Chemicals / Complex Chemical Agents / Chemical:
Petroleum Oil

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Information in this page has been entered to support the current volumes of Wildpro and further information will be added as new volumes are completed. Pharmaceutical information on this page is not intended to substitute for the manufacturer's data sheet and the information is not yet complete for all species, or for all contra-indications etc.

Before any pharmaceutical product is used, the manufacturer's data sheet, containing information on uses, dosage and administration, contra-indications, warnings etc., should always be consulted.

General Chemical Information

Petroleum oils vary from crude oils to refined distillates. Components of petroleum oils may be irritant and toxic. Petroleum oils are important as contaminators of wildlife, particularly birds.

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Names and Formulae
  • Petroleum products vary from crude oil to medium and heavy distillates such as Fuel oils No. 1 to 6 (Fuel oil No. 6 is also known as bunker C oil), jet fuel, kerosene, diesel fuel and refined light oils such as petrol (gasoline).
  • Oils are mixtures of hydrocarbons (usually more than 75%) and non-hydrocarbons, and vary greatly in their chemical composition, even within a single class of product and even if coming from a single source. Composition also changes over time due to weathering: a combination of evaporation, oxidation, polymerization, dissolution and biological degradation of oil in the environment. 
  • Oil, unlike most pollutants (which mix with water and are diluted), remains concentrated at the surface of the water for long periods.
  • Many of the toxic effects may be due to polycyclic aromatic hydrocarbons (PAHs). Volatile components such as benzene, toluene and hexane are also highly toxic but evaporate rapidly; these are usually problematic only early during an oil spill, but may remain at toxic concentrations for longer in very cold weather .
  • N.B. Large scale oil spills account for only about 15% of the total quantity of petroleum released into the environment annually. Most oil is introduced into the environment by intentional discharges from transport and refining operations, industrial and municipal discharges, disposal of used lubricants and other waste oils, urban run-off, river run-off and atmospheric deposition. Oil also enters the environment from natural seeps.

(J1.32.w6, J14.19.w1, B15, B18, B20.13.w10, B23.38.w2, B36.42.w42, P4.1990.w1, P9.1.w3, P10.28.w1, P14.2.w6, P62.1.w1)

The relative amounts of different components of oil vary between different oil fractions and between crude oils from different sources or even from the same source but obtained at different times. (P14.3.w12)

About 50 to 98% of liquid crude petroleum may consist of hydrocarbons (containing only carbon and hydrogen); sulphur, oxygen, nitrogen and various metals may also be present, bound to organic compounds or as inorganic salts. (B368.1.w1)


  • Up to 90% of crude oil consists of non-aromatics. These are linear and short branched aliphatics which are generally considered to have low toxicity.
  • These components may be topical irritants due to their solvent characteristics.
  • Inhalation of these components may cause a narcotic effect.


Nonaromatic petroleum compounds include:

  • Alkanes (straight or branched chains, or rings, fully saturated with hydrogen and with carbon atoms linked by single chemical bonds). Alkanes include the n-alkanes, cycloalkanes and isoalkanes. (B20.13.w10, P24.335.w11)
  • Alkenes (similar but not fully saturated with hydrogen and having some carbon-carbon double bonds). (B20.13.w10)
  • Alkanes and alkenes have been shown to be relatively non-toxic fractions of petroleum oils. (B20.13.w10)


Aromatic hydrocarbons contain benzene rings. (B20.13.w10)

  • Up to 10% of crude oil consists of aromatics, which are volatile cyclic compounds. (P14.3.w12)
  • These components include benzene. (P14.3.w12)
    • Benzene vapours are toxic and can be fatal at high concentration. (P14.3.w12)
    • Anaemia and leukaemia may result from prolonged exposure to benzene vapour. (P14.3.w12)
    • In laboratory animals prolonged exposure to benzene vapour has been associated with fetal defects. (P14.3.w12)
    • Concentrations of benzene may be very high above boomed oil. (P14.3.w12)
    • Absorption through intact skin is poor but absorption is enhanced if skin is injured. (P14.3.w12)
  • Low molecular weight aromatic hydrocarbons such as benzene, toluene and xylene are volatile and readily vapourise. (P24.335.w11)
  • Acute toxicity of aromatics is inversely proportional to their molecular weight. Monocyclic aromatics (benzene, toluene, xylene) are very volatile and are rapidly lost to water. Aromatics with four or more rings are rarely present in toxic concentrations. Naphthalenes and phenanthrenes, being slightly soluble and relatively persistent, "contribute most to the toxicity of crude and refined petroleum." "Heterocyclic compounds can have a toxicity similar to the analogous aromatic hydrocarbons." (B368.1.w1)


  • Polycyclic aromatic hydrocarbons (PAH) are hydrocarbons containing two or more benzene rings. (B20.13.w10, P24.335.w11)
  • The smallest PAH compound is napthalene.
  • PAH are relatively nonvolatile and insoluble in water and tend to increase in concentration in the remaining oil during weathering. (B20.13.w10)
  • PAH compounds have been implicated as being responsible for at least some aspects of petroleum oil toxicity. (B20.13.w10)
  • PAHs in combination with other hydrocarbons produce polymeric structures which are important components of resins and asphaltene. (P24.335.w11)

Napthalenes cause haemoglobin denaturation and are one of the compound groups responsible for the development of haemolytic anaemia in oiled wildlife. (B20.13.w10)

PAH compounds have been shown to be responsible for toxic effects of petroleum oils observed causing mortality of avian embryos. (B20.13.w10)

PAH compounds have been shown to be responsible for toxic effects of petroleum oils observed experimentally on ingestion of oil by Larus argentatus - Herring gull chicks. (B20.13.w10)

  • Less than 1% of crude oil is composed of polyaromatic hydrocarbons. (P14.3.w12)
    • Some of these compounds, such as bezo(a)pyrene have been identified as skin carcinogens.(P14.3.w12)
    • These compounds persist in aged oil. (P14.3.w12)
    • These compounds may be absorbed through intact skin and their absorption is facilitated through traumatised skin. (P14.3.w12)

Heterocyclic hydrocarbons:

  • These compounds, in addition to carbon and hydrogen, contain atoms of other elements such as nitrogen, oxygen and sulphur and variable concentrations of metals (e.g. mercury, vanadium, lead, nickel). (B20.13.w10)
Alternative Names
  • Crude oil
  • Fuel oil
  • Kerosene
  • Diesel
  • Petrol
  • Gasoline
  • Bunker oil
Chemical Formula --
Chemical Structure Highly variable. (J68.297.w1)
Molecular Weight Highly variable. (J68.297.w1)
  • "Crude petroleum may contain organic compounds ranging in molecular weight from methane to complex polymeric structures such as asphaltanes with molecular weights of 100,000 or more." (B368.1.w1)
Related Chemicals --

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Physical Properties / Chemistry

Petroleum oils vary in appearance from clear liquids to brown or black viscous liquids and dark sticky solids.

Melting point --
Boiling point
  • Highly variable: some components are gaseous at room temperature, others have boiling points of more than 350 C. (J68.297.w1)
    • 0-70C for light gasolines; (J68.297.w1)
    • 140-250C for paraffins; (J68.297.w1)
    • 250-350C for diesel fuels (gas oils); (J68.297.w1)
    • > 350C for heavy fuel oils. (J68.297.w1)
  • Highly variable: 0.70 to about 1.00 for those compounds which are liquid. (J68.297.w1)
    • 0.8 for paraffins; (J68.297.w1)
    • 0.82-0.85 for diesel fuels (gas oils); (J68.297.w1)
    • about 1.00 for heavy fuel oils. (J68.297.w1)
Water solubility --
Other solubility --
Acid/Base --

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Pharmacology & General Information
Pharmacology N/A
Storage / Stability --
Legal Category (In UK) --

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Associated Techniques




(Further Reading)
Click image for full contents list of ELECTRONIC LIBRARY

Authors Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referees Dr Virginia Pierce (V.w73)

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Therapeutic Information

Activity --
Appropriate Use --
Limitations --
Notes --

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Pharmacokinetics and Drug Interactions
Absorption /Bioavailability --
Distribution --
Plasma Protein binding / Storage --
Elimination Route --
Elimination half-life / Clearance Rate --
Drug Interactions --

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Formulations available --
Doses / Administration Routes / Frequencies --
Monitoring parameters --

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Withdrawal period / Withholding time
Notes --

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Toxic Information

Toxic effects of Pharmaceutical Products
Contraindications / Precautions --
Adverse Effects / Side Effects / Warnings --
Operator Warnings --
Overdose / Acute Toxicity --

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Detailed Toxicological Information
Classification --
Acute Toxicity "The evidence that petroleum oils are, indeed, toxic to birds is overwhelming". (P14.2.w62)

Acute effects of oil include:

  • Physical effects on skin, fur and feathers result in loss of water repellant properties of feathers (in birds) or pelage (in mammals) and resultant hypothermia. (B20.13.w10)
  • Irritation of the skin and of oral, ocular, respiratory and gastro-intestinal mucous membranes. (B20.13.w10)
    • Irritant effects on the eyes, lungs and other systems may decrease the ability of affected individuals to oxygenate blood and to capture prey. (B20.13.w10)
  • There may be damage to the renal system and to the hepatic enzyme systems responsible for metabolism of toxins and other compounds. (B20.13.w10)
  • Immune system suppression. (B20.13.w10)
  • Haematopoisis disruption or suspension. (B20.13.w10)

Napthalenes cause haemoglobin denaturation and are one of the compound groups responsible for the development of haemolytic anaemia in oiled wildlife. (B20.13.w10)

PAH compounds have been shown to be responsible for toxic effects of petroleum oils observed experimentally on ingestion of oil by Larus argentatus - Herring gull chicks. (B20.13.w10)

Physiological disruptions caused by petroleum oils include altered endocrine function, liver and kidney disorders, altered blood chemistry, blood disorders including anemia, impaired salt (nasal) gland function resulting in disruption of osmoregulation. (B36.42.w42)

Effects of external contamination of birds:

