THE PROBLEM O F OIL POLLUTION OF THE SEA
237
of emulsions. Some 20 000 tons of crude oil were lost from the “ Anne
Mildred B r ~ v i g ” but never appeared on the nearby beaches of NW
Germany, it is thought because they sank at sea (Stehr, 1967). The
reverse process has been recorded on at least one occasion when about
6 400 tons of heavy fuel-oil were spilt in icy seas, sinking to the bottom
but reappearing later under warmer conditions (Dennis, 1959).
Crude oil emulsifies very readily at sea, forming stable water-in-oil
emulsions which can contain up to 80% water (Berridge et al., 1968b).
Such emulsions are stiff, yellowish-brown in colour and, since the
“ Torrey Canyon ” incident, have become widely known as “ chocolate
mousse ”. The process of emulsification slows down the tendency of a
slick to spread. The viscosity of “ mousse ” is in excess of 1 000 cSt
(Canevari, discussion following paper by Moore, 1968) and it is more
likely to break into ragged patches or “naps ”. However, by the incorporation of so much water, the total amount of material which might
eventually require removal from a beach is considerably increased.
Where there are large quantities of suspended matter, for example
in tidal estuaries, this also becomes incorporated into the oil, increasing
its tendency to break up and sink (Poirier and Thiel, 1941). Chipman
and Galtsoff (1949), observing this, carried out a n investigation on the
intentional removal of oil by sinking with specially-treated sand.
Hartung and Klingler (1968) report several observations on the occurrence of sunken oil in aquatic sediments. Their experiments agree with
those of Chipman and Galtsoff, that increasing salinity reduces the ease
with which oil is sedimented-sinking was most effective in fresh water.
Masses of sunken oil, rolled along the bottom by waves and currents,
accumulatz larger particles of sand, shells and small stones ; appearing
on the beach as hard tarry balls, they are described as ( ( coquina ”
(Dennis, 1959; see also Stander and Venter, 1968). The formation of
these discrete masses of oil probably assists in processes of biological
degradation, which takes place largely at the oil-water interface (see,
for example, Orton, 1925; comments by Gunkel following paper by
Ramsdale and Wilkinson, 1968 ; Langston, 1969).
I n experiments on the rate of spread of small samples of crude oil
on calm waters, Berridge et al. (1968a) found that 9 gal ( 2 $ litres) produced a slick of 7 ft (220 cm) radius in 30-60 s, but in winds exceeding
3 mile/h (1.35 ms - l ) the slicks moved bodily faster than their rate of
spread. Over the long term, the pattern of oil pollution along some
coastlines corresponds predictably with seasonal changes in the strength
and direction of ocean currents (Dennis, 1961). Observations on the
movement of individual slicks at sea suggest that the wind has more
effect than water movements although, in making predictions, due
237
of emulsions. Some 20 000 tons of crude oil were lost from the “ Anne
Mildred B r ~ v i g ” but never appeared on the nearby beaches of NW
Germany, it is thought because they sank at sea (Stehr, 1967). The
reverse process has been recorded on at least one occasion when about
6 400 tons of heavy fuel-oil were spilt in icy seas, sinking to the bottom
but reappearing later under warmer conditions (Dennis, 1959).
Crude oil emulsifies very readily at sea, forming stable water-in-oil
emulsions which can contain up to 80% water (Berridge et al., 1968b).
Such emulsions are stiff, yellowish-brown in colour and, since the
“ Torrey Canyon ” incident, have become widely known as “ chocolate
mousse ”. The process of emulsification slows down the tendency of a
slick to spread. The viscosity of “ mousse ” is in excess of 1 000 cSt
(Canevari, discussion following paper by Moore, 1968) and it is more
likely to break into ragged patches or “naps ”. However, by the incorporation of so much water, the total amount of material which might
eventually require removal from a beach is considerably increased.
Where there are large quantities of suspended matter, for example
in tidal estuaries, this also becomes incorporated into the oil, increasing
its tendency to break up and sink (Poirier and Thiel, 1941). Chipman
and Galtsoff (1949), observing this, carried out a n investigation on the
intentional removal of oil by sinking with specially-treated sand.
Hartung and Klingler (1968) report several observations on the occurrence of sunken oil in aquatic sediments. Their experiments agree with
those of Chipman and Galtsoff, that increasing salinity reduces the ease
with which oil is sedimented-sinking was most effective in fresh water.
Masses of sunken oil, rolled along the bottom by waves and currents,
accumulatz larger particles of sand, shells and small stones ; appearing
on the beach as hard tarry balls, they are described as ( ( coquina ”
(Dennis, 1959; see also Stander and Venter, 1968). The formation of
these discrete masses of oil probably assists in processes of biological
degradation, which takes place largely at the oil-water interface (see,
for example, Orton, 1925; comments by Gunkel following paper by
Ramsdale and Wilkinson, 1968 ; Langston, 1969).
I n experiments on the rate of spread of small samples of crude oil
on calm waters, Berridge et al. (1968a) found that 9 gal ( 2 $ litres) produced a slick of 7 ft (220 cm) radius in 30-60 s, but in winds exceeding
3 mile/h (1.35 ms - l ) the slicks moved bodily faster than their rate of
spread. Over the long term, the pattern of oil pollution along some
coastlines corresponds predictably with seasonal changes in the strength
and direction of ocean currents (Dennis, 1961). Observations on the
movement of individual slicks at sea suggest that the wind has more
effect than water movements although, in making predictions, due