On the first day of the "Torrey Canyon" accident, in 1967, attempts were made to
disperse the oil with dispersants. This reaction was understandable in view of the
danger that the tanker's whole load might spread out along the coasts of the English
Channel and possibly penetrate into the North Sea. So that the beaches would be fit
for the approaching summer tourist season, detergents were used in large quantities
to clean up the fouled coasts of Cornwall. In all, 10,000 t of dispersants and detergents were used to combat approximately 14,000 t of weathered oil. Biologically,
more damage was done by the dispersants applied than would have been done by the
oil. The dispersants applied in the "Torrey Canyon" accident were fairly poisonous.
"BP 1002" was mainly used, a product with 12% nonionic detergents and 3% stabilizers in an aromatic solvent. The toxicity of "BP 1002" for subtidal organisms is
0.5-5 mg/l expressed as 24 h LCso , the concentration which kills half of the experimental animals within 24 h. Toxicity for intertidal animals is 5-100 mg/l. In practice
all animal life was killed where beaches had been cleaned with such types of dispersants (A.1. and E.C. Southward 1978).
As the consequence of such experience the Federal Republic of Germany decided
not to use detergents in case of an oil spill, except in a few situations. According to
the Helsinki Convention (see Chap. 10) dispersants are not allowed in the Baltic. In
the U.S.A. they were only allowed to fight oil spills of more than 30 t on water more
than 150 m deep and never close to a shore (Boesch et al. 1974).
In the meantime, however, the question of chemicals for fighting oil spills is again
under discussion. Dispersants have been developed which are only about Ij1000th as
toxic as "BP 1002", for example "BP 1100" and "Corexit 7664", and for some of
them the 48 h LCso is as low as 10 gil. In Great Britain such dispersants are licenced
for sea use which have a 48 h LCso of above 3.3 gil, and the toxicity of an oil-dispersant mixture must not be higher than the toxicity of oil alone (Table 19). In 1975,
on the coasts of Great Britain there were stocks of dispersants available to fight an oil
accident of 35,000 t.
Dispersants are surface-active substances which enhance the formation of small,
1-5 11m diameter droplets of oil suspended in the seawater, so that the oil slick disappears from the surface of the sea. The oil droplets, under the influence of dispersants, do not stick to the surface of particles or of the sediment. At the beginning of
the use of dispersants for fighting oil spills, about 1 t of dispersant was necessary to
disperse 1 t of oil. Modern concentrates can be used 1 :30. Further, it is no longer
necessary to provide good mixing of dispersant, oil, and water; modern dispersants
are rather self-mixing so that some may be applied from airplane or helicopter.
Important is the exact timing: even if it is an open question to what extent dispersed
oil can disappear from the water column by evaporation, it seems reasonable to allow
the light, volatile fractions of the oil to evaporate before dispersal; then the explosion
risk is avoided during operations. On the other hand, spraying should be done before
a water-in-oil emulsion, the "chocolate mousse" is formed, because this is much more
stable and more difficult to disperse than an oil slick. One should keep in mind that
dispersal of oil following an oil accident is done not only by chemicals, but to a fairly
large degree, depending on the weather, by natural processes, too, and that under
favorable conditions small oil spills may be dispersed by the stirring effect of a motor
boat's propeller (Moss 1971).
98
disperse the oil with dispersants. This reaction was understandable in view of the
danger that the tanker's whole load might spread out along the coasts of the English
Channel and possibly penetrate into the North Sea. So that the beaches would be fit
for the approaching summer tourist season, detergents were used in large quantities
to clean up the fouled coasts of Cornwall. In all, 10,000 t of dispersants and detergents were used to combat approximately 14,000 t of weathered oil. Biologically,
more damage was done by the dispersants applied than would have been done by the
oil. The dispersants applied in the "Torrey Canyon" accident were fairly poisonous.
"BP 1002" was mainly used, a product with 12% nonionic detergents and 3% stabilizers in an aromatic solvent. The toxicity of "BP 1002" for subtidal organisms is
0.5-5 mg/l expressed as 24 h LCso , the concentration which kills half of the experimental animals within 24 h. Toxicity for intertidal animals is 5-100 mg/l. In practice
all animal life was killed where beaches had been cleaned with such types of dispersants (A.1. and E.C. Southward 1978).
As the consequence of such experience the Federal Republic of Germany decided
not to use detergents in case of an oil spill, except in a few situations. According to
the Helsinki Convention (see Chap. 10) dispersants are not allowed in the Baltic. In
the U.S.A. they were only allowed to fight oil spills of more than 30 t on water more
than 150 m deep and never close to a shore (Boesch et al. 1974).
In the meantime, however, the question of chemicals for fighting oil spills is again
under discussion. Dispersants have been developed which are only about Ij1000th as
toxic as "BP 1002", for example "BP 1100" and "Corexit 7664", and for some of
them the 48 h LCso is as low as 10 gil. In Great Britain such dispersants are licenced
for sea use which have a 48 h LCso of above 3.3 gil, and the toxicity of an oil-dispersant mixture must not be higher than the toxicity of oil alone (Table 19). In 1975,
on the coasts of Great Britain there were stocks of dispersants available to fight an oil
accident of 35,000 t.
Dispersants are surface-active substances which enhance the formation of small,
1-5 11m diameter droplets of oil suspended in the seawater, so that the oil slick disappears from the surface of the sea. The oil droplets, under the influence of dispersants, do not stick to the surface of particles or of the sediment. At the beginning of
the use of dispersants for fighting oil spills, about 1 t of dispersant was necessary to
disperse 1 t of oil. Modern concentrates can be used 1 :30. Further, it is no longer
necessary to provide good mixing of dispersant, oil, and water; modern dispersants
are rather self-mixing so that some may be applied from airplane or helicopter.
Important is the exact timing: even if it is an open question to what extent dispersed
oil can disappear from the water column by evaporation, it seems reasonable to allow
the light, volatile fractions of the oil to evaporate before dispersal; then the explosion
risk is avoided during operations. On the other hand, spraying should be done before
a water-in-oil emulsion, the "chocolate mousse" is formed, because this is much more
stable and more difficult to disperse than an oil slick. One should keep in mind that
dispersal of oil following an oil accident is done not only by chemicals, but to a fairly
large degree, depending on the weather, by natural processes, too, and that under
favorable conditions small oil spills may be dispersed by the stirring effect of a motor
boat's propeller (Moss 1971).
98