branches present, the more difficult is the biodegradation. The smaller the number
of carbon atoms, the more volatile the compounds are, the better they dissolve in
water.
b) Cycloalkanes (naphthenes) with 5-6 carbon atoms arranged in a ring comprise
30%-60% of petroleum. In addition to cyclo-pentane and cyclo-hexane, there are
also bicyclic and polycyclic naphthenes. These compounds are very resistant to
microbial degradation.
c) Aromatic compounds account for 2%-4% of petroleum. Volatile compounds in
ring form (for example, benzene, toluene, and xylene), bicyclic aromatic hydrocarbons (principally naphthalene), tricyclic (like anthracene and phenanthrene), and
polycyclic ones with more than three rings (pyrene, for example) are present (polynuclear aromatic hydrocarbons, PNAH). There are some microorganisms which are
specialized in the biodegradation of these compounds.
Besides hydrocarbons, various other compounds occur in petroleum. Of these, those
containing sulfur are the most important. The sulfur content of petroleum can
amount to up to 10%. Compounds containing sulfur are presumably responsible for
fish and mussels tasting oily after having been in contact with petroleum. In addition,
there are fatty acids (up to 5% oxygen in oil), nitrogen compounds (up to 1 % nitrogen in oil), vanadium, and nickel.
It is known that a number of these compounds are biodegraded by microorganisms.
As for the rest, the biochemical processes of microbiological degradation are complex, and a petroleum component can be approached in different ways by different
taxa (Higgins and Burns 1975).
The different components of crude petroleum are isolated in a refinery above boiling
point. Gasoline has a boiling point of under 200°C and contains compounds with
5-12 carbon atoms. Medium distillates like kerosene, diesel oil, and light heating oil
boil at between 169°-375°C and contain compounds with 9-22 carbon atoms (as
water-soluble, poisonous components, they contain principally naphthalene). Gas oil,
heavy heating oil, lubricating oil and greases boil at higher temperatures and contain
compounds with 29-36 carbon atoms. Residual oils with even higher boiling points
have asphalt-like characteristics.
5.2 Fate of Oil on the Surface of the Ocean
Tanker or (jrilling platform accidents are spectacular. In such cases, great amounts of
crude oil reach the surface of the ocean. Depending on the composition of the crude
oil, their fate is different. The following factors have an effect on the quantity and
the quality of oil on the surface of seawater.
a) Spread: Oil spreads out on the boundary layer between the seawater and the atmosphere. If the quantity is small, an oil film forms that reflects the color spectrum.
100-200 I of oil are sufficient to cover 1 km 2 of sea surface with a film which is
about 0.1 11m thick. Light oils spread faster than heavy oils. Within 10 min, 1 t of
Iranian crude oil spreads to a slick of 48 m diameter and 0.1 mm thickness (Warren
Spring Laboratory 1972). Naturally, the layer on the surface is thicker in massive oil
72
of carbon atoms, the more volatile the compounds are, the better they dissolve in
water.
b) Cycloalkanes (naphthenes) with 5-6 carbon atoms arranged in a ring comprise
30%-60% of petroleum. In addition to cyclo-pentane and cyclo-hexane, there are
also bicyclic and polycyclic naphthenes. These compounds are very resistant to
microbial degradation.
c) Aromatic compounds account for 2%-4% of petroleum. Volatile compounds in
ring form (for example, benzene, toluene, and xylene), bicyclic aromatic hydrocarbons (principally naphthalene), tricyclic (like anthracene and phenanthrene), and
polycyclic ones with more than three rings (pyrene, for example) are present (polynuclear aromatic hydrocarbons, PNAH). There are some microorganisms which are
specialized in the biodegradation of these compounds.
Besides hydrocarbons, various other compounds occur in petroleum. Of these, those
containing sulfur are the most important. The sulfur content of petroleum can
amount to up to 10%. Compounds containing sulfur are presumably responsible for
fish and mussels tasting oily after having been in contact with petroleum. In addition,
there are fatty acids (up to 5% oxygen in oil), nitrogen compounds (up to 1 % nitrogen in oil), vanadium, and nickel.
It is known that a number of these compounds are biodegraded by microorganisms.
As for the rest, the biochemical processes of microbiological degradation are complex, and a petroleum component can be approached in different ways by different
taxa (Higgins and Burns 1975).
The different components of crude petroleum are isolated in a refinery above boiling
point. Gasoline has a boiling point of under 200°C and contains compounds with
5-12 carbon atoms. Medium distillates like kerosene, diesel oil, and light heating oil
boil at between 169°-375°C and contain compounds with 9-22 carbon atoms (as
water-soluble, poisonous components, they contain principally naphthalene). Gas oil,
heavy heating oil, lubricating oil and greases boil at higher temperatures and contain
compounds with 29-36 carbon atoms. Residual oils with even higher boiling points
have asphalt-like characteristics.
5.2 Fate of Oil on the Surface of the Ocean
Tanker or (jrilling platform accidents are spectacular. In such cases, great amounts of
crude oil reach the surface of the ocean. Depending on the composition of the crude
oil, their fate is different. The following factors have an effect on the quantity and
the quality of oil on the surface of seawater.
a) Spread: Oil spreads out on the boundary layer between the seawater and the atmosphere. If the quantity is small, an oil film forms that reflects the color spectrum.
100-200 I of oil are sufficient to cover 1 km 2 of sea surface with a film which is
about 0.1 11m thick. Light oils spread faster than heavy oils. Within 10 min, 1 t of
Iranian crude oil spreads to a slick of 48 m diameter and 0.1 mm thickness (Warren
Spring Laboratory 1972). Naturally, the layer on the surface is thicker in massive oil
72