  • Oil is rapidly absorbed by feathers, resulting in loss of the normal waterproof structure, matting of feathers, exclusion of air and resultant loss of insulation, waterproofing and buoyancy. (B20.13.w10, P14.3.w2)
  • Plumage disruption compromises the ability of oiled birds to fly, swim, dive, feed and escape predators. (B20.13.w10)
  • There is a direct irritant effect on the skin and eyes. (P24.327.w4)
  • Hypothermia due to loss of insulative qualities of feathers. (J40.31.w2, P24.327.w4, P14.3.w2)
  • Penetration of water to the skin causes considerable increase in heat loss. Metabolic rate must be increased to compensate for loss of insulation. (P14.1.w1, P14.3.w2)
    • A 400% increase in metabolic rate was noted in Somateria mollissima - Common eider experimentally contaminated with oil (externally) and maintained on cold water. (B20.13.w10, P14.3.w2)
    • In Anas platyrhynchos - Mallard following experimental oiling and exposure to a range of environmental temperatures, metabolic rate was found to increase substantially; below the lower critical temperature, the rate of energy metabolism appeared to increase linearly with decreasing ambient temperature. The rate of heat loss increased most rapidly for low levels of oiling, tending to level off for heavier oiling. Heavily oiled ducks may have heat losses more than twice those of unoiled ducks. Oiled ducks with good fat reserves could survive exposure to low ambient temperatures (-26C) for longer than could ducks in poor condition at the same degree of oiling. (J40.31.w2)
    • Anas platyrhynchos - Mallard exposed to oil experimentally by swimming for one hour on water contaminated with Prudhoe Bay crude oil, then placed in a respiration chamber, air temperature -15 C, showed a significant increase in metabolic rate. (J53.29.w1)
    • Pygoscelis adelie - Adelie penguins (Spheniscidae - Penguins (Family)) which were oiled, compared to unoiled controls, had reduced heart rates (90 bpm versus 98 bpm), reduced body temperature (39.6 C versus 39.2 C) and reduced energy expenditure (4.7 W/kg versus 5.2 W/kg). When placed in a swim tank, oiled penguins attempted to leave the water and showed erratic swimming behaviour. They had a reduced swimming speed (1.6 m/s versus 1.8 m/s), increased heart rate while on the water surface (321 bpm versus 252 bpm), a 50% higher metabolic rate (18.8 W/kg versus 12.7 W/kg) and a much higher (73%) cost of transport (12. 1 J/kg/m versus 7 J/kg/m). (J313.22.w1)
    • A study of Cerorhinca monocerata - Rhinoceros auklets (Alcinae - Laridae - Skuas, Terns, Gulls, Puffins, Auks (Family)) in the Southern Japan Sea, found that dead oiled birds had lost one third of body, muscle and general organ masses, 60% of liver mass, more than 90% of subcutaneous fat and more than half of all fats stored in muscles and other organs, including bone marrow, which was almost entirely replaced with water. It was considered that these birds died within one to two days, not from the oiling per se but from "emaciation caused by starvation and nutritional exhaustion, accelerated by increased energy loss." (J313.40.w3)
    • A study of common eiders (Somateria mollissima - Common eider) experimentally oiled by exposure to Statfjord A crude oil (12.5 mL on a 50 L tank of water, i.e. 100 mL oil per m water surface) showed that their insulation was reduced to just 22% of the unoiled value. Metabolic heat production increased to about 4.5 times that of unoiled birds and, despite this, body temperature was lower than in nonoiled birds. (J59.16.w1)

Internal effects of oil on birds:

  • Birds may ingest oil while attempting to preen it from their feathers, by drinking from contaminated water or by eating contaminated food. (B20.13.w10, P24.327.w4, P24.335.w11)
  • A study on the uptake and clearance of petroleum hydrocarbons in Larus glaucescens - Glaucous-winged gulls (Larus (Genus)) and Anas platyrhynchos - Mallard found that about 45% of the ingested oil was excreted. Labeling indicated that the absorbed petroleum hydrocarbons were distributed to various body tissues, and that these hydrocarbons are removed by detoxifying mechanisms. In the gulls, levels were highest in fat, kidney and liver and lower in muscle and plasma; radioactivity leveled off after 24 hours. In ducks, levels were highest in plasma and kidney, and lower in liver, muscle and fat; levels returned to background after 24 hours. It was noted that levels in the liver and kidney of the gulls were higher than in duck tissues. (J30.58.w1)
  • Toxins, particularly PAH, absorbed through the skin, respiratory tract or gastro-intestinal tract, may affect the liver, kidneys, nervous system, blood and gonads. (P24.327.w4, P24.335.w11)
  • Reported effects of ingested oil include:
    • Anaemia. (B20.13.w10)
    • Stressor effects (in which it may be additive with other stressors such as cold temperatures). (B20.13.w10) N.B. Petroleum products appear to be highly unpalatable. Individuals forced to ingest oil may find this an additional stressor. (P24.335.w11)
  • Birds may inhale petroleum fumes or vapours. (P24.327.w4)
  • Birds may absorb toxins from oil through the skin or mucous membranes. (P24.327.w4)
  • Gastro-intestinal tract: 
    • General irritation, ulceration, destruction of the GIT microstructure. (D183.w3)
    • Ingested oil causes gastroenteritis (inflammation, ulceration and haemorrhage of the gastrointestinal tract mucosa), maldigestion and malabsorption including reduced absorption of sodium and water. (P24.327.w4, P24.335.w11)
    • Clinically, the effects of ingested oil may be seen as diarrhoea, dysentery and vomiting. (P24.327.w4, P24.335.w11)
    • Bacterial infections may occur secondarily. (P24.327.w4, P24.335.w11)
    • Damage to the GIT contributes to dehydration, anaemia and protein loss leading to hypoproteinaemia. (P24.327.w4, P24.335.w11)
    • Nutrient absorptive capacity of the intestine may be reduced due to damage to absorptive cells. (P14.1.w17)
    • Larus argentatus - Herring gull chicks of about four- to five-weeks-old, maintained on unsalted herring and 50% sea water as drinking water, dosed (by intubation) with 0.2 ml (about 0.3 ml per kg bodyweight) of South Louisiana crude (17% aromatics), were found at necropsy (when sacrificed after eight to nine days) to have histopathological changes of the GIT: proliferative oedema of the intestine, with considerable cytoplasmic disruption and numerous lipid droplets in the epithelial mucosa. Fewer and smaller droplets were found in tissue sections from one of two chicks which had been given 0.2 ml of Kuwait crude. (J22.199.w1)
  • Respiratory:
    • Inhalation of volatile components of oil, or aspiration of oil, for example while preening, may result in pneumonia. (P24.327.w4, P24.335.w11)
    • Volatile components may cause pulmonary haemorrhage and oedema. (P24.327.w4, P24.335.w11)
  • Red blood cells:
    • Decreases in packed cell volume or blood haemoglobin concentration have been reported following single or chronic ingestion of oil by mallards. (P14.2.w6)
    • Anaemia often occurs about four to six days after oil ingestion and is consistent with oxidant chemical damage to haemoglobin, resulting in haemolysis. (P24.327.w4, P14.3.w2, P24.335.w11)
      • This is seen more commonly with crude oil and is less evident with diesel or home heating oils. (P24.327.w4, P24)
      • Feeding of herring gulls with 10 m/kg per day crude oil caused marked changes in conformation of erythrocytes and formation of Heinz bodies. (P24.327.w4)
      • Destruction of up to 50% of circulating blood cells, with resultant severe anaemia, has been seen in birds following experimental ingestion of crude oil. Heinz bodies (visible masses of oxidised haemoglobin) were seen in 50-100% of erythrocytes of these birds. Ultrastructural findings and biochemical indicators were consistent with primary oxidant damage. (P14.2.w6, P14.3.w2, P24.335.w11)
      • Metabolic rate must be increased to compensate for severe anaemia. (P14.2.w6)
      • Stress, infection and chronic debilitating disease may further add to the anaemia by suppressing erythropoisis. (P24.335.w11)
      • In Melanitta fusca - White-winged scoter held in care following oiling with bunker C fuel oil, sampling 12 days after the birds were caught revealed low red blood cell count, PCV (haematocrit) and haemoglobin; values had increased significantly from these levels by day 26 of treatment. Many polychromatic erythrocytes, indicative of elevated haematopoisis, were also observed in samples taken on day 12, and livers of birds which did not survive showed marked haemosiderin deposits in the liver, and sometimes in spleen, kidney and even lung. The findings were considered to suggest haemolytic anaemia in the birds resulting from ingestion of oil following oiling. (J1.32.w6)
  • Other organs:
    • Kidney damage may be caused directly by oil toxins or secondarily due to dehydration. (P24.327.w4)
    • Immune system suppression: This may be a toxic effect of oil or secondary to stress (due to oiling, cleaning, or rehabilitation). (P24.327.w4, P24.335.w11)
      • Mortality of Eudyptula minor - Little penguins (Spheniscidae - Penguins (Family)) during rehabilitation following oiling was thought to be associated with immune system depletion due to oil toxicosis, as well as due to stress from capture and handling. (J3.130.w5)
    • Liver: ingestion of petroleum oil or aromatic fraction of oil can induce dose-related increased activity of hepatic mixed-function oxidases (MFO). Increases in liver weight have commonly been reported following oil ingestion and increased levels of liver enzymes, indicative of liver damage, have been reported in some, but not all, studies. (P14.2.w6, P24.335.w11)
      • Rises in liver enzymes may reflect increased hepatic activity. (P24.335.w11)
      • Larus argentatus - Herring gull chicks of about four- to five-weeks-old, dosed (by intubation) with 0.2 ml (about 0.3 ml per kg bodyweight) of either Kuwait crude (22% aromatics) or South Louisiana crude (17% aromatics), showed significant liver hypertrophy and induction of hepatic microsomal cytochrome P-450 activity when euthanased and necropsied eight to nine days after dosing with the oil. (J22.199.w1)
      • In Cepphus columba - Pigeon guillemots (Cepphus (Genus)) in Alaska, eight years after the Exxon Valdez oil spill in Prince William Sound, increased levels of AST and lowered levels of GGT were found in adults from an oiled area, compared to adults from an area unaffected by the spill. It was noted that the increased AST suggested liver injury, but that since birds were sampled opportunistically, the possibility of some differences being related to breeding season could not be ruled out. (J313.40.w1)
      • Feeding 100 mg or 500 mg of weathered crude oil (weathered for two weeks) to Larus glaucescens - Glaucous-winged gulls (Larus (Genus)) for 30 to 134 days, did not significantly affect liver function, as indicated by metabolism of testosterone. Mean percentages of testosterone converted to polar metabolites did not show a significant change in those fed 500 mg oil compared to those fed 100 mg or no oil. Gulls fed 500 mg oil daily produced significantly less nonpolar metabolites of testosterone than did those fed no oil or 100 mg oil daily. Overall the study indicated that ingestion of weathered oil did not significantly induce testosterone-metabolising enzymes. (J30.56.w2)
      • When adult Oceanodroma leucorhoa - Leach's storm-petrel were dosed with 0.1 ml Prudhoe Bay crude oil (2.5 ml per kg bodyweight), livers collected from sacrificed birds 14-21 days later did not show significant hypertrophy. (J55.86.w1)
    • Osmoregulation: This has been noted to be affected by oiling; the effect may be due to effects of oil on the gastrointestinal tract, kidneys or salt glands. (P24.335.w11)
      • Larus argentatus - Herring gull chicks of about four- to five-weeks-old, maintained on unsalted herring and 50% sea water as drinking water, dosed (by intubation) with 0.2 ml (about 0.3 ml per kg bodyweight) of Kuwait crude (22% aromatics) showed slightly elevated plasma sodium levels compared to controls, while those dosed with South Louisiana crude (17% aromatics), showed significantly raised plasma sodium on days six, eight and nine after dosing, indicating disruption of salt and water balance. At necropsy following euthanasia after eight to nine days, the nasal glands showed 30% reductions in specific activity of sodium-potassium-ATPase, together with hypertrophy of nasal gland tissue, so that total activity of the glands was reduced by only 20% in the gulls given South Louisiana crude, and was not significantly reduced in those given Kuwait crude. (J22.199.w1)
      • In a study on Larus glaucescens - Glaucous-winged gulls (Larus (Genus)), fed 1.0 g of bunker C fuel oil or marine diesel oil followed three hours later by oral administration of 3% of body weight of 0.5% sodium chloride (salt water), no effect was found on the ability of the birds to regulate sodium chloride uptake from the gut and excretion by the kidney. (J30.56.w1)
      • When adult Leach's storm-petrels (Oceanodroma leucorhoa) were dosed with 0.1 ml Prudhoe Bay crude oil (2.5 ml per kg bodyweight), nasal glands and adrenals collected from sacrificed birds 14-21 days later showed significant hypertrophy. (J55.86.w1)
    • Growth:
      • Larus argentatus - Herring gull chicks of about four- to five-weeks-old, maintained on unsalted herring and 50% sea water as drinking water, dosed (by intubation) with 0.2 ml (about 0.3 ml per kg bodyweight) of Kuwait crude (22% aromatics) failed to put on weight in the eight to nine days following dosing with the oil, compared with a growth rate of about 3% per day in control non-oiled birds; this was not due to decreased food intake. Reduced growth rate had also been seen in immature birds in wild nests given 0.2 ml of Kuwait crude (about 0.6 ml/kg bodyweight), compared to non-oiled chicks from the same nest. (J22.199.w1)
      • Wild Larus argentatus - Herring gull chicks of between 10 and 20 days of age (200-500 g bodyweight), dosed via stomach tube with 0.2 ml or 0.5 ml of weathered South Louisiana crude oil, showed reduced weight gain 7-9 days after dosing, compared with control birds given (non-toxic) corn oil. Weight gain had recovered by 11-13 days in chicks given 0.2 ml oil, but was still depressed at 11-13 days and through 18-22 days in chicks given 0.5 ml of the crude oil. Additionally, both groups given petroleum oil showed significant decreases in culmen growth on days 7-9 and 11-13, compared with controls, although rates of toe growth were not significantly affected. The birds given the higher dose of oil also showed a slightly lower survival to 700g/20 days: 41% survival, compared with 62% for control birds and 65% for those given the lower dose of oil. Behaviour of the chicks was not significantly affected. It was not possible to state whether the observed growth depression was due to direct pollutant-induced impairment of nutrient utilisation, and/or a direct effect on endocrine system function, or whether it was due to non-specific stress due to the oil. (J50.96.w1)
      • A study on fledgling/nestling Rissa tridactyla - Black-legged kittiwake found that those with internal oiling, detected by the presence of oil in the gastro-intestinal tract, had lower body weights and lower liver weights than those without internal oiling. (J313.19.w1)
      • When adult Leach's storm-petrels (Oceanodroma leucorhoa) were dosed with 0.1 ml Prudhoe Bay crude oil (2.5 ml per kg bodyweight) while brooding chicks of two- to three-days-old, chick survival for 21 days was reduced from 100% (in chicks of control sham-dosed birds) to 70% if one adult was dosed with oil and to 52% if both parents were dosed; mortality of chicks occurred within six days of the oil dose. Chicks also showed reduced weight gain compared to those of un-oiled adults (1.5 +/- 0.2 g/day for controls, 0.7 +/- 0.2 g/day for single oiled adult, 0.5 +/- 0.2 g/day if both adults were oiled, for chicks surviving three days, P<0.01 for both groups). When adults were dosed when chicks were 10-15 days old, no chicks died but weight gain decreased significantly, with no significant weight gain during the six days after the adults were dosed; even after 21 days there were still significant differences in rate of weight gain compared with control chicks. The effects were considered probably due to the oiled adults having impaired ability to provide their chicks with food. Giving oil to the chicks directly (0.05 ml at 10-15 days old) did not affect their weight gain in the 21 days after dosing. It was commented that younger chicks were probably less able than older chicks to survive a period of reduced feeding, and that in conditions of additional stress such as food shortages, survival of older chicks may be reduced post-fledging, due to reduced fat reserves. (J55.86.w1)
    • Metabolic rate:
      • In an experiment using double-labelled water in adult Oceanodroma leucorhoa - Leach's storm petrels, birds dosed by intubation with 0.1 ml of Prudhoe Bay crude oil showed significantly (P<0.001) higher standard metabolic rate than did control birds which were not given oil. This suggested that the metabolic rate of adult birds may be temporarily increased following ingestion of small amounts of oil, for example while trying to preen fouled plumage, or by consuming contaminated food), as well as the known increase in metabolic rate in response to reduced insulation from oiled plumage. (J55.88.w1)

