Introduction to Marine Oil Pollution by Bruce Currie-Alder

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Introduction to Marine OilPollutionOAD4: The fourth in a series of occasional papers examining theinteraction of oil development and deforestation in Latin America.

by Bruce Currie-AlderSubmitted to Tom Hutchinson in November, 1998.

Abstract:This paper is a background document intended to inform the debate as to whether coastal states have anobligation under international law to respond to events of marine oil pollution. Five themes are coveredincluding what is meant by petroleum, sources of marine oil pollution, behaviour of petroleum on openwater, ecological effects, and options for bioremediation of oil spills.

IntroductionThe year 1998 has been declared by the United Nations as the International Year of the Oceanand represents the highest expression of the increasing public awareness that there is reallyonly one large ocean. Extending around the world, circulating heat, moderating global climate,and providing livelihood and food for a significant amount of humanity, there is truly noreplacement for the ocean. Nor is any natural system so poorly understood and mistreated, thedeep ocean floor has been less explored than the surface of the moon and the ocean continues tobe a polluted by the waste from negligent human societies.

The most complex marine pollutant is petroleum and the precautionary principle signed at the1992 UNCED Conference in Rio de Janeiro, Brazil could be interpreted to imply that coastalstates have an obligation to respond to releases of petroleum at sea. This paper is intended as abackground document for any debate regarding the obligations of coastal states with regards tooil pollution, and is divided into five sections. The first section describes what is petroleum,while the second section names the sources of marine oil pollution. The third section describesthe behaviour of petroleum on open water, while the effects of oil pollution and options spillresponse are covered in sections four and five.

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1.0 What is Petroleum?

Petroleum is the remains of prehistoric biomass that has been buried in the earth and modifiedthrough exposure to tremendous heat and pressure over the geologic time scale. As such,petroleum literally is the product of ancient photosynthetic activity and should not beconsidered in anyway separate from the input of solar energy which represents nearly the totalenergy budget of the planet.

In its raw, in-the-ground form petroleum is called crude oil. Crude oil is a complex mixture ofhundreds of different hydrocarbons, which are long chains of carbon and hydrogen atoms,with some impurities which can include sulphur, oxygen, nitrogen and trace amounts of metalssuch as cadmium, calcium, copper, iron, nickel, sodium, uranium, and vanadium (Institute ofPetroleum 1963, p.157). In general, any particular crude oil can be expected to be composed of80% to 87% by weight carbon, 10% to 15% by weight hydrogen, 0% to 10% by weight sulphur,0% to 5% by weight oxygen, and 0% to 1% by weight nitrogen (Royal Society 1980, p.10).

The exact composition of crude oil varies greatly with respect to the unique geologic history ofthe landscapes in which they are found. An analysis of crude oil chemistry can fingerprint theorigin of any particular oil to a specific geographic region and crude oils are often traded undersuch names as West Texas Sour and Arab Heavy (see table 1).

Table 1: List of commonly traded world crudes and examples of prices, bbl=barrel of

crude (Oilweek 1995 and 1997).

World Crude$US/bbl12/18/95

$US/bbl11/26/97

Alaska North Slope @ West Coast 23.41 17.34

Arab Heavy 20.88 14.61

Arab Light 22.33 16.45

Brent @ London, UK 23.44 18.86

Dubai @ London, UK 21.32 17.93

Minas - Indonesia 23.22 18.84

Urals - Soviet @ London, UK 22.88 18.89

West Texas Intermediate @ Cushing 25.13 19.30

West Texas Sour @ Midland 23.62 17.65

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The hydrocarbons in crude oil all have more than four carbon atoms and are divided into threeclasses: aliphatics (alkanes and cycloalkanes), aromatics (those with benzene structures), andresins (polar hetrocyclic aromatic molecules containing nitrogen, oxygen, or sulphur) (see figure1). Crude oil in itself is not very useful, but can evolve a series of valuable products whendivided into hydrocarbons fractions of relatively uniform weight and chemistry. The process ofseparating crude oil is called refining and is accomplished by heating crude oil at the bottom ofa distillation tower, uniform hydrocarbon fractions then condense at differing heights insidethe tower and are drawn off for further processing.

Products evolved from refining can include asphalts, lubricants, plastics, paint ingredients,heating fuels, and motive fuels. The use of these products gives rise to a tremendous variety ofpetroleum hydrocarbons, ranging from simply alkane chains to complex polycyclic aromatichydrocarbons (PAHs) created by incomplete combustion, which one way or another arereleased into the environment.

