey. Although birds as a group metabolize and excrete crude oil components better than do fish, the heavier hydrocarbons do accumulate in the fat reserves of birds and in the lipid-rich material of eggs. Oiling of the egg shells can be fatal to eight-day-old eagle eggs, but 11-day-old embryos survived shell oiling, suggesting that liver enzymes were sufficiently active three days later in development to neutralize the hydrocarbons. Some scientists have attributed to temporary reduction in eagle reproduction in oiled areas of PWS to the oil spill itself. But the evidence suggests that most eagle reproduction failure during 1990 can be attributed to nest abandonment caused by the disruption of shoreline cleanup, staffed by over 11,000 cleanup workers in 1990.¹⁸

Measuring Toxicity

Bioassay tests have provided the principal basis for determining crude oil toxicity. In most of the tests mortality has been utilized as the index of toxicity, expressed as LC50 data (the lethal concentration yielding 50% mortality over a specified exposure time). The LC50 data reflect the sensitivity of various marine invertebrates and fish to the "BETX" aromatic hydrocarbons.10 Because LC50 values convey nothing about sublethal effects, however, they are imprecise measures of toxicity.

As a significant portion of the oil has settled into subtidal sediments, there is risk of chronic exposure to fish such as salmon and halibut. Exposure to hydrocarbons can be assessed by analyzing for the presence of the enzyme cytochrome P-450E that catalyzes reactions induced by hydrocarbons. Fish samples from oiled areas have shown markedly high levels of cytochrome P-450E than those from unoiled areas. Whether these results pose a serious threat to the organisms is more difficult to ascertain, but previous studies suggest that elevated levels of P-450E correspond to long-term chronic effects in fish.²¹ On the other hand, the data indicate little if any detectable aromatic hydrocarbons in salmon samples from PWS.

Fish and marine mammals metabolize most aromatic compounds (ACs) in their livers and then excrete the metabolites into the bile. GC/MS was used to identify AC metabolites (naphthols, phenanthrols, and dibenzothiophenols) in the hydrolyzed bile of a small sample of salmon and pollock caught in PWS several months after the oil spill. The metabolites, which were not found in control fish from unoiled areas, were identified by comparison to those from the hydrolyzed bile of a halibut injected with weathered PBCO. The three types of metabolites were found in abundance in the fish captured in PWS from 5-12 months after the spill. Because PBCO and other North Slope crude oils contain relatively high proportions of dibenzothiophenes as compared to other Alaskan (i.e., Cook Inlet crude) and continental U.S. crude oils, the identification of high concentrations of dibenzothiophenols in the bile of the pollock and salmon implicates the North Slope crude as the source of exposure.²² In subsequent tests performed by NOAA scientists, the levels of bile metabolites in a variety of fish such as pollock and sole diminished to background levels in 1990 and 1991. No sublethal changes or liver lesions were observed in the fish, nor was there any reproductive damage. Because pollock and sole are not bottom dwellers, the earlier high levels of metabolites were tentatively attributed to their diet, which consists of a buffet of smaller fish and crustaceans.¹⁸

Because oil is so prevalent in the earth's environment, most vertebrates have adapted to its presence by developing enzymes that degrade oil. Aliphatic hydrocarbons, similar in structure to fatty acids, are metabolized by initial conversion to fatty acids via biochemical oxidation. The toxic "BETX" aromatics, however, react readily with living cells, and the heavier PAH compounds persist in organisms for longer periods by resisting breakdown. While the liver works valiantly to detoxify these chemicals, at some critical threshold the agent can become cancer-causing. After coping with the initial horror of the severe scarring of the natural environment of PWS, concerns about cancer naturally surfaced among the people living in and near Valdez. While most scientists believe that the oil spill will not cause any significant elevation in cancer risk to the human population of PWS, the fears are nonetheless understandable in an era when any increase in quantifiable risk is frightening.

The Impact On Humans. Because many Native Alaskans subsist on wildlife, numerous studies were conducted by NOAA on species normally eaten by them. No hydrocarbon contamination was found in the meat or blubber of harbor seals and sea lions. However, mollusks, such as clams and mussels, had sufficient hydrocarbon contamination to warrant concern. PWS subsistence fishing areas that were obviously oiled were also closed.¹⁴

The PWS salmon harvest, which is dominated by the pink salmon, has not been adversely impacted by the spill. In 1990 and 1991, the commercial catch reached all-time records. Because many Alaskans rely heavily on commercial fishing for a livelihood, the strength of the salmon harvest in 1990 and 1991 helped to alleviate fears caused by the drastic curtailment of the 1989 fishing season due to the oil spill. Where commercial fishing was permitted in 1989, the Alaska DEC and the U.S. FDA closely monitored the harvest.