Note: Toxicity may be exacerbated in individuals under stress: in ducks fed a variety of petroleum oils by stomach tube, the oils were relatively nontoxic in individuals maintained under optimum conditions, but were much more toxic, with a lower LD50, in stressed ducks kept outside in temperatures of 0 to 10 C under crowded conditions (e.g. for diesel oil, LD50 of 4 mL/kg under stress conditions, compared with survival when given up to 20 mL/kg and maintained under optimal conditions). (J40.30.w2)

Effects of oil on mammals:

  • "Hypothermia, stress, shock, respiratory compromise associated with interstitial emphysema, hemorrhage from gastric erosions, and hepatic necrosis" were thought to contribute to the deaths of oiled Enhydra lutris - Sea otters following the Exxon Valdez oil spill. (P14.3.w28)
  • Mammals covered with fresh oil are likely to inhale toxins and may suffer toxic effects on the mucous membranes and respiratory system. (P14.2.w5)
  • Species which rely on their fur for insulation are more vulnerable than those which rely primarily on blubber for insulation, and are more likely to show mortality after oiling. This includes otters, newborn Phocidae - Seals (Family) seal pups, fur seals (Otariidae - Sea lions (Family)) and polar bears (Ursus maritimus - Ursidae - Bears (Family)). (B335.15.w15, P14.2.w1, P14.2.w5)
    • In Enhydra lutris - Sea otters, pelt studies showed a two- to four-fold increase in thermal conductance when oiled pelts were immersed in sea water. Mean thermal conductance for unsoiled pelts was 7.64 +/- 1.30 W/(m.C). Weathered oil caused less increase in thermal conductance (mean increase of 4.1 W/(m.C) than either fresh crude (mean difference 16.9 W/(m.C)) or fresh crude plus a dispersant (mean increase of 12.6 W/(m.C)). (J30.66.w2)
    • In Enhydra lutris - Sea otters, in which about 17.5% of the fur was experimentally oiled with 38 to 60 mL of Prudhoe Bay crude oil, following oiling and then washing of the fur, the insulating quality of the fur was significantly reduced, acting as an energetic liability and requiring an increase in oxygen consumption: even in water of 15C average maintenance oxygen consumption doubled following oiling and washing. At least eight days were required to return average oxygen consumption to normal. In one otter left oiled for eight days, by day six the average metabolic rate had increased by 98% above baseline, to 37.6 mL 02/kg/min. Otters placed in holding tanks at 16C after oiling and washing shivered constantly. Subcutaneous temperatures beneath the oiled areas of fur decreased, indicating peripheral vasoconstriction under the oiled areas, although this effect was transitory, with the subcutaneous temperature rising again by one day after oiling. The reduction in insulation after oiling appeared to be due to fur clumping and, due to this, loss of the trapped layer of air beneath the fur. It was noted that washing would remove the fur's natural oils and therefore reduce its water repellency. Whole body heat conductance increased considerably following oiling and following oiling-and-washing, even with only about 20% of the pelt oiled. It was noted that should the animals be oiled all over the body and then remain in the normal water temperatures of their environment, it would be unlikely that they could maintain metabolism sufficiently high to offset the increased heat loss for the extended period that oil would remain soiling the fur. (J30.60.w1)
    • When Enhydra lutris - Sea otters were experimentally oiled with a "sour crude" oil containing highly volatile sulphur, applied in a band across the chest using a brush, to cover 20% of the body surface area, and placed in water at 13 C, thermal conductance of the otters increased 1.8 times; the otters increased average metabolic rate 1.9 times, by shivering and voluntary activity in order to maintain core body temperature. Time spent grooming and swimming was increased 1.7 times, with resting time reduced (grooming time increased from 35% to 61%, swimming from 10% to 17%, while resting in water decreased from 45% to 12%). The fur was then cleaned using detergent (Dawn; Proctor and Gamble), followed by rinsing; this obviously removed the natural oils (squalene) from the fur, and three to six days, plus grooming activity by the otters, were required to return core body temperature, baseline metabolic rate and thermal conductance to base-line (pre-oiling) levels. In cleaned otters 49% of time was spent grooming and time spent shivering was increased, particularly in animals which did not groom well. It was noted that in order to double the average metabolic rate, as would be required following oiling, an otter in the wild would have to increase daily food intake to 40-50% of body weight per day, requiring 40-100% of its time to be spent in foraging (depending on location and season); since capturing and digesting this about of food each day may not be possible, the otter would go into negative energy balance, metabolise body protein, rapidly lose weight, have increased susceptibility to disease, and die. It was recommended that, following cleaning, at least one to two weeks should be allowed for the animals to restore fur insulation and recover from the stresses of oiling and cleaning. With severe oiling, even in captivity with food provided, it may be necessary to maintain oiled sea otters in warm water (e.g. 25C, rather than normal water temperatures (e.g. 13C), in order to ensure that energy balance is maintained. (J30.66.w1)
    • When muskrats Ondatra zibethica (Muridae - Rats, mice, voles, gerbils etc. (Family)) were oiled experimentally with varying quantities of crude oil, by swimming in water contaminated with oil, the muskrats showed attempts to escape from the tank, preening and shivering. Subsequently the muskrats showed an increase in heat production above that of control individuals from 20% in lightly oiled to 119% in heavily oiled muskrats, reducing on subsequent days, although still about 20% above control values on day three in heavily oiled muskrats. There was a seven-fold difference between metabolic rates of unoiled and heavily oiled musk rats held at 5C on the day of oiling. Thermal conductance increased by up to 122%. Food intake of oiled animals increased markedly, with the greatest increase recorded in animals with the greatest oiling. Heavily oiled individuals preened more than did lightly oiled individuals, resulting in loss of considerable quantities of underfur and making the guard hairs stay erect. Heavily oiled animals also stayed out of water for up to ten days. It was considered that, for these animals which depend on water for feeding and refuge, even moderately oiled animals would have been unable to meet their high energy requirements in the wild. (J30.52.w1)
  • Instability of body temperature has been noted in oiled Enhydra lutris - Sea otters. (B20.13.w10)
  • In all mammals coming into contact with spilled petroleum oils, irritation of the skin and eyes may occur, also interference with normal swimming of aquatic mammals. (P14.2.w1)
  • Corneal ulceration has been recorded in heavily oiled harbour seals (Phoca vitulina - Common seal). (P14.2.w5)
Internal effects:
  • Large quantities of ingested oil may cause renal failure and blood disorders and be lethal to polar bears Ursinus maritimus (Ursidae - Bears (Family)). (P14.2.w1)
  • Ingestion of oil may cause gastrointestinal haemorrhage in Lutra lutra - European otter. (P14.2.w1)
  • Both oil toxicity and stress are believed to have contributed to gastrointestinal haemorrhage (resulting in melaena) and chronic gastric erosion in oiled Enhydra lutris - Sea otters. (B20.13.w10)
  • Seals and cetaceans are able to metabolise petroleum oils and show rapid renal clearance, which minimises the toxic effects of ingested oil on these species. (P14.2.w1)
  • Weight loss has been recorded, probably due to increased metabolic demand, hypoglycaemia, lethargy and anorexia. (B20.13.w10)
  • Levels of various liver enzymes such as AST and ALT may be increased. (B20.13.w10)
  • Liver lipidosis and centrilobular necrosis may occur due to hypoglycaemia and shock secondary to hypothermia resultant from oiling. (B20.13.w10)
  • Severe leucopaenia and a left shift seen in oiled Enhydra lutris - Sea otters, indicating a severe inflammatory response, may be partly due to severe stress and use of corticosteroids. (B20.13.w10)
  • Inhalation of volatile hydrocarbons may result in mucous membrane inflammation, pulmonary oedema, pulmonary haemorrhage and pneumonia. (P24.327.w4)
  • Dyspnoea in Enhydra lutris - Sea otters, with associated interstitial pulmonary emphysema. (B20.13.w10)
  • Volatile hydrocarbons may be distributed systemically resulting in anaemia, and may accumulate in the brain or liver. (P24.327.w4)
  • In domestic cattle calves experimentally dosed with oil (high-sulphur sour crude, low-sulphur sweet crude or kerosene), the most serious consequence appeared to be aspiration pneumonia; bloat was also seen. It was considered that aspiration occurred more readily, and caused a more fulminating pneumonia, in calves given oil containing large amounts of light hydrocarbon fractions (kerosene, naphtha or gasoline), and that with more volatile oils than kerosene, bloat could be an important cause of death. (J4.162.w1)
  • Ingestion of oil may cause hepatic toxicity and blood disorders in Mus domesticus - Laboratory mouse and blood disorders in laboratory rats (Rattus norvegicus - Brown rat). (P14.2.w1)
  • In addition to acute physical and toxic effects of oil, oiling of mammals may lead to abnormal reproductive behaviour, increased embryonic death, lowered survival rates of young and increased abandonment of young. (D183.w3)
  • Oil on unweaned seal pups may disguise the smell of the pup and thus interfere with maternal recognition of the pup; this may result in abandonment. (P24.327.w4)