Crude oil, with rare exceptions, is always less dense than water. Since lighter crudes often havefewer impurities and are more readily refined than heavy crudes, lighter crude oils areconsidered to be of higher quality and tend to command a higher price on world markets.Crude oil quality is measured in two ways: specific weight and grades API. Specific weight isdefined as the ratio of the weight of a litre of crude to an equal volume of water at anequivalent temperature (60 F or 15.6·C) and may be expressed as follows:

weight of one litre of crude

Specific Weight = ---------------------------------------- weight of one litre of water

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A far more commonly used measure of crude oil quality is the American Petroleum Institute(API) scale. The API scale is expressed in grades while specific weight is a unitless value.Grades API are related to specific weight by the following equation:

141.5

Grades API = ----------------------- - 131.5

specific weight

(Institute of Petroleum 1963, p.160)

Crude oils of greater than 45 grades API (specific weight less than 0.88) are considered light,while crude oils of less than 20 grades API (specific weight greater than 0.93) are consideredheavy (Hyne 1984, p. 132). After half a century of intense worldwide oil extraction, most easilyaccessible sources of light crudes have been economically exhausted and the medium crudes,with a density between these two extremes, is the most commonly traded crude oil.Additionally, previously uneconomical heavy crudes are being increasingly exploited due tocontinued demand for petroleum products and new refining technologies.

Market demand and supplies of crude oil are not uniformly distributed worldwide. Petroleumdemand is concentrated in the developed countries of North America and Europe which, whilecontinuing to exploit local deposits of crude oil, have become increasingly reliant on depositsfrom developing countries including Saudi Arabia, Nigeria, Venezuela, and Mexico. It isinteresting to note that apart from the Pretoria-Johannesburg urban centre, the lights ofNigerian coastal refineries are the brightest spot in Africa at night (NASA 1998).

This geographic separation between sources of supply and demand has given rise to asubstantial amount of sea-borne transportation of crude oil in tanker ships and, to a lesserextent, in pipelines. Volumes of crude oil are often measured in number of barrels with astandard barrel accepted to be equivalent to 42 imperial gallons (159.1 litres), and possessing anaverage energy content of 6,120,000 kiloJoules (Kraushaar and Ristinen 1993).

2.0 Sources of Marine Oil Pollution

According to a United Kingdom Royal Society report (1980, p. 18) estimating inputs for 1978,humanity’s exploitation of petroleum products does significantly increase the annual input ofpetroleum hydrocarbons into the ocean. Although the Royal Society report is dated, there is noreason to suppose the ratio of oil inputs has changed although petroleum use has increaseddramatically over the past twenty years.

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Terrestrial run-off and outfall from sewer systems, combined with natural petroleum seeps,were estimated to release for 3.45 million metric tonnes worldwide, or 70% of total petroleuminput into the ocean. Apart from highly polluted river deltas contaminated from sourcesupstream, there is little evidence that these releases have a significant impact on ocean ecology.Furthermore, these releases are relatively non-point source and thus result in extensive, lowconcentration distribution of petroleum which appears to be within the tolerance of manyocean communities. Mitigation of these releases depends on tighter policy controls on outfallwater quality, incentives and technology for recirculation of petroleum products withinindustry, and more efficient use of petroleum products including strict standards on motorvehicle operation.

The remaining 30% of petroleum input into the ocean is a combination of releases from marinetransport, offshore oil platforms, and coastal oil refineries. As point sources for petroleumrelease, these sources result in small area, high concentrations of petroleum hydrocarbons.While such releases are the most significant in terms of ecological damage, they also present thegreatest opportunity for intervention resulting in a strategic role for coastal states in themitigation of impacts on ocean ecology.

3.0 Petroleum Behaviour on Open Water

Despite humanity’s century long dependency on petroleum, marine oil pollution has only beenintensely researched since 1967 after the Torrey Canyon supertanker ran around off the Englishcoast releasing 177 000 tonnes of crude oil. The Torrey Canyon, along with such wrecks as theAmoco Cadiz, Exxon Valdez, and the blowout of Ixtoc 1 platform in Mexico raised publicawareness of the ecological risks of marine transport and increased the demand for newresearch and policy regarding marine oil pollution (Freedman 1995).

