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Oil intoxication is the term used to describe the adverse effects of accidental exposure of wildlife to oil contamination. Oil exposure and intoxication generally occurs in heavily trafficked waterways as a result of oil tanker spills but has been reported from residential and business areas due to fuel oil or gasoline spills.
Aquatic bird populations are most commonly affected by accidental oiling and subsequent contamination of their eggs and young. The most obvious effect of oil contact is external feather oiling, which causes loss of buoyancy and loss of feather insulating properties resulting in death due to drowning or exposure. Ingestion of oil while preening results in many internal pathological changes. When birds return to their nests the eggs are contaminated by oiled feathers or feet resulting in decreased hatchability and increased embryonic mortality. Fish, shellfish, and marine mammals may be affected by accidental oiling as well.
Clinical Signs and Pathology
Externally oiled birds are obvious at first sight and exhibit varying degrees of exposure and intoxication. The highest mortality rates are seen in heavily oiled birds which have oil penetration through the outer feathers and down. Oil disrupts the structure of the feathers, compromising the waterproofing and insulating feathers of the plumage. Oil intoxication due to ingestion during preening results in aspiration pneumonia, gastroenteritis with bright green diarrhea, splenic atrophy (decrease in size), and liver hypertrophy (enlargement) due to fatty infiltration. Ulceration and hemorrhaging in the lining of the gastrointestinal tract may occur. Ulcerations of the corneal surfaces of the eyes and the lining of the mouth may also occur. Severe and fatal kidney damage may occur due to toxic effects of the oil on the kidneys and as a result of severe dehydration.
Oil inhibits ion and water uptake by the intestine, resulting in death due to dehydration. The acute gastroenteritis which is often present can be severe enough to result in anemia due to intestinal blood loss. Birds which survive heavy oiling may be reproductively impaired and either stop laying entirely or lay fewer eggs. Oil ingestion appears to weaken birds and may contribute to increased mortality during periods of stress. The effects of oil on young birds are growth retardation and delayed feather development. Eggs are most sensitive to oil exposure during the first ten days of incubation and oiling results in decreased hatchability, increased embryonic mortality and decreased hatching weight of surviving embryos. The decreased hatchability appears to be due to the toxic properties of oil, rather than a blockage of normal gas exchange. The decreased embryonic weights and fetal abnormalities are due to high concentrations of vanadium, nickel, mercury, and other heavy metals found as contaminants in crude oil.
Diagnosis can usually be made by the external appearance of the bird combined with the evidence at necropsy of pneumonia, fatty liver, and gastroenteritis. Definitive diagnosis can be made by laboratory analysis for the presence of petroleum hydrocarbons in fat, liver, and kidney tissue.
Treatment and Control
When feasible, treatment of oiled birds can be accomplished by immediate collection, stabilization, and cleaning of the plumage. Mucosal membranes are cleaned by removing oil from the mouth and nares with cotton swabs and flushing the eyes with warm sterile saline or ophthalmic irrigation solution. Depending on the condition of the animal, warm gavages of electrolyte solution and an enteric coating agent are used to treat the mucosal surface of the gastrointestinal tract. Fluids should be administered to treat the bird for dehydration. The bird should be placed in a quiet ventilated area with access to heat lamps in order to stabilize its body temperature.
In order to remove oil from the feathers of an oiled bird, large (300 gallon) quantities of 103° to 105°F water is needed over a 20-minute period to wash one bird. The water must be above 102°F to remove the oil but can't be over 105°F as it could harm the bird. Dawn dishwashing detergent (Proctor and Gamble) has been the most effective cleaning agent used. After removing the oil in up to 6 tubs of soap and water, the cleaning agents should be rinsed from the feathers with warm, 103° to 105°F, clean water.
For specific details of treating oiled birds, refer to:
- C. Berg. 2003. Best practices for migratory bird care during oil spill response. USFWS. 82pp.
- L. Frink and Dr. E. A. Miller. 1995. Principles of Oiled Bird Rehabilitation. 8 pp. in Wildlife and Oil Spills: Response, Research, and Contingency Planning.
- Tri-State Bird Rescue and Rehabilitation, 170 Possum Hollow Rd, Newark, DE 19711; (302) 757-9543; www.tristatebird.org
- International Bird Rescue Research Center, 4369 Cordelia Road, Fairfield, CA 94534; (707) 207-0380; www.ibrrc.org
The control of oil intoxication is directed at prevention of environmental oil contamination and prompt reporting of any spills.
While oil intoxication is not a major mortality factor affecting Michigan wildlife, sporadic cases are seen occasionally in waterfowl due to small oil spills. These cases are seen most frequently in the winter months when a loss of buoyancy and insulating properties of the feathers results in death due to exposure. There is always the possibility of a large oil spill due to pipelines that are located in the Great Lakes and near streams and rivers in the state. The effects of chronic low-level exposure to oil pollutants in high traffic areas (Great Lakes in Michigan) have not been determined but may significantly alter the physiological and reproductive condition of exposed birds.
For questions about wildlife diseases, please contact the Michigan DNR Wildlife Disease Laboratory.