Effects of oil on reptiles:

  • Reptiles have been killed by oil, such as a spill of bunker C oil. (P14.2.w1)
  • Inhalation of volatile hydrocarbons may result in mucous membrane inflammation, pulmonary oedema, pulmonary haemorrhage and pneumonia. (P24.327.w4)
  • Sea turtles may ingest oil and tar balls; these have been found in the mouth, oesophagus and stomach. (D183.w3, D228.4.w4)
  • Oil may have adverse effects on respiration, blood chemistry, energy metabolism, diving patterns and salt gland function. (D183.w3)
  • Effects of tarballs in the gut of turtles may include starvation due to blockage of the gut, local necrosis or ulceration at the site of blockage, interference with fat metabolism, and, due to build up of fermentation gases, buoyancy problems, preventing feeding and increasing vulnerability to predation and boats. (D228.4.w4)
  • Since oil remains in the intestinal tract of turtles for several days there is considerable time for absorption of toxins. (D228.4.w4)
  • Caretta caretta - Loggerhead turtles experimentally exposed to oil showed gross and histological skin lesions consistent with a contact/irritant dermatitis. Dysplastic change was sometimes marked. Most changes had resolved by 10 days after cessation of exposure to the oil. It was noted that the nature of the inflammatory response could break the integumentary barrier and allow entry of pathogenic organisms, resulting in localised bacterial infection and even septicaemia. (P14.3.w29)
  • Haematocrits of oil-exposed turtles decreased by nearly 50%. (D228.4.w4)
  • In sea turtles, which do not seem to avoid contact with oil slicks, "physical contact with, and ingestion of, oil has been described as causing dermatological damage, detrimental respiratory changes, a decrease in digestive efficiency, hematological damage that elicits a profound immune reaction, and a decrease in the efficiency of the salt gland, which maintains osmotic and ionic balances." (B369.w6)

Effect of oil on amphibians:

  • Amphibians have been killed by oil, such as a spill of bunker C oil in the St. Lawrence River. (P14.2.w1)
  • Amphibian larvae show sensitivity to fuel oils and crude oils similar to that seen in fish larvae. (P14.2.w1)
  • Rana catesbeiana - bullfrog (Rana (Genus)) tadpoles exposed to No. 6 fuel oil, in amounts similar to those expected to be found in shallow waters after an oil spill, were adversely affected. All tadpoles showed abnormal behaviour; mortality was highest in tadpoles in the late stages of development. (P14.2.w1)
Chronic Toxicity Immune function:
  • Oil ingestion may cause functional immunosuppression and thus an increased susceptibility to infectious disease. (P14.2.w6)
    • Following daily dosing with various oils for 28 days, mallard ducks showed increased mortality following inoculation with Pasteurella multocida (the causative agent of Avian Cholera). (P14.1.w5)
  • Reduced immunological function may result in increased susceptibility to disease. (B36.42.w42)
  • River otters from oiled areas had elevated interleukin-6 levels, suggesting a long-term inflammatory response which could result in impairment of the immune system. (B20.13.w10)

Adrenocortical function:

  • Exposure to oil-contaminated food (contaminated with South Louisiana crude oil) for one week resulted in "striking declines in plasma corticosterone concentration." Abrupt declines were also found during the first week of exposure to lower levels of crude oil. (P14.1.w4)
  • Anas platyrhynchos - Mallard exposed to petroleum products in their diet showed a reduced ability to cope with stressors such as cold exposure and/or saline drinking water. Oil appeared to have an additive or synergistic effect with other stressors. (P14.2.w6)
  • Oil ingestion experiments have shown both abnormally low and abnormally high levels of plasma corticosterone in response to oil ingestion. (P14.2.w6)
  • Enlarged adrenal glands have been recorded in birds after oil ingestion. (P14.2.w6)
  • Oiling may have effects on annual cycles such as moulting and nesting dates. (B334.w3)
Growth rates:
  • Growth rates of young birds may be reduced following exposure to oil. Different studies have shown different results, however, it has been shown that, at least with some species, ingestion of single or multiple doses of crude oils can significantly reduce growth rate. (P14.2.w6, P24.335.w11)
  • River otters showed abnormal weight/length ratios for up to two years after exposure to oil, as well as inflammatory proteins in the blood. (B20.13.w10) 
    • A study comparing river otters (Lontra canadensis - Canadian otter) living in areas of Prince William Sound, Alaska, that had been oiled by the Exxon Valdez spill in 1989 with those from unaffected areas, found, for 1990-1992, that male otters from the oiled area had significantly (P<0.04) lower body mass for length than did otters from areas that had not been oiled; this was thought probably related to differences in prey availability. Otters from the oiled areas also showed significantly higher levels of serum haptoglobin, levels which could indicate chronic inflammation and liver injury, or infection; the increased level could be due to haemolytic anaemia associated with oil ingestion. (J1.29.w11)
    • A study comparing river otters Lontra canadensis - Canadian otter living in areas of Prince William Sound, Alaska, that had been oiled by the Exxon Valdez spill in 1989, with those from unaffected areas, found, for otters sampled in May-June 1992, that otters from oiled areas still had significantly lower body weights for length than did those from unoiled areas (P = 0.04), but that the mean body mass of otters form the oiled area were higher than for 1990 or 1991, which might indicate some recovery. Additionally, serum haptoglobin levels for otters collected May to June 1992 in the oiled area were not significantly raised, unlike samples from otters collected in this area in 1990-1991. (J1.30.w5)

Other effects:

  • Anaemias were observed to develop in oiled Enhydra lutris - Sea otters after several weeks in captivity. (B20.13.w10)
  • Substantial effects of oil on seabirds and marine mammals can occur over the long term, "through interactions between natural environmental stressors and compromised health of exposed animals, through chronic toxic exposure from ingesting contaminated prey or during foraging around persistent sedimentary pools of oil, and through disruption of vital social functions (care giving or reproduction) in socially organized species." (J22.302.w2)
  • Long term (decade or more) effects have been documented on the population of Enhydra lutris - Sea otters in the area of Prince William Sound, Alaska, heavily oiled during the Exxon Valdez oil spill. By 2000, no population recovery was documented on the heavily oiled northern Knight Island, with sea otter numbers remaining at just half their pre-spill value. Decreased survival in other oiled areas of Prince William Sound has also been documented. (J22.302.w2)
Reproductive effects Toxic effects of oil may include decreased egg production and sperm production, reduced fertility and reduced hatchability. (B36.42.w42)

Effects of oil contamination on avian eggs and embryos:

Contamination of eggs may cause failure of hatching or damage to embryos. 