Open water oil spills have been documented to behave in predictable manner according to thephysical and chemical properties of the spilled material and the physical conditions of the sea(Freedman 1995, Royal Society 1980) (see figure 2). Since oil is less dense than water, any spillwill invariably start spreading across the surface of the water.This process is temperaturedependent as petroleum becomes more viscous at lower temperatures and spreads moreslowly, however without intervention, the spreading will ideally continue until the spill is auniform layer one molecule thick over the surface of the water. Studies performed by BarringerResearch Limited (1993) found the typical thickness of a heavy crude oil spill to be 0.02 mm intemperate open water, 0.2 mm thick in arctic open water, and 1.0 mm thick when washed ontotemperate shorelines. This matched well with Barringer’s previous experiments which foundone cubic metre of crude oil would cover 3500 cubic metres of tropical open water and 35 cubicmetres of arctic open water (1993). Therefore, we can surmise that for any particular oil spill the

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amount of open water covered by the spill will be ten times greater in tropical open water thantemperate open water, and a hundred times greater in temperate open water than in arctic.

Lighter fractions of petroleum volatilize and are carried away by wind, thus reducing thevolume of the spill. As might be expected, evaporation is more significant for spills of lighterweight petroleum products than for spills of heavier products. In a comparison study of crudeoil spills two days after release, Fingas (1993) found that 75% of the volume of a spill of lightcrude had disappeared due to volatilization while only 10% of the volume of a heavy crudespill was lost in this way. This increases the average density of the remaining material whichmay be broken down somewhat by sunlight and through oxidation from atmospheric oxygen.Meanwhile, wind and wave action affect on a spill in a variety of ways, not least of which istransport of the spill as it drifts across the ocean with the speed and direction of ocean currents(Royal Society 1980).

Soluble fractions of the material will be distributed into the water column under the spill and toa limited extent even insoluble fractions will be mixed into the water column. Some compoundsmay come into contact with ocean floor sediments and settle onto the surface of sedimentparticles. Along heavily contaminated coasts this results in a gradient where sediments foundin deeper water will contain only lighter petroleum hydrocarbons while sediments in moreshallow water will contain petroleum hydrocarbons of a variety of weights (Levy et al. 1988).

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Wind and wave action may also create oil-in-water emulsions, commonly known as "mousse"due to its cream sponge-like texture, and semi-solid spheres of heavier hydrocarbons known as"tar- balls". In these forms, oil becomes more resistant to further weathering and microbialaction. While water-in-oil emulsions continue to drift with ocean currents, tar-balls maybecome more dense than water and sink through the water column to the ocean floor.

4.0 Ecological Effects of Oil

The biological activity of the ocean naturally generates a variety of 8-carbon to 20-carbon alkylchains, or aliphatic hydrocarbons. We might, therefore, assume that these compounds do notpresent any significant threat to ocean life (Royal Society 1980). Some argument exists in theliterature as to whether lighter or heavier fraction of petroleum are of greater toxicity(Freedman 1993, Foght and Westlake 1992), but it seems clear that such generalizations are oflittle help from a practical perspective. Instead, just as crude oil is a complex mixture, it isnecessary to appreciate that oil can cause a complex variety of toxic consequences.

Depending on the compound involved, oil may act as a chemical or physical toxin. Examples ofboth forms of toxin are well documented in shore birds which come into contact with an oilspill. Oil adheres to the birds’ feathers reducing their insulation and comprising the waterproofbarrier of the feathers. These physical interactions reduce the birds buoyancy and ability toresist cold resulting in deaths from drowning and exposure. Where birds survive initial contactwith the spill, they may accidentally ingest amounts of oil while trying to clean themselves,which can lead to kidney, liver, and intestinal damage (Royal Society 1980).

Little research appears to have been done with regards to open water ecological effects of oilspills in temperate and tropical climates, but we may suspect that fish and aquatic mammalsare able to avoid such spills through diving and moving laterally away from moving spills.Since sound travels at different rates in oil and water, it is possible that aquatic organismscapable of echolocation are able to detect and avoid spills on the surface.

