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Chapter 42 - Oil

Authors: Tonie E. Rocke.

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Each year, an average of 14 million gallons of oil from more than 10,000 accidental spills flow into fresh and saltwater environments in and around the United States. Most accidental oil spills occur when oil is transported by tankers or barges, but oil is also spilled during highway, rail, and pipeline transport, and by nontransportation-related facilities, such as refinery, bulk storage, and marine and land facilities (Fig. 42.1). Accidental releases, however, account for only a small percentage of all oil entering the environment; in heavily used urban estuaries, the total petroleum hydrocarbon contributions due to transportation activities may be 10 percent or less. Most oil is introduced to the environment by intentional discharges from normal transport and refining operations, industrial and municipal discharges, used lubricant and other waste oil disposal, urban runoff, river runoff, atmospheric deposition, and natural seeps. Oil-laden waste-water is often released into settling ponds and wetlands (Fig. 42.2). Discharges of oil field brines are a major source of the petroleum crude oil that enters estuaries in Texas.

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Birds that are exposed to spilled or waste petroleum can be affected both externally and internally. Oil contamination of feathers (Fig. 42.3) disrupts their normal structure and function, and it results in the loss of insulation for warmth and waterproofing. Oiled birds lose the ability to fly, and they frequently die from hypothermia, starvation, exhaustion, or drowning. Birds that are exposed to oil during their reproductive season can also transfer lethal doses of the contaminant to their eggs during incubation. Even small quantities of oil (5–20 microliters) externally applied to eggs can kill embryos. Birds can also ingest, inhale, or absorb oil when exposed to a spill or while preening contaminated plumage. The toxic effects of ingested oil vary, depending on the type of oil and on the species of birds affected. These effects include gastrointestinal irritation and hemorrhaging, anemia, reproductive impairment, depressed growth, and osmoregulatory dysfunction (Table 42.1). Polycyclic aromatic hydrocarbons (PAH) contribute to the toxicity of crude petroleum and refined petroleum products, but the amounts of PAH in petroleum products vary greatly.

Unfortunately, the effects of petroleum pollution can persist long after the visible spill is cleaned or dispersed. Petroleum persistence in the water column is usually less than 6 months, but it can be much longer (more than 10 years) in other components of the environment. Chronic losses may result when birds ingest oil in contaminated food items. For example, oil from the 1989 Exxon Valdez spill is still sequestered in bivalve communities within the areas of contamination and, thus, is still available to birds and other wildlife that feed on bivalves. Subtle effects on reproduction, such as decreased egg production, reduced fertility and hatchability, and decreased sperm production, as well as reduced immunologic function and impaired disease resistance, may occur as a result of ingesting oil-contaminated food (Table 42.1).

Figure 42.1
Click Illustration for full-page viewOrigin of petroleum spills, 1987-94.


Figure 42.2
Click Photo for full-page viewWastewater laden with petroleum being discharged into a settling pond.



Figure 42.3
Click Photo for full-page viewOiling disrupts normal feather structure and function.

Table 42.1 Commonly reported effects of oil toxicosis in birds.

Impact Consequences
Mechanical Loss of waterproofing and insulation value of feathers

Wetting, chilling, and hypothermia leading to death
Exhaustion due to depletion of body stores, inability to feed,
and greater expenditure of energy to maintain body heat and
stay afloat
Altered behavior

Toxicological Pathological changes in tissue

Inflammation of gastrointestinal lining

Physiologic disruptions

Altered endocrine function
Liver and kidney disorders
Altered blood chemistry
Blood disorders including anemia
Impaired salt (nasal) gland function resulting in disruption of

Reproductive Embryotoxicity
Impaired reproduction
Other Reduced growth and development
Reduced immunologic function
Impaired disease resistance

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Species Affected

A wide variety of birds and other wildlife have been affected by oil. The bird species affected depend on the location of the oil and the behavior of the birds. Species that suffer the greatest losses are gregarious, spend most of their time on the water, often near shipping lanes, and dive into the water to find food or to avoid disturbance. Seabirds, such as auks, guillemots, murres, puffins, sea ducks, and penguins, are particularly susceptible to contamination from oil spills (Fig. 42.4). In addition, annual losses of marine birds occur due to natural oil seeps along the Santa Barbara Channel of the California coast.

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Species with high reproductive rates may quickly recover from a spill, but for species with low reproductive rates, such as brown pelicans, oil pollution can cause catastrophic losses and it may take decades for populations to return to prespill numbers. Even oiled brown pelicans that have been successfully rehabilitated have reduced reproductive success.

Winter storms increase the likelihood of transport spills, making January, February, and March the peak spill season. This is also the time of year when seabirds and waterfowl congregate in wintering areas, resulting in an increased potential for significant bird losses.