  • Field observations and experimental trials have demonstrated that oil transferred to eggs from the feathers of incubating oils can cause mortality of embryos. (P14.2.w6)
    • A female Larus marinus - Great black backed gull oiled on the breast and underparts was observed incubating her eggs, which failed to hatch; the eggs were later found to contain partially-developed embryos. It was not possible to determine whether the oil sealed the pores and suffocated the eggs, or whether the effect on the embryos was an effect of oil penetrating the eggs. (J41.66.w1)
    • Eggs of various shore birds failed to hatch after the incubating adults became contaminated by stranded oil. (B378.6.w6)s
  • Embryos of most birds species appear to have similar susceptibility to the embryotoxic effects of oil. (P14.2.w6)
  • Avian embryos are most susceptible to the toxic effects of oil during the first half of incubation. (P14.2.w6)
    • Days 6-10 of incubation appears to be the most sensitive time. (P14.3.w16)
    • In chicken eggs, it was noted that embryos at day nine of incubation were sensitive to the toxic effects of oil, but less sensitive than younger embryos (even those only a day younger). (P14.3.w16)
  • Eggs which are covered completely or almost completely in oil may fail due to gaseous exchange being prevented. (P14.1.w7)
    • However, the toxic effects of crude oil are not accounted for by reduced gas exchange. (P14.3.w16)
  • Toxic effects of smaller quantities of oil deposited on the shells of eggs will vary with the type of oil. Significant reductions in hatchability can result from very small quantities (1 - 20 microlitres) of very toxic oils. Either the aromatic hydrocarbon or the non-hydrocarbon fractions of the oil may be responsible for such toxicity. (P14.1.w7).
    • Oil may be transferred to eggs from contaminated plumage during incubation. Oil in the environment may contaminate nesting sites and thereby contaminate eggs. (P24.327.w4)
  • Both crude and refined oils may have teratogenic effects on bird embryos resulting in growth retardation, bill deformation, incomplete skull ossification, skeletal deformities and other deformities. (P14.1.w7)
  • PAH compounds have been shown to be responsible for toxic effects of petroleum oils observed causing mortality of avian embryos. (B20.13.w10)
  • Different petroleum products may cause different levels of embryo mortality and reduced hatchability. (P14.2.w6)
  • High levels of bird embryo mortality may be seen following application of very small quantities of oil to the egg shell. The quantities required for such effects would easily be transferred from the plumage of adults during incubation. (B20.13.w10, P14.2.w6)
  • Avian embryos dying after the egg is oiled sometimes, but not always, show developmental defects. (P14.2.w6)
  • Pathological findings in embryos from oil-exposed eggs have included generalised oedema, liver necrosis, kidney degeneration, kidney necrosis and mineralisation and enlargement of the heart, liver and spleen. (P14.2.w6, P14.3.w16)
  • Paraffin (a petroleum product composed of large alkanes) applied to eggs did not affect hatchability or embryo survival, nor did propylene glycol. (P14.2.w6)
    • 50 L propylene glycol applied to mallard (Anas platyrhynchos) eggs at eight days of incubation did not cause reduced hatchability. This amount of propylene glycol would cover about 13% of the egg surface. (J40.42.w1)
    • 50 L paraffin applied to mallard (Anas platyrhynchos) eggs at eight days of incubation did not cause reduced hatchability. (J40.42.w1)
  • Various petroleum oils (South Louisiana crude, Kuwait crude, No. 2 fuel oil) all caused significant reductions in hatchability when applied to Anas platyrhynchos - Mallard eggs at eight days of incubation. Application of even 1 L of these oils reduced survivability of embryos to 70-82 % by 96 hours after application and hatching success was reduced to 62-72%. Greater volumes of oil resulted in higher 96-hour mortality and in lower hatching success; with 20 L embryo survival at 96 hours was reduced to 6%, 20% and 2% respectively and hatching success to 0, 6 and 0%. With application of 50 L of South Louisiana crude, no embryos survived even 96 hours. It was noted that the reduced survival could not be accounted for by reduced air exchange. It was noted that most mortality occurred within 96 hours of the application of oil, and that the toxicity was probably due to the aromatic rather than the aliphatic oil components. Hatched (i.e., surviving) ducklings did not show any gross abnormalities, nor did they have lower hatching weights than controls. (J40.42.w1)
  • Weathering was shown to decrease toxicity of oils (Prudhoe Bay crude oil, No. 2 fuel oil) to mallard eggs, with significant reduction in toxicity by two to three weeks of weathering, although some toxicity still remained following weathering, as indicated by reduced survivability of embryos from treated eggs, compared to controls. Oil killed rapidly: more than 80% of embryos dying after application of oil died within six days of the application. Surviving ducklings showed normal hatching weights. (J40.44.w1)
  • A single application of medicinal mineral oil at 2.0 to 35.9 mg per Anas platyrhynchos - Mallard egg, wiped thinly over the shell after six days of incubation, was sufficient to kill about 50% of embryos within two days; only five of 24 treated eggs hatched and all but one of these had been treated with less than 12 mg of oil. (J40.29.w2)
  • Application of four to five ml of medicinal mineral oil to the breast feathers of mallard ducks after eight days of incubation was sufficient that none of the eggs being incubated by the ducks hatched. (J40.29.w2)
  • A single dose of No. 2 fuel oil (10, 20, 50 or 100 L) was applied to the eggs of gulls (Larus marinus and Larus argentatus) during natural incubation. Survival of embryos was inversely proportional to the quantity of oil applied to the egg, and was affected by the age of the eggs at the time of treatment: significant reductions were seen with eggs treated with 10 or 20 L of oil at four to eight days after laying, while eggs which were more than half way through the 28 day incubation period at the time of oil application did not show reduced hatchability even with 100 L oil. Outdoor weathering of the oil for several weeks prior to application to the eggs did not reduce toxicity to the embryos. It was considered that oiling of eggs from pollution of adults was only likely to have a significant impact on populations of these species if severe oiling occurred early in incubation. However, it was noted that larger population effects might occur with species with lower reproductive potential and higher postfledging mortality, or greater sensitivity to oil, or subject to other stresses. (J50.101.w1)
  • Chicks surviving oiling initially may still show increased mortality during hatching. (P14.2.w6, P14.3.w16)
  • The precise toxic effect which causes hatching failure despite survival of the embryo following oiling, is unknown. (P14.3.w16)

Effects of oil on reproductive cycles and activity of adult birds:

  • Oil may have long-term effects on reproduction. (B334.w3)
  • Reproductive tract damage may occur. (B20.13.w10)
  • Ingested oil has been shown to result in decreased egg laying, decreased fertility and decreased hatching rates. (B20.13.w10)
    • Oestrogen cycles may be disrupted leading to reduced laying and fertilisation. (B20.13.w10, P24.335.w11)
    • Prolactin cycles may be disrupted leading to failure to incubate properly. (B20.13.w10, P24.335.w11)
    • Abnormal yolk structure has been reported, associated with reduced hatchability. (B20.13.w10)
    • A single oral dose of 500 mg No. 2 fuel oil to quail Coturnix coturnix japonica (Coturnix japonica - Coturnix - (Genus)) caused cessation of egg production for six to eight days; the same dose of bunker C oil caused cessation of egg production for the whole two week trial period. 200 mg bunker C oil, but not 100 mg, caused a reduction in egg production. Neither safflower oil at 500 mg nor mineral oil at 500 mg had any effect on egg production. Hatchability of eggs was markedly reduced for eggs laid on the first or second days after 200 mg bunker C oil. Yolk deposition in eggs laid after dosing with 200 mg bunker C oil was uneven and distinctly abnormal; lesser abnormalities were noted with a dose of 100 mg bunker C oil. In chickens 500 mg oil resulted in structural abnormalities in egg yolks and 3g caused egg production to cease. In Canada geese dosed with 2.0, 3.0 or 5.0 g of bunker C oil yolk abnormalities were noted. (J22.195.w1)
  • Laying mallards fed crude oil showed alterations in oestrus cycles. (P14.2.w6)
  • Plasma prolactin levels in breeding female ducks have been shown to be disrupted by oil. (P14.2.w6)
  • Failure of normal incubation behaviour has been demonstrated in breeding female ducks fed oil. (P14.2.w6)
  • Ingestion of oil may cause temporary abandonment of chicks, which may be lethal to recently-hatched chicks. (P14.2.w6)
  • Anas platyrhynchos - Mallard fed a diet contaminated with oil showed reductions in oviposition rates, egg fertilisation and hatchability. With 1 ml Kuwait crude oil per 100 g dry food no effect was observed. With 3 ml per 100 g dry food, oviposition was abolished; subsequent reduction to 1 ml/100g food restored a normal rate of oviposition, but reduced fertilisation was noted and none of the fertilised eggs produced viable ducklings. Egg shell thickness was not affected. With South Louisiana crude oil, ducks fed 3 ml per 100 g dry food showed significant declines in oviposition with fertilisation under 25% and hatchability of fertilised eggs only 40%; 1 ml per 100 g dry food did not affect oviposition rate but none of the eggs were fertilised. Additionally, a 33% decrease in egg shell thickness was noted with 3 ml of this oil per 100 g dry food. (J206.54.w1)
  • Ducks (Anas platyrhynchos - Mallard and Pekin (Anas platyrhynchus domesticus - Domestic Duck)) in lay, fed 2 g lubricating oil by stomach tube, ceased laying immediately and did not resume for two weeks; reproductive behaviour was also reduced. This amount would be ingested in the first three days after contamination of the plumage with about 6 g of oil. (J40.29.w2)
  • Cassin's auklets (Ptychoramphus aleuticus) were dosed with 300, 600 or 1,000 mg bunker C fuel oil, or 1,000 Prudhoe Bay crude oil, in gelatin capsules. The proportion of birds laying eggs significantly decreased in birds fed 1,000 mg of either oil, and, of eggs laid, significantly lower percentages hatched in those birds given 600 mg or 1,000 mg of bunker C oil. Hatching success was not affected in the birds given 1,000 mg of Prudhoe Bay crude oil. Post-hatching development of the chicks was not affected. Decreased egg laying occurred in the period nine to 13 days after dosing; given eight days of rapid formation of yolk and 4-5 days from the end of yolk formation to laying, this indicated that the oil was affecting yolk deposition in these birds. (J313.12.w1)
  • When female Coturnix coturnix japonensis - Japanese quail (Coturnix japonensis - Japanese quail (Coturnix - (Genus)) in lay were dosed with various petroleum oils, obvious changes in laying, egg yolk development and hatchability of eggs were noted. Dosing with 500 mg of No. 2 fuel oil halted production of eggs for six to eight days while 500 mg of bunker C oil halted egg production for at least 14 days. With 200 mg bunker C oil egg production was decreased on days one and two (P<0.001) and hatchability of eggs laid on these days was also markedly reduced (P<0.001) but hatchability had returned to normal by day four, while with 100 mg there was no apparent effect on the number of eggs produced. Structural abnormalities were noted in eggs laid after oil dosing (bunker C, 40% aromatic No. 2 fuel oil, Kuwait crude or south Louisiana crude); yolk deposition was uneven in the first few hours after dosing with petroleum oil. Thin, easily-cracked shells sometimes occurred in eggs from the birds fed oil. Similar effects were noted in chickens (Gallus gallus - Red junglefowl) fed oil: those fed 3 g bunker C oil ceased egg production; those fed 500 mg bunker C oil showed structural alterations in the yolk of eggs. Structural alterations in the yolk were also seen in eggs from Branta canadensis - Canada goose fed 2-5 g bunker C oil. (J22.195.w1)
  • A study of Spheniscus magellanicus - Magellanic penguin in Argentina noted a scarcity of oiled penguins at a nesting colony, compared to the number at non-breeding sites where the penguins were found. It was suggested that the discrepancy indicated that oiled penguins, even if they could survive while oiled, are not fit to breed. (J313.14.w1)

On mammals:

  • Mammals ingesting low levels of petroleum products could show reduced reproductive success. ((P9.1.w5))
  • In female Mustela vison - American mink experimentally exposed to oil, while individuals exposed acutely (by being placed in a slick of the oil on sea water) to either Prudhoe Bay crude oil or bunker C fuel oil showed no reproductive effects, females given either of the oils in feed at 500 ppm (a low contamination level) from sixty days prior to breeding until weaning, showed reductions in percentage whelping (76.2% of those given Prudhoe Bay crude oil and 25.0% of those given Bunker C fuel oil) and reduced number of liveborn kits per female bred (2.4 and 0.7 kits/female, respectively). No behavioural changes (eating, grooming or breeding) were seen with this level of oil ingestion. (P9.1.w5)

On reptiles:

  • Exposure of turtle eggs to oil-contaminated sand has been shown to result in death or abnormal development of turtle embryos. (P14.2.w1)
    • Fresh oil was more harmful than weathered oil. (P14.2.w1)
Teratogenic effects --
Mutagenic effects --
Carcinogenic effects


Organ toxicity --
Bird Toxicity --
Aquatic organism activity "Marine organisms show selective uptake of aliphatic and aromatic hydrocarbons." (J68.297.w1)
  • Principle enzymatic degradation pathways include oxidation of alkanes to fatty acids, hydroxylation of aromatic rings via epoxide intermediates, and oxydation of alkyl side-chain substituents on aromatic rings. (J68.297.w1) 
    • Chronic exposure to petroleum and other organic pollutants leads to induction of these enzymatic pathways, therefore previous history of exposure affects metabolism. (J68.297.w1)
    • The presence of, or previous exposure to, certain compounds, may affect the metabolic routes used in the breakdown of other products. (J68.297.w1)