The weathering of oil by physical forces is termed biodegradation. Traditionally, clean-upefforts have followed physical forces to isolate and remove spills on open water. Such methodshave included the placement of floating booms around spills, the use of skimmer boats tocollect oil from the surface, and in-situ burning ignited either through dropping incinerarydevices onto the spill, or more recently through the of lasers (Fingas and Brown 1995, Chardiaeand Pelly 1994). These methods are described in other literature and it is sufficient to merelymention them here. A word of caution againstin-situ burning has been voiced by Brenner et al.(1991) however, who found that total PAH content in exhaust fumes from combustion was tento twenty times greater than the total PAH content of the spilled crude oil. While burning

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reduces a local problem, the total amount of potentially carcinogenic material in theenvironment is increased and spread over a greater distance.

5.0 Bioremediation

While biodegradation has a significant effect on oil spills in temperate waters, the best-knownmechanism for natural remediation in temperate climates is the mineralization of hydrocarbonsby aerobic bacteria into carbon dioxide and water according to the following formula(Matthews 1993):

bacteria

C6H5-CH3 + 9 O2 ------------------> 7 CO2 + 4 H2O + energy (or biomass)

This aerobic process is just one of many possible mechanisms of bioremediation which is theuse bacteria, fungi, and yeasts to mineralize complex hydrocarbons into simple constituentmolecules. Bioremediation processes may be aerobic or anaerobic. Anaerobic processes havebeen demonstrated to be important in the bioremediation of sediments (Coates et al.1997,Rueter et al. 1990) but, as we are primarily concerned in this paper with surface oil spills opento the air, our primary interest in aerobic bioremediation.

There is no single approach to bioremediation and it seems clear that the choice of methodsused must be in accordance to local conditions and available materials. While once promised asa "magic-bullet" approach to remediation of oil spills everywhere, the introduction of foreign orengineered micro-organisms and specially tailored chemical inputs to encourage their rapidgrowth on spilled oil has numerous defects. Such processes are often capital intensive and thereare no guarantees against the introduced species having a negative effect on local microbialpopulations or remaining in the ecosystem after spill clean-up.

A much more practical approach to bioremediation is the use of micro-organisms native to theeffected ecosystem. Bioenhancement is the addition of dispersants and/or nutrients to increasethe rate of aerobic degradation. While dispersants increase the surface area of oil available tomicrobial action by encouraging greater spreading of the spill, they should be used cautiouslyas there is increasing evidence that some dispersents may be more toxic than the oil they areused on. The addition of forms of nitrogen and phosphorus that are soluble in oil, however, canremove the most limiting factor to microbial growth and can effectively increase the rate ofbioremediation (Hoff 1992).

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Most bacterial species appear capable of mineralizing only a single compound in anyhydrocarbon mixture. An important exception to this specificity is the genus Pseudomonas, awidely distributed soil and water bacteria, which has been found to degrade a variety ofhydrocarbon compounds at both temperate and cold temperatures (Whyte et al. 1997, 1996,Ridgeway et al. 1990, Foght and Westlake 1988). Despite Pseudomonas’s ability, however,bioremediation methods that use a collection of microbial species are more effective thatreliance of any single species. Even when conditions are optimal, bioremediation can never beexpected to ensure 100% clean-up and such plans must expect there will be some petroleumresidue to be managed after bioremediation.

Where previous studies have already identified native micro-organisms that act upon oil, thesemicro-organisms can be isolated in the lab and added to the affected ecosystem. This process istermed bioaugmentation. During field work conducted in the Amazon in 1996, I have seen anextreme example of bioaugmentation where an Ecuadorean biologist had isolated nativebacteria after several small oil spills, grown colonies of species, and kept chilled coloniesavailable at all times for use in emergency response to oil spills.

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While bioremediation can be quite cost-effective, its use is somewhat limited on open water dueto the mixing and dilution from wave action. In near coast spills, booms may be erected tocontain a spill and nutrients and microorganisms added to work upon the oil. The spill may betreated in-situ or towed to a sheltered harbour for prolonged bioremediation. The developmentof a floating, solar-powered aerator may further increase the rate of bioremediation andwarrants research (see figure 3).

Conclusion

Petroleum is a complex mixture of hydrocarbons containing significant amount of impurities.Numerous compounds within petroleum may act as either physical or chemical toxins, thoughthe full impact of petroleum releases on open water have yet to be determined. A variety ofphysical, chemical, and biological methods exist for oil clean-up at sea. The methods used inany operation must be selected in accordance to local conditions and no minimum standard ofattention is immediately obvious. While physical oil collection has been traditionally used inclean-up operations, bioremediation methods which exploit naturally occurring micro-organisms possess great potential.