Sea and bay ducks (scoters, scaups, oldsquaws, canvas-back) that tend to concentrate on wintering grounds and diving birds (grebes, loons, and mergansers) that overwinter in marine environments or on large water bodies with commercial shipping are quite vulnerable to oil pollution, especially during winter months. Eiders are vulnerable most of the year.

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Distribution and Extent of Mortality

The oiling of migratory birds is not limited to specific geographic areas. Accidental oil spills have occurred in all 50 States including inland waters, such as rivers and nonnavigable waters, and in open coastal waters, ports and harbors. Although it is not possible to accurately estimate the number of birds lost to oil pollution, in many cases the mortality has been substantial (Table 42.2). Bird losses of 5,000 or more are common for larger oil spills. Reports are usually of the numbers of oiled birds found dead or moribund on the shore, but these estimates may be inaccurate because of search biases, accessibility of the shore, losses of birds that have sunk to the bottom, and other factors. An important source of error in estimating losses in marine environments is the unknown proportion of oiled birds that die at sea but that do not reach the coast.

In addition to accidental spills, other opportunities for animal exposure to oil occur in association with oil production, petroleum refining, and highly industrialized locations throughout the United States. Persistent oil pollution is a chronic problem around marinas and ports due to discharges from shipping and boating activities and storage tank cleaning, but, unfortunately, the numbers of birds affected by oil pollution in these areas are unknown. In the Playa Lakes regions of eastern New Mexico, northwestern Texas, and western Oklahoma, open pits and tanks containing oil and oil-field wastes have been reported to claim the lives of approximately 100,000 birds each year (Fig. 42.5).

Figure 42.4
Click Illustration for full-page viewRelative susceptibility of birds to oiling.

Table 42.2 Examples of bird mortality from oil spills.

Vessel or source   Year Site Estimated bird mortalities
Exxon Valdez 1989 Prince William Sound, Alaska 350,000–390,000
Nestucca 1988 Grays Harbor, Washington 50,000
Amoco Cadiz 1978 Brittany, France 20,000
Barge STC-101 1976 Chesapeake Bay, Virginia 20,000–50,000
Torrey Canyon 1967 English Channel 30,000
Gerda Maersk 1955 Elbe River, Germany 500,000


Figure 42.5
Click Photo for full-page viewThese oiled birds were recovered from oil-field wastewater pits in the southwestern United States.


Figure 42.6
Click Photo for full-page viewOiled birds become wet and chilled because oil damages feather waterproofing and insulation properties.

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Field Signs

Major oil spills are frequently accompanied by intensive media coverage, and they may be well publicized before slicks or affected birds appear. However, small spills, especially those of unknown origin, often go unnoticed except for the appearance of a few contaminated birds. Oiled birds are frequently wet and chilled because the oil damages feather waterproofing and insulating properties (Fig. 42.6); birds may ride lower in the water than normal because they have lost feather buoyancy. Oiling is suggested when water birds leave the water for islands, rocks, pilings, and other surfaces because they are chilled (Fig. 42.7). Birds that survive for 48 hours or more after oiling are often thin, and even close to starvation, because they have stopped feeding and are using first body fat and then muscle tissue to produce heat in response to chilling.

Matting of the feathers occurs from external oiling. Oil can usually be seen or smelled on the feathers, but some light, transparent oils may be difficult to detect. One useful technique for detecting oiling is to place a few feathers from the bird in a pan of water and watch for an oil sheen to appear (Fig. 42.8). An enzyme-linked immunosorbent assay (ELISA), which detects PAH in oil, can provide quick confirmation of the presence of petroleum products on fur or feathers.

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Gross Lesions

Necropsy findings of birds that die from oil exposure are highly variable. Birds are often emaciated, and oil may be present in their trachea, lungs (Fig. 42.9), digestive tract, and around the vent. The lining of the intestine may be reddened, or the intestine may contain blood. The salt glands, which are located over the eyes, may appear swollen (Fig. 42.10), and the adrenal glands may be enlarged. A variety of other changes in the normal appearance of tissues and organs may also be present, but no specific or consistent lesion is typical in animals that are exposed to oil.

Figure 42.7
Click Photo for full-page viewCommon mure out of water due to oiling.


Figure 42.8
Click Photo for full-page viewIf external oiling is suspected, place feathers on water and watch for oil sheen.


Figure 42.9
Click Photo for full-page viewIn severe cases, oil may be inhaled and may discolor the lungs, such as in this Canada goose.


Figure 42.10
Click Photo for full-page viewSwollen salt glands.


Diagnosis of oiling is seldom a problem; visible oil on the bird or in the environment usually suffices (Fig. 42.11). However, proving that oil has caused mortality is more complex. For damage assessments and cause-of-death determinations, it must be determined that oiling did not occur after the death of the animals in question.

