c) Dissolution: Just as with evaporation, the dissolution of petroleum hydrocarbons
depends on the number of carbon atoms. Roughly speaking, 10 mg/l from a compound with 6 carbon atoms, 1 mg/l from a compound with 8 carbon atoms, and
0.01 mg/l from a compound with 12 carbon atoms dissolve in distilled water; solubility in seawater is somewhat less. The situation becomes, however, more complicated
when there is a complex mixture of different compounds which, as regards solubility,
have reciprocal effects. From American crude oil an amount of 46 mg/l dissolves in
seawater within 8 days, while the concentration derived from light fuel oil is only
7.5 mg/l after 5 days, and from heavy fuel oil, 2.3 mg/l (Benjamin and Polak 1973).
It has not been sufficiently explained to what extent it is a case of genuine dissolution and whether colloid micelle or adsorption to small particles plays the major
role.
When oil is decomposed under the action of ultraviolet sunrays by oxidation watersoluble fatty acids and fatty alcohols are produced which are easier for microorganisms to degrade than the original hydrocarbons.
d) Emulsification: When the seawater surface is agitated by wind, and especially
when foam and spray result, water is absorbed by the masses of oil. Some oils very
quickly absorbe more than 50% of their weight in water and form brown masses
dubbed "chocolate mousse". Within 7 h, North Sea oil absorbs up to 80% water.
Then the oil slick breaks up into little masses. Besides water-in-oil emulsions, oil-inwater emulsions (dispersions) form naturally or particularly under the influence of
added dispersion chemicals (dispersants). There, tiny drops of oil will be found floating around in the water.
On the whole, emulsification and dispersion are very effective means for reducing
large quantities of floating oil. Of course, oil is not eliminated from the marine
environment by emulisfication and dispersion; it is merely removed from the ocean
surface and distributed in the water mass where its poisonous effect persists.
e) Biodegradation: At least 90 strains of marine bacteria and fungi are capable of
biodegrading some components of petroleum. Some algae also have this ability. In
part, we are dealing with specialists that prefer to live off petroleum hydrocarbons.
They are generally found in the seawater of areas that regularly suffer oil pollution.
They are rare in other areas, fewer than 100 germs per liter of seawater, and they
increase only when the amount of petroleum hydrocarbons increases because of an
oil accident. In the North Sea, the number of oil-degrading bacteria is generally low,
and fairly large concentrations have only been found in the vicinity of the Ekofisk
and Forties oil-producing platforms (Oppenheimer et a1. 1977). Naturally, it takes
time after an oil spill until an optimal number of oil-decomposing bacteria is
present.
The efficiency of these bacteria depends on a number of environmental factors.
According to some experiments, at low temperature biodegradation is very slow. At
freezing point temperature, they only degrade around 10% of the amount they
would at 25°C. However, there are other experiments which indicate that sometimes
degradation at low temperatures is not much less than at warm temperatures. As a
rule petroleum alone does not contain enough nutrients like nitrogen and phosphorus
74
depends on the number of carbon atoms. Roughly speaking, 10 mg/l from a compound with 6 carbon atoms, 1 mg/l from a compound with 8 carbon atoms, and
0.01 mg/l from a compound with 12 carbon atoms dissolve in distilled water; solubility in seawater is somewhat less. The situation becomes, however, more complicated
when there is a complex mixture of different compounds which, as regards solubility,
have reciprocal effects. From American crude oil an amount of 46 mg/l dissolves in
seawater within 8 days, while the concentration derived from light fuel oil is only
7.5 mg/l after 5 days, and from heavy fuel oil, 2.3 mg/l (Benjamin and Polak 1973).
It has not been sufficiently explained to what extent it is a case of genuine dissolution and whether colloid micelle or adsorption to small particles plays the major
role.
When oil is decomposed under the action of ultraviolet sunrays by oxidation watersoluble fatty acids and fatty alcohols are produced which are easier for microorganisms to degrade than the original hydrocarbons.
d) Emulsification: When the seawater surface is agitated by wind, and especially
when foam and spray result, water is absorbed by the masses of oil. Some oils very
quickly absorbe more than 50% of their weight in water and form brown masses
dubbed "chocolate mousse". Within 7 h, North Sea oil absorbs up to 80% water.
Then the oil slick breaks up into little masses. Besides water-in-oil emulsions, oil-inwater emulsions (dispersions) form naturally or particularly under the influence of
added dispersion chemicals (dispersants). There, tiny drops of oil will be found floating around in the water.
On the whole, emulsification and dispersion are very effective means for reducing
large quantities of floating oil. Of course, oil is not eliminated from the marine
environment by emulisfication and dispersion; it is merely removed from the ocean
surface and distributed in the water mass where its poisonous effect persists.
e) Biodegradation: At least 90 strains of marine bacteria and fungi are capable of
biodegrading some components of petroleum. Some algae also have this ability. In
part, we are dealing with specialists that prefer to live off petroleum hydrocarbons.
They are generally found in the seawater of areas that regularly suffer oil pollution.
They are rare in other areas, fewer than 100 germs per liter of seawater, and they
increase only when the amount of petroleum hydrocarbons increases because of an
oil accident. In the North Sea, the number of oil-degrading bacteria is generally low,
and fairly large concentrations have only been found in the vicinity of the Ekofisk
and Forties oil-producing platforms (Oppenheimer et a1. 1977). Naturally, it takes
time after an oil spill until an optimal number of oil-decomposing bacteria is
present.
The efficiency of these bacteria depends on a number of environmental factors.
According to some experiments, at low temperature biodegradation is very slow. At
freezing point temperature, they only degrade around 10% of the amount they
would at 25°C. However, there are other experiments which indicate that sometimes
degradation at low temperatures is not much less than at warm temperatures. As a
rule petroleum alone does not contain enough nutrients like nitrogen and phosphorus
74