  • Oil spills commonly result in the death or temporary debilitation of invertebrate organisms in the water column, littoral zone, and in or on sediments. (P14.2.w1)
  • Mortality and sublethal effects are caused by smothering as well as contact with dissolved or suspended oil, ingestion of oil or oil-contaminated food and water, and possibly also by chemical changes to the water such as pH change and oxygen depletion. (P14.2.w1)
  • Molluscs show both immediate mortality and longer term reductions in growth rate and survival. (J68.297.w2)
  • Chemical stress from petroleum might also exacerbate effects due to pathological microorganisms. (J68.297.w2)


  • Fish species vary in their sensitivity to petroleum oils. 
    • For Salmo clarki - Cutthroat trout, a concentration of petroleum oil in water of just 0.5 ppm can be lethal. (P14.2.w1
  • Mortality is highest in eggs and larvae in surface water and in early juveniles, particularly those in shallow water subjected to a heavy layer of oil on the water surface. (P14.2.w1)
    • Deaths of eggs, and deformed embryos, may result from exposure to oil. (J68.297.w2)
    • Gross abnormalities detected in embryos and larvae exposed to petroleum include jaw malformations, vertebral column flexures, reduced embryonic heart rate, loss of coordination and equilibrium and neurosensory cell degeneration. (J68.297.w2)
    •  Chromasomal and cytological abnormalities in developing planktonic fish have been shown in one extensive study to have a statistical association with surface water contamination, including petroleum contamination. (J68.297.w2)
  • Adults and juveniles in shallow waters are also at risk of exposure to dispersed or dissolved oil. (W469.Oct03.w2)
  • Sublethal effects include heart rate alterations, respiratory rate alterations, liver enlargement, growth reduction, fin erosion, various cellular and biochemical changes and behavioural responses. (P14.2.w1)
  • Neurosensory and integumental lesions commonly result from petroleum; increasing concentrations cause increasing tissue damage. (J68.297.w2)
  • Fin erosion has been documented in association with petroleum exposure on a number of occasions in the field, and has also been shown to be produced following experimental exposure of fish (Mugil cephalus - mullet) to oil. (J68.297.w2) 
    • Signs of fin erosion include epidermal hyperplasia, dermal fibrosis, hyperaemia and occasionally haemorrhage. There is no pronounced inflammatory response and no consistent bacterial infection. (J68.297.w2)
    • Bacterial (Vibrio sp.) infection was found to be involved in experimental oil-associated fin erosion in Mugil cephalus - mullet. Chemical stress from the petroleum, together with an altered microbial flora favouring Vibrio, were thought to be responsible for the disease condition described. (J68.297.w2)
  • Hepatic effects in fish (Parophrys vetulus - English sole) experimentally exposed to oiled sediments were pronounced, with severe hepatocellular lipid vacuolation (up to 95% of the cell volume consisting of lipid droplets and vacuoles) together with extensive proliferation of the rough endoplasmic reticulum. Continuously oiled fish lost weight, while haematocrits and haemoglobin levels increased. Effects declined "markedly" after the first month. (J68.297.w2)
  • Pathological effects are known to occur associated with polycyclic aromatic hydrocarbons (PAH). Exposure of Fundulus heteroclitus, a euryhaline fish, to the PAH naphthalene (concentrations of 0.002-30 mg/L for up to 15 days) resulted in necrosis of neurosensory cells (with concentrations as low as 0.02 mg/L), brain, lever and pancreas lesions (with concentrations as low as 0.2 mg/L), blood stasis (with higher concentrations), necrosis of gut mucosa and degeneration of skeletal muscle with the highest concentrations, and general signs of chemical stress, such as gill hyperplasia and haemorrhage, with all tested concentrations. It was noted that naphthalene was selectively accumulated in the organs in which pathology was most evident. (J68.297.w2)
  • Sloughing of gill epithelium, liver pathology (increased rough endoplasmic reticulum), splenic discolouration and intestinal lesions have been described associated with exposure of various fish species to different types of petroleum. (J68.297.w2)
  • Note: many observed pathological effects represent classical responses of cells and tissue to toxic irritants, and are general responses to chemical stressors, rather than specific responses to oil. (J68.297.w2)
Other organism toxicity Vegetation
  • Petroleum products adversely affect a wide variety of plants. (P14.2.w1)
  • Oil spills have been recorded to cause the death of mangroves, seagrasses and large intertidal algae, with severe effects on salt marsh vegetation, lasting for more than two years and destruction of vegetation of freshwater wetlands. (P14.2.w1)
  • Mangroves have complex breathing roots which are above the surface of the muds, organically rich but oxygen-depleted, in which they live. Oil may block the openings of these air breathing roots and may interfere with the salt balance of the trees, causing leaves to drop and death of the plants. Root systems may be damaged also by fresh oil entering animal burrows nearby. The effect of oil on mangrove swamps may persist for some time inhibiting recolonisation by seedling mangroves. (W469.Oct03.w2)
  • Recovery times for local plant populations varies. For mangrove forests, ten to 15 years may be required for recovery. For most other habitats a few weeks to five years is likely. (P14.2.w1)
  • Factors affecting recovery times include the type of petroleum product involved, the circumstances of the spill, the plant species affected and clean-up actions utilised, which can actually be detrimental (e.g. mechanical recovery of oil in wetlands may increase time to recovery by 25-50%). (P14.2.w1)
  • Oiling is more likely to be lethal to plants if the lower parts of the plants and their root systems are affected; coating of leaves may be less important, particularly if it occurs outside the growing season. (W469.Oct03.w2)

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Nutrient Information

Nutritional Data
Sources --
Biological Use --
Recommended Daily Allowance / Recommended level in food --
Stability in food (Storage time) --
Interactions --

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External / Environmental Information

External / Environmental Uses
Use --
Formulation --
Application method --
Application Concentration --
Persistence of Effect / Frequency of Application --

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Sources in the Environment
Natural sources
  • Marine seeps. (B368.1.w1, P24.335.w11)
  • Onshore seeps (J68.297.w1) (sediment erosion) (B368.1.w1)

    • Exposed bituminous shales; erosion of oil-bearing rocks. (J68.297.w1, P24.335.w11)
  • Note: These sources represent about 7.8% of oil entering the environment annually. (P24.335.w11)
Human-associated sources
  • A 1985 report estimated a yearly spillage into the environment of two to nine million metric tonnes of crude oil and petroleum products, including about 15% from oil spills, 33% from "routine shipping operations" and 8% from industrial and municipal effluents. (B20.13.w10) 
  • Marine transport: tanker operations, dry-docking, marine terminals, bilge and fuel oils, leaks from poorly maintained vessels, irresponsible dumping, accidents involving tankers or other vessels, seepage from sunken vessels. (B368.1.w1, J68.297.w1, P24.335.w11)
    • Oil spills are most common in areas with traffic of oil tankers or other large ships as well as locations with oil wells, oil pipelines or oil refineries. (B20.13.w10)
    • Handling losses at shore terminals are estimated at 0.00008-0.00015% of total oil movement at storage depots and terminals. (J68.297.w1)
  • Discharges from ballast and tank-washing water result in more oil in the environment than do accidents involving oil tankers. (B368.1.w1, P24.335.w11)
    • Discharges of these types are regulated by the International Maritime Organisation. (P24.335.w11)
      • Discharges from the cargo areas of tankers are allowed in international waters at a rate of not more than 60 L/mile and not exceeding 1/15,000 of the cargo (older tankers) or 1/30,000 of the cargo (newer tankers). Such discharges are prohibited within territorial waters and in designated areas such as the Mediterranean and the Red Sea. (P24.335.w11)
      • Ballast water carried in cargo tanks, and thereby contaminated with oil, legally can be discharged only to onshore treatment facilities where the oil is separated from the water before the water is discharged. (P24.335.w11)
        • Such water still contains particulate oil and volatile hydrocarbons. (P24.335.w11)
  • Offshore oil activity.
    • Oil may be released in formation and production water, displacement water, accidental spills, platform runoff and from drill cuttings. (B368.1.w1, J68.297.w1)

    • Offshore oil production can be a major source of spilled oil. (B368.1.w1)
  • Scattered petroleum releases occur at outfalls of water treatment plants, storm drains, in rivers and in streams. (B20.13.w10, J68.297.w1)
  • About 0.02% of oil reaching the marine environment comes from offshore oil exploration and production. (P24.335.w11)
    • Both drilling muds (water-based and oil-based) and produced water may contain oil. (P24.335.w11)
  • Pipeline ruptures. (P24.335.w11)
  • Storage tank ruptures and overflows. (P24.335.w11)
  • Truck and rail accidents. (P24.335.w11)
  • Industrial wastes from refineries and other industries, urban runoff, river run-off and ocean dumping. (P24.335.w11)
    • Oil may be present in sewage effluent entering tidal waters, sewage sludge dumped at sea, industrial effluent and industrial waste dumped at sea. (J68.297.w1)
    • Refineries discharge effluents to tidal waters; losses are greater from older refineries. (J68.297.w1)
    • Municipal wastes, refineries, nonrefining industrial wastes, urban runoff, river runoff, ocean dumping. (B368.1.w1)
N.B. Food items contaminated with oil (e.g. bivalves which act as a food source for birds and other species) may remain as a source of oil for other organisms for years after the original release of oil into the environment. (B36.42.w42)

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Effects on the Environment
Effects in the aquatic environment

The effects of oil will depend on both when and where a spill occurs. (B20.13.w10)

  • Negative impacts on mammals and birds may be most severe when a spill occurs near to shore at a time when large numbers of birds or mammals are present in an area. B20.13.w10)
  • Negative impacts on other aquatic organisms may be most severe if the spill occurs in a particularly sensitive area. (B20.13.w10)
  • Because oil remains on the surface for prolonged periods at high concentration species which live on or pass through the water surface are exposed to high concentrations of oil. (B20.13.w10, W469.Oct03.w2)
  • Species which live in the water and bottom-dwelling species become exposed as oil is redistributed into water and sediments. (B20.13.w10)
  • Persistent spilled oil residues and oil mousse can contaminate and physically smother organisms, including both animals and plants. (W469.Oct03.w2)
  • Lethal toxic components tend to be present for a relatively short time as the most toxic components are also those which are rapidly lost by evaporation. (W469.Oct03.w2)
  • Sub-lethal toxic effects of oil, which may be due to prolonged exposure to sub-lethal concentrations of oil or oil components, may impair reproduction, growth, feeding etc. (W469.Oct03.w2)
    • Oil components are particularly likely to be concentrated by filter-feeding sedentary animals in shallow waters, such as mussels, clams and oysters. (W469.Oct03.w2)
Effects on land The effects of oil which comes ashore will depend on the type of shore (e.g. rocky, sandy) and the plant and animal communities there. (W469.Oct03.w2)
  • Salt marsh and mangroves are particularly vulnerable to the effects of oil. (W469.Oct03.w2)
N.B. The effects of heavy clean-up machinery may be more detrimental in some habitats that the effects of the oil. (W469.Oct03.w2)

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Persistence in the Environment
Breakdown in soil and groundwater