Chemical analyses of tissues or eggs are difficult to use for diagnosis because the chemical composition of petroleum products is complex. Therefore, good background information and field observations are an integral part of specimen submission to diagnostic laboratories (see Chapter 1, Recording and Submitting Specimen History Data). Submit whole carcasses whenever possible.

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Treatment of oil spills within the States, territorial possessions, and territorial waters of the United States is legislatively mandated by the Oil Pollution Act of 1990. The Act mandates the inclusion of a fish and wildlife response plan within the National Contingency Plan and the creation of Area Contingency Plans. These plans provide for an integrated response to a spill with assigned agency responsibilities for protecting fish and wildlife and environmental cleanup.

In the event of a spill, contact the National Response Center at the 24-hour, toll free number 1-(800)-424-8802. The National Response Center will advise the responsible agencies (Coast Guard, Environmental Protection Agency, and natural resource trustees) who will then respond to the event. In some States, notably California, State agencies may have lead responsibility for oil spills.

Cleaning oiled birds may not be justified on a "population" basis, but it is desired by the public, required by both State and Federal laws, and warranted when rare, threatened, or endangered species are involved. Contingency plans that were developed under the Oil Pollution Act address wildlife rehabilitation. Do not attempt to rehabilitate oiled animals without knowledge of cleaning techniques. For situations that do not require a response mandated by the Act, obtain advice from State wildlife resource agencies and the private sector (Table 42.3).

Scaring devices and other forms of disturbance can be used to discourage bird use of oil-polluted areas. If a polluted area is being used or is likely to be used by endangered species, it may be helpful to initiate actions that will attract the birds to other locations while the spill is contained and cleaned. All actions taken, including wildlife rehabilitation, should be in concert with those mandated to address oil spills.

Figure 42.11 Diagnosis of oiling is facilitated when oil is plainly visible on the carcass, such as this bald eagle (A), herring gull (B), and Canada goose (C).
Click Photo for full-page view(A) Click Photo for full-page view(B) Click Photo for full-page view(C)

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Human Health Considerations

Direct contact with petroleum, handling oiled wildlife, and activities associated with the cleanup are all potentially hazardous to humans. Health impacts due to the toxic effects of petroleum include contact dermatitis, increased skin cancer risk, eye irritation, and problems associated with inhaling volatile components of petroleum products. These products may be contaminated with other chemicals including polychlorinated biphenyls (PCBS) and organophosphates. Wear protective clothing to prevent direct exposure of oil to skin surfaces. Preventing injuries during spill containment and cleanup requires a cool head, advice from experts, and close supervision of workers — especially volunteers. Two major concerns are drowning and hypothermia.

Workers should not enter the water, climb slippery cliffs, or put themselves in hazardous situations to rescue birds. Also, the birds themselves present a hazard. Many sea birds have sharp, "spearing" beaks and often aim for the eyes of their predators — and their caretakers. Always wear goggles when handling these birds.

Table 42.3 Sources of information for rehabilitation of oiled birds.

Many individuals and groups have expertise in the rehabilitation of oiled birds and other
wildlife. The following are major programs that conduct this type of activity.
Program and address Telephone
Tri-State Bird Rescue and Research, Inc.
110 Possum Hollow Rd., Newark, DE 19711
California Department of Fish and Game
Office of Oil Spill Prevention and Response
Oiled Wildlife Care Network
Wildlife Health Center
University of California, Davis, CA 95616
International Bird Rescue Research Center
699 Potter St., Berkeley, CA 94710

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Supplementary Reading

  • Albers, P.H., 1995, Oil, biological communities and contingency
    planning, in Fink, L., and others, eds., Wildlife and oil spills:
    response, research, and contingency planning: Hanover, Pa.,
    The Sheridan Press, p. 1–10.
  • Albers, P.H., 1995, Petroleum and individual polycyclic aromatic
    hydrocarbons, in Hoffman, D.J., and other, eds., Handbook of
    Ecotoxicology: Boca Raton, Fla., Lewis Publishers, p. 330–355.
  • Bourne, W.R.P., 1976, Seabirds and pollution in Johnson, R., ed.,
    Marine Pollution: London, Academic Press, p. 403–502.
    Burger, A.E., 1993, Estimating the mortality of seabirds following
    oil spills: effects of spill volume. Marine Pollution Bulletin,
    v. 26, p. 140–143.
  • Flickinger, E.L., 1981, Wildlife mortality at petroleum pits in
    Texas: Journal of Wildlife Management, v. 45, p. 560–564.
  • Hoffman, D.J., 1990, Embryotoxicity and teratogenicity of
    environmental contaminants to bird eggs: Reviews of Environmental
    Contamination and Toxicology, v. 115, p. 39–89.

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