In 1989, local fisherman had been instrumental in using oil containment booms to cordon off three salmon hatcheries and two bays where herring spawn. Every commercial fishery in the path of the oil was affected. Exxon provided monetary compensation to local fishers for lost income. And many fishermen recovered some or all of their losses by leasing their boats and services during the cleanup effort.¹⁴

Cleanup Success

Within six days of the spill, Exxon initiated an extensive water quality sampling program in PWS. The intent of the program was to assess possible impacts on marine species by measuring hydrocarbon concentrations in PWS. Water samples were collected at 35 offshore locations from March through October, 1989. The results of 2300 samples are summarized in Figure 5, a graph of the average PAH concentrations in PWS. The highest PAH concentration was registered in three heavily oiled bays at a level less than 1 ppb, below the 10 ppb maximum concentration of petroleum aromatics allowable by the State of Alaska.¹⁹

An interesting anecdote reveals the resiliency of the marine environment. After off-loading of the remaining 1 million gallons of oil that had not spilled from the Exxon Valdez , the vessel was towed to Outside Bay on Naked Island in PWS. Exxon invited NOAA biologists to inspect the blossoming marine life in the cargo holds. The NOAA scientists observed an environment rich in zooplankton, marine worms, algae, bacterial mats, and jellyfish. They theorized that oil-eating bacteria from the nutrient-rich water of PWS had attracted larger predators such as fish, making the damaged hull a microcosm of the marine food chain.¹⁸

Figure 5. Average Polycyclic Aromatic Hydrocarbon (PAH) Concentrations for PWS Water
Source: Reference 19, p 27.

The answer depends on one's definition of recovery. The National Academy of Science rejects the notion of a "recovery to pre-spill conditions," an impossible event given the dynamic processes operating in the coastal milieu. Recovery will have occurred when the environment can support the same general range of life and biomass as before the spill.¹⁰ Using this definition, PWS has recovered. Virtually all species in PWS remain abundant and are successfully reproducing in the area impacted by the spill. The exception of the Harlequin duck has been discussed previously. And the sea lion population was already in serious decline prior to the oil spill.

According to the Exxon Valdez Oil Spill Trustees (the Alaska and federal representatives responsible for "restoring" the Sound after the determination and settlement of damages), "in a scientific sense, full ecological recovery has been achieved when the pre-spill flora and fauna are again present, healthy, and productive, and there is a full complement of age classes." By this more rigorous definition, the sea otter population has only partially recovered. Yet this conclusion has been challenged by other scientists who believe that PWS after the oil spill is still overpopulated by otters.¹⁸

The impact of the spill must ultimately be assessed against the backdrop of natural variation. A quote from a recently published Congressional Research Service report is revealing: "Despite short-term media attention to the catastrophic nature of major spill events, the chemicals contained in petroleum have long been part of the marine environment and physical impacts are likely to be temporary in the dynamic natural flux of the coastal environment."²³

References:

1. Speight, J.G. The Chemistry and Technology of Petroleum . Marcel Dekker: New York, 3, 1980.
2. Moore, J. W.; Moore, E.A. Environmental Chemistry. Academic Press: New York, 120-1, 1976.
3. The Ecosystem of Oil . American Petroleum Institute: Washington, DC, 1993.
4. Three Years After . Exxon Co.: Houston, TX, 1992.
5. Davidson, A. In the Wake of the Exxon Valdez. Sierra Club Books: San Francisco, pp 10-54,1990.
6. Coping With An Oiled Sea: An Analysis of Oil Spill Response Technologies . U.S. Congress, Office of Technology Assessment: Washington, D.C., 1990.
7. Wolfe, D.A., et al. Environ. Sci. Technol. , 28, 561A-568A, 1994.
8. Westermeyer, W.E. Environ. Sci. Technol. , 25, 196-200, 1991.
9. National Research Council. Using Oil Spill Dispersants on the Sea . National Academy Press: Washington, DC, 1989.
10. National Research Council. Oil in the Sea: Inputs, Fates, and Effects . National Academy Press: Washington, DC, 1985.
11. Bragg, J.R.; Prince, R.C.; Harner, E.J.; Atlas, R.M. Nature, , 368, 413-418, 1994.
12. "Exxon oil cleanup may have hurt ecology," Chemical & Engineering News ,11, April 15, 1991.
13. Pritchard, P.H.; Costa, C.F. Environ. Sci. Technol., 25, 372-379, 1991.
14. Holloway, M. "Soiled Shores," Scientific American, 102-116, October 1991.
15. Task Force Report on Oil Spills . American Petroleum Institute: Washington, DC, 1989.
16. Steiner, R.; Byers, K. Lessons of the Exxon Valdez . Alaska Sea Grant College Program: Fairbanks, Alaska, 1990.
17. Krahn, M. et al. Environ. Sci. Technol. , 27 , 699-708, 1993.
18. Wheelwright, J. Degrees of Disaster. Simon & Schuster: New York, 1994.
19. Maki, A.W. Environ. Sci. Technol., 25, 24-29, 1991.
20. Pain, S. "The two faces of the Exxon disaster," New Scientist, 11-13, 1993.
21. Kelso, D.D.; Kendziorek, M. Environ. Sci. Technol. , 25, 16-23, 1991.
22. Krahn, M. et al. Environ. Sci. Technol., 1992, 26 , 116-126, 1992.
23. Mielke, J. Oil in the Ocean: The Short and Long-Term Impacts of a Spill . Congressional Research Service, Library of Congress: Washington, DC, July 24, 1990.

Copyright © 2007 Claude Yoder. All rights reserved.
Site design by Karl Yoder