  • The time taken for petroleum products deposited on land to break down depends on the characteristics of the land on which it is deposited. (P14.2.w1)
  • Oil may be retained for as short a period as a few days on rock cliffs or as long as ten years or more in sheltered tidal flats and wetlands. (P14.2.w1)
    • Oil will persist longer on shore in cold conditions with ice, low wave energy and decreased chemical and biological degradation. (P14.2.w1)
  • Oil retained in sediments and shorelines can act as a persistent, chronic source of oil released into nearshore waters. (P14.2.w1)
  • Oil spilled directly onto land is degraded by evaporation, photo-oxidation and microbial action. (P14.2.w1)
  • It should be noted that oil spilled on lakes and streams is likely to have less time to weather before coming ashore than that which is spilled at sea. (P14.2.w1)
Breakdown in water The main processes of redistribution and degradation of oil include "evaporation, photooxidation, dispersion, dissolution, biodegradation and sedimentation." (J68.297.w1)

Ageing or weathering of petroleum products:

  • "Weathering" refers to the process which occurs after oil has been released into the environment.(P14.3.w12, W469.Oct03.w1)
  • Weathering "includes spreading, evaporation, dissolution, dispersion into the water column, photochemical oxidation, formation of emulsions, microbial degradation, adsorption to suspended particulate matter, stranding on shore, or sedimentation to the sea floor. Weathering changes the physical and chemical properties of spilled oil and thereby influences its toxicity to marine organisms." (B368.1.w1)
  • Weathering generally takes about a year. It is fastest initially and slowest later. (B20.13.w10, P24.335.w11)
  • In the water column, petroleum products generally persist for no more than six months. ( B36.42.w42)
  • Light petroleum products such as kerosene are considered "non-persistent" as they tend to evaporate and dissipate quickly. (W469.Oct03.w1)
  • Heavier petroleum products, such as crude oils, show longer persistence. (W469.Oct03.w1)
  • Physical properties of the oil which affect its persistence include its density, viscosity and pour point. (W469.Oct03.w1)
  • Other factors affecting persistence include the amount of oil spilled and various environmental factors such as weather conditions and whether the oil remains on water or is washed ashore. (W469.Oct03.w1)
  • Petroleum products generally remain in the water column for less than six months unless spilled at high latitudes or just before winter in lower latitudes. (P14.2.w1)
    • Oil trapped under ice may remain there essentially unchanged until the following spring. (P14.2.w1)
  • Both the physical and chemical properties of petroleum oils are affected by weathering. (P24.335.w11)
  • After being spilled into the environment, oil undergoes "weathering" involving a series of changes in both chemical composition and physical properties. Processes occurring during weathering include evaporation of volatile components, dissolution, photochemical oxidation, biological degradation, formation of emulsions with water, either oil-in-water emulsion or the water-in-oil emulsion known as "mousse", physical spreading of the oil, retraction due to polymerisation, and sedimentation.(B20.13.w10)
  • Weathering includes spreading, evaporation, dissolution, dispersion of oil into the water column, photochemical oxidation, formation of emulsions, microbial degradation of oil, adsorption onto suspended particulate matter, sedimentation to the ocean floor and deposition on shore. (P24.335.w11)
  • During weathering, lighter, volatile components may be lost relatively quickly, with subsequent relative increase in concentration of compounds higher in molecular weight. (P14.3.w12)
    • In general, loss of volatile components will occur in four to 36 hours after the spill has occurred. (P14.3.w12)
    • Loss of volatile components may be reduced if these compounds are trapped under a crust or if they have been preferentially "wicked" into feathers and thus retained on oiled birds. (P14.3.w12)
    • Weathering removes low molecular weight compounds; the remaining oil is enriched in higher molecular weight, more complex saturates, naphtheno-aromatics, PAHs, resins and asphaltanes. (B368.1.w1)
  • Oil commonly becomes broken up into smaller units.(B20.13.w10)
  • At the end of the weathering process, which may on average take about one year, the remaining oil is present as pancake-shaped patches or "tar balls": polymerised masses of compounds of high molecular weight. These come ashore or break into small pieces and fall to the bottom; they may persist in the environment long term. (B20.13.w10, P14.2.w1)
  • The process of weathering generally takes place faster at higher temperatures and more slowly at lower temperatures, especially under ice, while oil trapped in sediments may not become weathered. (B20.13.w10)


  • Oil, which is lighter than water, floats on the surface of the water as an oil slick. (P24.335.w11)
  • If oil is released below the surface of the water it must rise through the water before it can form a slick. (B368.1.w1, P24.335.w11)
    • Oil released below the water surface may form into droplets before reaching the surface, in which case no slick will form. (P24.335.w11) Oil droplets may form and disperse. (B368.1.w1)
    • Compounds of lower molecular weight dissolve. (B368.1.w1)
  • Oil on the water surface spreads horizontally. (P24.335.w11)
  • Spreading of oil is affected by the physical and chemical properties of the oil/oil product, the amount of oil, and on both how and where it is spilt. (J68.297.w1)
  • The slick becomes orientated in a direction determined by the wind, tide, water movements and currents and drifts due to these forces. (P14.2.w1, P24.335.w11)
    • Near coasts, it is necessary to consider local winds and tides in determining the likely direction of slick spreading. (J68.297.w1)
    • The centre of the slick mass may move at about 3% of wind speed, plus a 20-30 degree shift to the right (northern hemisphere) due to the Coriolis effect. (B368.1.w1)
  • The rate of spread of oil is also affected by wind speed, currents, tidal streams and temperature.(B368.1.w1, W469.Oct03.w1)
    • Spreading occurs faster on warm than on cold water (B368.1.w1)
    • Spreading is increased by moderate wave action. (B368.1.w1)
    • The slick lengthens at a linear rate with time; the width increases as a function of t0.5.(B368.1.w1)
  • Slicks generally break up from an initial single sheet into narrow bands or windrows which are parallel to the direction of the wind. (W469.Oct03.w1)
  • Heavy oils and weathered oils may sink and move either below the surface or along the bottom of the water body, in a direction determined by water currents and tides. (P14.2.w1)
  • The thickness of the oil layer may vary from micrometres to centimetres. (P14.2.w1)
  • Oil spreads faster if it is released into the water faster. (P24.335.w11)
  • Low viscosity oils, particularly in warm water, spread further and faster than do high viscosity oils. (P24.335.w11, W469.Oct03.w1)
  • Slicks typically are variable in thickness. (W469.Oct03.w1)
    • Crude oils and heavy distillates form two phases with a thin sheen (0.01-0.001 mm thick) surrounding the thick phase which may be 1.0 to 20 mm thick. (P24.335.w11)
    • As the thick phase weathers it breaks up into patches and moves faster than does the sheen, which is left behind. (P24.335.w11)
  • The rate at which oil spreads decreases with time. (P24.335.w11)
    • Spreading of oil takes place mainly in the first day following a spill, although some spreading may continue for a week or longer. (J68.297.w1)

Spreading on rivers:

  • On rivers, flow, and oil movement, is in one direction, downstream. (D164.3.w3)
  • Significant amounts of oil, particularly relatively dense oil, or oil finely distributed as droplets, can be mixed and dispersed subsurface due to interaction of shear in currents along the river bottom and banks, and turbulence. (D164.3.w3)
  • Because the surface and centre of a river move faster than the water along the bottom and banks, oil can become "smeared", with patches moving towards the banks and later returning to the main flow a distance behind the main patch. (D164.3.w3)
  • Artificial structures designed to control sediment migration within navigation channels, and to avoid excess buildup of silt by maintaining current velocities, may also produce artificial side bays in which floating pollutants, such as oil, will accumulate (and where cleanup/recovery may therefore be required). (D164.3.w3)
  • Overflow weirs tend to mix oil into water downstream as the water plunges over the dam. (D164.3.w3)
  • Sluice gates tend to restrict oil upstream of the gates, acting like a boom, unless the flow through the gates is fast (more than about a knot), in which case the oil will not be stopped. (D164.3.w3)
  • The main forces determining oil distribution are currents and shear, although wind will also act in a minor way to determine which bank of the river the oil tends towards. (D164.3.w3)


  • Evaporation is a major process of weathering in the first few days after oil has been spilled. (B368.1.w1, P24.335.w11)
  • The evaporation rate is affected by the type of oil, the surface area of the slick, and environmental conditions. (B368.1.w1, P24.335.w11, W469.Oct03.w1)
    • Evaporation of a given substance is directly proportional to its vapour pressure and inversely proportional to its molecular weight. Vapour pressure is inversely proportional to temperature, therefore evaporation is reduced in cold conditions. (B368.1.w1, P24.335.w11)
  • Oil compounds of low molecular weight readily evaporate. (P14.2.w1, J68.297.w1, W469.Oct03.w1)
  • Evaporation mainly occurs within the first hundred hours after a spill. (J68.297.w1) 
    • Evaporation is faster if the ambient temperature and water temperature are high. (P24.335.w11)
    • In temperate conditions components with a boiling point under 200 C tend to evaporate within the first 24 hours. (W469.Oct03.w1)
    • Light oils, including petrol (gasoline), kerosene and aviation fuel may evaporate practically completely within a few days. (B368.1.w1, P24.335.w11, W469.Oct03.w1)
    • As much as 60% to 75% of light crude oils and some refined products such as No. 2 fuel oil and gasoline may evaporate over a period of a week. (B368.1.w1, P14.2.w1, P24.335.w11)
    • Experimentally, 35% by mass of a thin Forties crude oil slick on seawater in open outdoor tanks was lost be evaporation over 24 hours, while about 25% of a Kuwait crude was lost under "average English Channel conditions", and in sea trials about 50% of crude oil added to the sea surface was lost be evaporation. In a controlled ecosystem "approximating to a temperate estuarine environment", 80-90% of the exponential loss of diesel oil over 90 hours was by evaporation. (J68.297.w1)
    • As the oil spreads, a larger area is exposed and evaporation can increase. (W469.Oct03.w1)
    • The evaporation rate tends to increase with higher temperatures and in high wind speed and rough sea conditions. (W469.Oct03.w1)
  • As evaporation removes volatile components the density of the remaining oil increases while vapour pressure and toxicity are reduced. (P24.335.w11)
    • The rate of diffusion of remaining volatile hydrocarbons is reduced as water-in-oil emulsions and tar balls and mats develop. These (emulsions, tar balls, tar mats) may develop a crust of mainly nonvolatile oil components, with a covered core of less weathered oil containing higher concentration of lighter molecular weight hydrocarbons. (B368.1.w1)
  • Note: oil components lost to the atmosphere either as gas or in aerosols may then undergo oxidative or photooxidative reactions, and may become adsorbed onto particles. However these reactions have not been closely studies and their nature and extent are unknown. (J68.297.w1)


  • Water soluble components of the oil become dissolved in the water. (P24.335.w11, W469.Oct03.w1)
    • This is one of the ways in which oil enters the water column (the others being by formation of emulsions, and by adsorption onto particles. (J68.297.w1)
    • Dissolution of oil in water depends on the composition and state of the oil. (W469.Oct03.w1)
    • Less than 5% of either crude oil or refined petroleum products will dissolve in water. (P14.2.w1) Less than 2-5% of spilled oil will be removed by dissolution. (B368.1.w1)
    • Oil which is more finely dispersed in the water will dissolve more quickly. (W469.Oct03.w1)
    • Light aromatic compounds such as benzene and toluene are the most soluble in water; these compounds tend to evaporate at a rate 10-100 times faster than dissolution. (W469.Oct03.w1). 
  • Dissolution brings highly toxic hydrocarbons into contact with marine organisms in a form which is readily available to the organisms. (P24.335.w11)
  • Dissolved hydrocarbon compounds can persist in the water; they may be found a few kilometers distant from the site of the spill. (P24.335.w11)
  • This is one of the first stages of weathering, but removes only about 2.0-5.0% of the total oil. (P24.335.w11)



