TIIE PROBLEM OH’ OIL POLLUTION OF THE SEA
27 1
B. Dispersal, sinking and recovery at sea
It is always preferable to deal with spilt oil on the water, before it
reaches the shore. I n reasonable weather conditions it is usually easy
to transport and apply dispersing or sinking agents by ship. When
these are toxic, their rapid dilution and the relative scarcity of plants
and animals in the open sea makes for far less biological damage than
their application directly onto the densely-populated intertidal zone.
I n treating oil spillages in European waters, the method most used
so far has been to spray with solvent-emulsifiers. The more effective
of these, such as B P 1002, Gamlen, Fina-Unisol or Essolvene, contain
8-30% non-ionic surfactant and 60-80% hydrocarbon solvent (usually
of high aromatic content) with additional emulsifiers and stabilizers
(some formulations are given by Smith, 1968). They are designed to
be laid on the oil in a fine but powerful spray without dilution. Under
laboratory conditions as little as 10% of the oil volume produces a
stable milky emulsion after shaking, although in the field any quantity
from 25% to twice the oil volume may be needed. The mixture must
tht JI be agitated vigorously to disperse it as an oil-in-water emulsion.
This can be accomplished by making a faster return journey through
the slick (or using a following vessel) to break it up by propeller action,
or with high-pressure water hoses. Some surfactant mixtures are effective without the addition of hydrocarbon solvents and can be applied
in polar liquids (water or alcohols). Examples of these are the American
Corexit (see Moore, 1968) and Polycomplex-A (Spooner, 196th) or the
British Dispersol 0s. Crop-spraying aircraft might appear to be suitable for applying dispersants, but the payload is very small if they have
to fly over any distance (Wardley Smith, 1968b). A Canadian aircraft
used for fighting forest fires carries a payload of ten tons of water and
could be modified to deliver dispersants. The mixture could not be
agitated from fixed-wing aircraft, although Moore suggested that the
rotor-wash from a helicopter might be adequate.
Oil can be sunk by the addition of any fine, dense material-for
example, dry sand-as often happens naturally ; unfortunately, it
then coagulates on the bottom into large globules which rise at the
slightest disturbance. Because of this, and due to fears that sunken
oil might smother shellfish beds, interfere with fish feeding or breeding
grounds and foul nets or pots, British official policy seemed until very
recently to be opposed to sinking oil. I n America, Carbosand (sand
coated with heavy oil and then heated sufficiently to char the coatingsee Hofmann, 1949) has been in use for some years, but it is not an
effective oil-binder (Schneider and Beduhn, 1967) and is rather toxic
27 1
B. Dispersal, sinking and recovery at sea
It is always preferable to deal with spilt oil on the water, before it
reaches the shore. I n reasonable weather conditions it is usually easy
to transport and apply dispersing or sinking agents by ship. When
these are toxic, their rapid dilution and the relative scarcity of plants
and animals in the open sea makes for far less biological damage than
their application directly onto the densely-populated intertidal zone.
I n treating oil spillages in European waters, the method most used
so far has been to spray with solvent-emulsifiers. The more effective
of these, such as B P 1002, Gamlen, Fina-Unisol or Essolvene, contain
8-30% non-ionic surfactant and 60-80% hydrocarbon solvent (usually
of high aromatic content) with additional emulsifiers and stabilizers
(some formulations are given by Smith, 1968). They are designed to
be laid on the oil in a fine but powerful spray without dilution. Under
laboratory conditions as little as 10% of the oil volume produces a
stable milky emulsion after shaking, although in the field any quantity
from 25% to twice the oil volume may be needed. The mixture must
tht JI be agitated vigorously to disperse it as an oil-in-water emulsion.
This can be accomplished by making a faster return journey through
the slick (or using a following vessel) to break it up by propeller action,
or with high-pressure water hoses. Some surfactant mixtures are effective without the addition of hydrocarbon solvents and can be applied
in polar liquids (water or alcohols). Examples of these are the American
Corexit (see Moore, 1968) and Polycomplex-A (Spooner, 196th) or the
British Dispersol 0s. Crop-spraying aircraft might appear to be suitable for applying dispersants, but the payload is very small if they have
to fly over any distance (Wardley Smith, 1968b). A Canadian aircraft
used for fighting forest fires carries a payload of ten tons of water and
could be modified to deliver dispersants. The mixture could not be
agitated from fixed-wing aircraft, although Moore suggested that the
rotor-wash from a helicopter might be adequate.
Oil can be sunk by the addition of any fine, dense material-for
example, dry sand-as often happens naturally ; unfortunately, it
then coagulates on the bottom into large globules which rise at the
slightest disturbance. Because of this, and due to fears that sunken
oil might smother shellfish beds, interfere with fish feeding or breeding
grounds and foul nets or pots, British official policy seemed until very
recently to be opposed to sinking oil. I n America, Carbosand (sand
coated with heavy oil and then heated sufficiently to char the coatingsee Hofmann, 1949) has been in use for some years, but it is not an
effective oil-binder (Schneider and Beduhn, 1967) and is rather toxic