THE PROBLEM O F OIL POLLUTION O F THE SEA
267
species (Stone et al., 1942 ; ZoBell, 1964). There is thus little necessity
to " seed " a coastal spill with cultures of specially selected organisms,
nor is there any case for supposing that marine bacteria will show a
lack of enthusiasm for polluting oil, as available carbon is scarce in the
sea (usually less than 2 mg per litre-see Berridge et al., 1968a, and
subsequent comments by Gunkel). Experiments by Gunkel (1967)
showed that, under suitable conditions, normal marine bacteria decomposed nearly 60% of added fuel-oil in 8 weeks. Light oils are oxidized
more rapidly than heavier ones and paraffinic (aliphatic) hydrocarbons
more rapidly than aromatics, according to Stone and his colleagues.
However, Ludzack and Ettinger (1959) observed that aromatic hydrocarbons disappear from polluted streams more rapidly than aliphatics.
This conflict is considered in a review by ZoBell (1950) as being due
mainly to differences in the environment and the types of microorganisms originally present there.
Gunkel (1968 and in Smith, 1968) sampled oiled beaches in Cornwall after the " Torrey Canyon " disaster and found very high numbers
of oil decomposers, especially in well-aerated situations. The greatest
density (over 400 million organisms per ml of wet sediment) was higher
than any he had recorded in previous oil spills and approached the
maximum which could be obtained with pure cultures on artificial
media in the laboratory. The average numbers of oil decomposers at
his Cornish stations varied from one-half to three times the total numbers of other aerobes. Even where there was no oil, he obtained 50 000
oil decomposers per ml. Earlier, ZoBell (1964) had calculated that
after two days' presence of oil in sea water, the population of bacteria
capable of degrading it might reach 8 million per ml. This population
would oxidize about 1 mg oil per litre per day at 25"C, 0.3 mg at 15OC
and less than 0.1 mg at 5 O C . Nitrogen and phosphorus might be
limiting in the water but would probably be adequate in shore sediments. Oxygen is also potentially limiting, but degradation takes place
only at the surface of the oil. The formation of " mousse "-like emulsions may aid the process by increasing the oil-water interface (see
Berridge et al., 1968b and subsequent discussion, also Gunkel discussing
Ramsdale and Wilkinson, 1968). Smith (1968) reported the occurrence
of grey sulphide layers, unusual in Cornish sands, after the " Torrey
Canyon " spill, taking them to be evidence of considerable decomposition of the oil (as might be expected by scaling ZoBell's figures up to
Gunkel's population counts). Anaerobic degradation was occurring at
a much slower rate; this process also depends on the availability of
nitrates, phosphates or sulphates which here provide a source of oxygen.
For example, complete oxidation of 1 mg of a typical mineral oil
267
species (Stone et al., 1942 ; ZoBell, 1964). There is thus little necessity
to " seed " a coastal spill with cultures of specially selected organisms,
nor is there any case for supposing that marine bacteria will show a
lack of enthusiasm for polluting oil, as available carbon is scarce in the
sea (usually less than 2 mg per litre-see Berridge et al., 1968a, and
subsequent comments by Gunkel). Experiments by Gunkel (1967)
showed that, under suitable conditions, normal marine bacteria decomposed nearly 60% of added fuel-oil in 8 weeks. Light oils are oxidized
more rapidly than heavier ones and paraffinic (aliphatic) hydrocarbons
more rapidly than aromatics, according to Stone and his colleagues.
However, Ludzack and Ettinger (1959) observed that aromatic hydrocarbons disappear from polluted streams more rapidly than aliphatics.
This conflict is considered in a review by ZoBell (1950) as being due
mainly to differences in the environment and the types of microorganisms originally present there.
Gunkel (1968 and in Smith, 1968) sampled oiled beaches in Cornwall after the " Torrey Canyon " disaster and found very high numbers
of oil decomposers, especially in well-aerated situations. The greatest
density (over 400 million organisms per ml of wet sediment) was higher
than any he had recorded in previous oil spills and approached the
maximum which could be obtained with pure cultures on artificial
media in the laboratory. The average numbers of oil decomposers at
his Cornish stations varied from one-half to three times the total numbers of other aerobes. Even where there was no oil, he obtained 50 000
oil decomposers per ml. Earlier, ZoBell (1964) had calculated that
after two days' presence of oil in sea water, the population of bacteria
capable of degrading it might reach 8 million per ml. This population
would oxidize about 1 mg oil per litre per day at 25"C, 0.3 mg at 15OC
and less than 0.1 mg at 5 O C . Nitrogen and phosphorus might be
limiting in the water but would probably be adequate in shore sediments. Oxygen is also potentially limiting, but degradation takes place
only at the surface of the oil. The formation of " mousse "-like emulsions may aid the process by increasing the oil-water interface (see
Berridge et al., 1968b and subsequent discussion, also Gunkel discussing
Ramsdale and Wilkinson, 1968). Smith (1968) reported the occurrence
of grey sulphide layers, unusual in Cornish sands, after the " Torrey
Canyon " spill, taking them to be evidence of considerable decomposition of the oil (as might be expected by scaling ZoBell's figures up to
Gunkel's population counts). Anaerobic degradation was occurring at
a much slower rate; this process also depends on the availability of
nitrates, phosphates or sulphates which here provide a source of oxygen.
For example, complete oxidation of 1 mg of a typical mineral oil