While emergency response to marine oil pollution is unlikely to become an international normin the short-term, efforts should be made to share mitigation strategies and technologiesbetween coastal states. Over the long-term, solutions to marine oil pollution must also includeconcrete policies on the part of major petroleum consumer states to reduce oil runoff into theocean which remains the most significant input.

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References Cited

Barringer Research Limited. 1993. Monitoring of plankton productivity, salmon migration, and oilpollution using a newly-developed airborne fluorescent sensor. (Report of research performedfor Environment Canada: Ottawa, ON)

Brenner, B.A. et al. 1991. Emissions of polycyclic aromatic hydrocarbons from the combustion of crudeoil on water. Spill technology newsletter 16. (Environmental Protection Publications,Environment Canada: Ottawa, ON)

Coates, J.D. et al. 1997. Anaerobic degradation of polycyclic aromatic hydrocarbons and alkanes inpetroleum-contaminated marine harbor sediments. Appl. Environ. Microbiol. 63(9): 3589-3593.

Fingas, M. And C. Brown. 1995. Review of remote sensing for oil spills. Spill technology newsletter 20(1-4). (Environmental Protection Publications, Environment Canada: Ottawa, ON)

Foght, J.M., P.M. Fedorak, and D.W.S. Westlake. 1990. Mineralization of [14C]hexadecane and[14C]phenanthrane in crude oil: specificity among bacterial isolates. Can. J. Microbiol. 36: 169-175.

Foght, J.M. and D.W.S. Westlake. 1992. "Bioremediation of oil spills". Spill technology newsletter 17(3).(Environmental Protection Publications, Environment Canada: Ottawa, ON)

Foght, J.M. and D.W.S. Westlake. 1988. Degradation of polycyclic aromatic hydrocarbons and aromaticheterocycles by a Pseudomonas species. Can. J. Microbiol. 34: 1135-1141.

Freedman, B. 1995. Environmental ecology: the ecological effects of pollution, disturbance, and otherstresses. (Academic Press: Toronto, ON).

Hyne, N.J. 1984. Geology for petroleum exploration. drilling, and production. (McGraw-Hill BookCompany: New York).

Kanaly, R. et al. 1997. Biodegradation of [14C]benzo[a]pyrene added in crude oil to uncontaminated soil.Appl. Environ. Microbiol. 63(11): 4511-4515.

Kraushaar, J.J. and R.A. Ristnen. 1993. Energy and problems of a technical society. (John Wiley & Sons,Inc.: Toronto, ON).

Hoff, R. 1992. Bioremediation: a countermeasure for marine oil spills. Spill technology newsletter 17(1).(Environmental Protection Publications, Environment Canada: Ottawa, ON)

Institute of Petroleum. 1963. Modern petroleum technology. (Editorial Reverte, SA: Mexico, DF).

Levy, M. et al. 1988. The distribution of petroleum residues in near-shore sediments from AtlanticCanada. Canadian Technical Report, Fisheries and Aquatic Sciences No. 1612. (Ministry ofSupply and Service Canada: Ottawa, ON).

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Matthews, J.E. 1993. Handbook of bioremediation. (CRC Press, Lewis Publishers: Ann Arbor, MI).

National Aeronautics and Space Administration. 1998. Earth from Space: Satellite Imagery Database.http://earth.jsc.nasa.gov/

Ridgeway, H.F. et al. 1990. Identification and catabolic activity of well-derived gasoline degradingbacteria from a contaminated aquifer. Appl. Environ. Microbiol. 56(11): 3565- 3575.

The Royal Society. 1980. The effects of oil pollution: some research needs. (The Royal Society: London,UK).

Rueter, P. et al. 1994. Anaerobic oxidation of hydrocarbons in crude oil by new types of sulphate-reducing bacteria. Nature 372(1): 455.

Whyte, L.G., L. Bourbonnière, and C.W. Greer. 1997. Biodegradation of petroleum hydrocarbons bypsychotrophic Psuedomonas strains possessing both alkane (alk) and naphthalene (nah) catabolicpathways. Appl. Environ. Microbiol. 63(9): 3719-3723.

Whyte, L.G., C.W. Greer, and W.E. Inniss. 1996. Assessment of the biodegradation potential ofpsychotrophic microorganisms. Can. J. Microbiol. 42:99-106.

Bruce Currie-Alder communicate with me at: BRUCE@ncf.ca