  • Dispersion of oil occurs due to the turbulent action of waves, which causes oil droplets to break off from the main body of the oil slick. (P24.335.w11, W469.Oct03.w1)
  • Dispersion occurs more quickly with light low viscosity oils. (W469.Oct03.w1)
  • Dispersion occurs more rapidly in rough water conditions. (P24.335.w11, W469.Oct03.w1)
  • Large droplets of oil tend to coalesce, rise, and concentrate near the surface of the water, or spread out in a thin surface film. (B368.1.w1, P24.335.w11, W469.Oct03.w1)
  • Small oil droplets (less than 0.1 mm diameter) become dispersed in the water column. (B368.1.w1, P24.335.w11, W469.Oct03.w1)
  • Dispersion begins early after oil spillage and peaks within 10 hours; within 100 hours it overtakes spreading as the main mechanism of movement of oil from the site of the spill. (B368.1.w1)
  • Dispersion is the most important process by which oil slicks break up and disappear. (P24.335.w11)
  • Dispersion provides a greater surface area of oil in contact with the water which encourages dissolution, biodegradation and sedimentation of the oil. (W469.Oct03.w1)
  • The rate of oil dispersion is affected by wave action, wind action, oil viscosity and the presence of natural surfactants which facilitate formation of droplets and inhibit coalescence. (B368.1.w1, P24.335.w11)
  • If artificial dispersants are introduced then the amount of oil dispersed in the water column, and eventually settling out, can be substantially increased. (J68.297.w1)


  • Two forms of emulsion, the suspension of one liquid in another, can form between oil and water: oil-in-water or water-in oil. (P24.335.w11, W469.Oct03.w1)
  • Oil-in-water emulsion disperses increasingly with time. (P14.2.w1)
  • Water-in-oil emulsion, sometimes called "chocolate mousse" because it is frothy and brown, is formed by wind and wave action.(P24.335.w11, W469.Oct03.w1)
  • Water-in-oil emulsion is stable, may contain up to 75% water, can be four times the volume of the original oil and is more viscous than the original oil. (B368.1.w1, P24.335.w11, W469.Oct03.w1)
  • Mousse is stable and resists degradation; it may remain intact for months. (P14.2.w1)
  • Water-in-oil emulsion is more likely to form when the original oil is of relatively low viscosity.
  • Water-in-oil emulsion breaks down quickly in warm environments but is very persistent in cold waters, forming a stiff foam which may persist for long periods on water, on beaches or collected beneath sea ice.
  • Once a water-in-oil emulsion has formed evaporation and dissolution of the lighter fractions are inhibited, as are photochemical and microbial degradation of the heavier fractions. (B368.1.w1, P24.335.w11)
  • Dispersants are less effective at cleaning up such emulsions. (P24.335.w11)
  • Oils with an asphaltene content of greater than 0.5% are more likely to form a stable water-in-oil emulsion and this may persist for months. (W469.Oct03.w1) Oils with lower contents of asphaltenes are less likely to form a mousse and, if formed, it is more likely to disperse. (W469.Oct03.w1)
  • Under certain conditions, heating by sunlight in calm seas or once stranded on shore, the oil and water may separate again. (W469.Oct03.w1)


  • The main type of photodegradation of oil is photo-oxygenation, the chemical combination of oxygen with hydrocarbons to produce peroxides, aldehydes, ketones, acetones, alcohols and fatty acids. (B368.1.w1, P24.335.w11) High molecular weight byproducts, not soluble in oil or in water, are also formed. (B368.1.w1)
  • Products of photo-oxygenation are polar (B368.1.w1, P14.2.w1) and more water-soluble than the original hydrocarbons and also more toxic. (P24.335.w11)
    • Oxidation occurs more readily if the oil is heavy in metals or sulphur. (P14.2.w1)
  • High molecular weight byproducts of this process are released which are soluble in oil or water. (P24.335.w11)
  • Photo-oxidation is relatively slow. (P24.335.w11)
    • Typically less than 0.1% of a thin film of oil is broken down by photo-oxidation per day even in strong sunlight. (W469.Oct03.w1); 
    • 0.7% per day has been estimated from laboratory tests. (J68.297.w1)
  • Direct photolytic reactions also occur. 
    • These reactions do not require oxygen. (B368.1.w1, P24.335.w11)
    • These reactions increase with increasing molecular weight of the petroleum compounds, and with increasing light intensity. (B368.1.w1, P24.335.w11)
      • The tendency of polycyclic aromatic hydrocarbons (PAHs) to undergo direct photolysis increases with increasing molecular weight. (B368.1.w1)
    • Light intensity, and therefore direct photolysis, decreases at higher latitudes and with increasing depth of water. (B368.1.w1, P24.335.w11)
    • The rates of photolysis of some compounds are more sensitive to light intensity than others. (B368.1.w1, P24.335.w11)
  • Oxidation of high viscosity oils or emulsions results in the formation of tars. These may form an outer protective coating which results in longer persistence of the oil. (W469.Oct03.w1)
    • Tarballs, caused by this process, typically have a solid outer crust surrounding a softer interior which is less weathered. (W469.Oct03.w1)


  • Microbial degradation starts about one day after oil enters the water and persists as long as hydrocarbons remain. (B368.1.w1, P24.335.w11)
  • Microbes which degrade petroleum include bacteria, yeasts and filamentous fungi. (P14.2.w1, P24.335.w11)
  • Different microbes tend to degrade different groups of petroleum compounds. (W469.Oct03.w1)
  • Some petroleum compounds are relatively resistant to biodegradation. (W469.Oct03.w1)
  • Lower weight hydrocarbons are more readily broken down by microbial degradation than are compounds of higher mass and branching or substitution, such as resins and asphaltenes, which therefore remain in the environment. (J68.297.w1, P24.335.w11)
  • Microbes metabolise hydrocarbons to carbon dioxide and water. (P24.335.w11)
  • The rate of microbial degradation is affected by populations of petroleum-degrading organisms, oxygen concentration, temperature, presence of nutrients such as nitrogen and phosphorus, presence of organic carbon other than oil, salinity, the physical state of the oil, the chemical composition of the oil, water-sediment exchange processes, rate of bioperturbation, and whether there have been previous spills in the area. (B368.1.w1, J68.297.w1, P24.335.w11, W469.Oct03.w1)
    • Higher biodegradation rates occur in areas with previous exposure to oil. (J68.297.w1)
    • Higher biodegradation occurs near the surface of sediments than in lower layers, due to the requirement for aerobic conditions. (J68.297.w1)
    • Hydrocarbons buried in sediment may be remobilised to the surface of the sediment by diffusion in the pore waters, and may then be subject to biodegradation. (J68.297.w1)
    • Biodegrading organisms cannot use PAH as their sole carbon source; additional sources of organic carbon must be available. (J68.297.w1)
  • Because oxygen is required for biodegradation, this can occur at the oil-water interface but not within the body of the oil; it will occur faster if the oil is dispersed into droplets as these present a greater total surface area to the water. (W469.Oct03.w1)
  • Degradation rates are significantly lower at low temperatures. (B368.1.w1, P24.335.w11)
  • Degradation rates are slower in conditions of low light intensity. (P24.335.w11)
  • Bacteria capable of degrading hydrocarbons increase when exposed to petroleum oils. (P24.335.w11)
  • Microbial degradation occurs relatively slowly even in optimum conditions. (B368.1.w1, P24.335.w11)
  • Microbial degradation occurs both in the water column and on the bottom. (P14.2.w1)
  • Biodegradation is higher on coarse than fine sediments; this may be related to better aeration and higher subsurface nutrient concentrations. (J68.297.w1)
  • Other organisms may take up oil and metabolise it to a greater or lesser extent. Oil may be taken up by filter feeding plankton, bivalve molluscs, fish, birds and mammals. (P14.2.w1)

Sedimentation and sinking:

  • Some heavy refined petroleum products, with a density greater than one, will sink in fresh or brackish water; very few have a density higher than that of seawater (approximately 1.025) (B368.1.w1, W469.Oct03.w1)
    • Residues left after spilled oil has caught fire are sometimes sufficiently heavy to sink. (W469.Oct03.w1)
  • Sedimentation of oil occurs through:
    • Adsorption of oil droplets onto suspended particulate matter , especially clay but also other particles including zooplankton faecal pellets, phytoplankton, microbes and miscellaneous detritus, which then falls to the sea bed. (B368.1.w1, P14.2.w1, P24.335.w11)
    • Adsorption of oil onto beach sand, or erosion of hardened oil on substrates such as rocks, which is then washed out to sea by tides and deposited in the subtidal zone. (P24.335.w11)
    • Direct sinking of heavy or weathered oil. (P24.335.w11)
  • In water with a higher amount of suspended particulate matter more oil is absorbed and transported to the bottom. (P24.335.w11)
    • Shallow waters often contain large amounts of suspended solids, which provides a favourable condition for sedimentation of oil. (W469.Oct03.w1)
    • Sedimentation is most likely to be important in coastal and esturine waters with high turbidity, although it can also occur in the open sea. (J68.297.w1)
  • Penetration of oil into sediments depends on the sediment type and composition, with more penetration into coarse sediments than into fine unconsolidated sediments. High oil concentrations may be found in very fine, silt sediments, which have a large surface area. (J68.297.w1)
  • Sinking of oil is increased in water of lower density, such as fresh water. (P24.335.w11)
  • Oil may also be carried to the bottom with water sinking at the edge of ice sheets. (P24.335.w11)
  • Oil or mousse washed onto shores, such as sandy beaches, may mix with sediments such as sand and this mixture may then roll about in surf (J68.297.w1) and may sink if washed back out to sea. (W469.Oct03.w1)


  • Oil may strand either unweathered or at any stage of the weathering process. (J68.297.w1)
  • Residual oil or tar-balls on the water surface may eventually strand along coastlines. (J68.297.w1)
  • Stranded oil on sheltered rocky coasts, tidal flats and esturine marshes may remain, showing little overall degradation, for long periods. (J68.297.w1)
    • A crust may form on the surface of stranded oil, with oil under the crust then being protected and remaining unchanged. (J68.297.w1)
  • Stranded oil on exposed rocky coasts are likely to be cleaned by wave action etc. (J68.297.w1)
Breakdown in vegetation
  • Plants are killed or sublethally damaged by oil due to contact with oil or dissolved oil, systemic uptake of oil compounds, blockage of surface pores preventing air exchange and possibly also indirectly by effects of oil on soil and water causing physical and chemical changes such as oxygen and nitrogen depletion, change in pH and decreased penetration by light. (P14.2.w1)
  • Some microalgae have the ability to utilise oil as a food source. Activity of such oil-resistant species may be stimulated by the presence of petroleum products, while other microalgae will be inhibited. (P14.2.w1)
  • Large plants show death, reduced growth and impaired reproduction. (P14.2.w1)

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