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On 18 March 1967, RAF Buccaneer bombers dropped napalm on the Torrey
Canyon, an oil tanker which had run aground 25 kilometres west of Lands
End. The planners thought that setting fire to the ship would burn off the
oil pouring into the sea. Instead the slick contaminated 220 kilometres
of beaches, giving Britain its first taste of cleaning up oil spills. The
black slime slid up estuaries and into harbours, and the 10 000 tonnes of
detergent applied to the mess turned out to be so toxic that it decimated
the intertidal life that had survived the oil, such as crustaceans. Chemicals
for cleaning up spills have never recovered their reputation in this country.
Yet for commercial, practical and political reasons, those chemical dispersants
are still preferred to mechanical booms and skimmers.

After the Braer ran aground at Garth’s Ness off Shetland in horrendous
weather earlier this month, some local politicians, and even scientists,
suggested that it should receive the same indelicate treatment as the Torrey
Canyon. The implication was that once the oil had burned and the smoke had
cleared, the local residents would be spared months of protracted, messy
cleaning and could resume their normal lives.

EXPERIMENTS IN OILS

Has there been no progress in 25 years? While oil spill science has
come a long way in the laboratory and in computer simulations, it still
has to prove itself consistently in practice. Every spill is an entirely
new experiment, subject not only to the weather but also political and economic
factors. The 35 000 tonnes spewed by the Exxon Valdez into Alaska’s Prince
William Sound in March 1989 may have ranked only 23rd in the world’s ‘super
spill’ league, but the subsequent publicity, lawsuits, and testing of new
techniques designed to enhance natural bacterial breakdown of the oil caught
the attention of the world.

Some countries have invested considerably in the hope of being better
prepared than Alaska was, where the cleanup cost $2 billion. In June 1989
the Norwegian government permitted a team of American and Norwegian scientists
to carry out an experiment in which the tanker Esso Bergen deliberately
spilt over 40 cubic metres of crude oil 110 kilometres off the northwest
coast of Norway as part of a five-day study costing $600 000. They tracked
the path of the slick with electronic buoys which measured physical and
chemical changes in the water; the slick drifted 65 kilometres in four days
and broke up. En route, 500 samples were collected to test the effectiveness
of various chemical dispersants. Yet the data proved of little use when
later that same summer, in rather worse weather, the Brazilian bulk carrier
Mercantil Marica spilt hundreds of tonnes of fuel oil – which is heavier
than crude – into the inshore waters of Sognefjord, a long fjord north of
the port of Bergen. Mechanical booms failed to stop the slick reaching many
shores up and down the fjord.

Mechanical booms are the most effective means of containing and removing
spilled oil. They rely on the fact that oil floats on water: in a slick
it initially forms a layer a few millimetres thick. Floating booms consisting
of inflatable ballasted tubes made of neoprene polymer can block oil up
to a metre above and below the surface, but they cannot be used in weather
worse than Force 4 gales – equivalent to wind gusting at 35 kilometres per
hour. (The Braer went aground in Force 9 gales.) Once these corral the oil,
stainless steel skimmers can be lowered into the oil, which is then sucked
in and pumped to containers. However, in currents of more than 1.5 knots
the oil can creep underneath the booms, and splash it over the top in winds
of more than 50 kilometres per hour. Few ships have accidents in such relatively
calm conditions. Booms are also expensive, costing from £50 to
£200 per metre. Also, they only recover a maximum of 10 per cent of
the spilt oil.

Some boom suppliers think that in Britain the oil companies have not
provided enough funds to develop new ideas that would make mechanical recovery
more viable in typical British sea conditions. New designs exist for exposed
locations, but would need up to £250 000 of funding over several
years to get them into field trials. If the oil companies would put up some
of that, the suppliers and government have indicated that they would provide
the rest.

However, many oil companies actually make dispersants, which are used
in factories and storage sites, as well as at sea. Allowing for the cost
of hiring boats and planes, both technologies cost about the same (roughly
£3000 to treat 100 tonnes of oil). But dispersants have a cosmetic
effect too: they take the oil out of sight.

Like Norway, Britain has thousands of kilometres of craggy, often inaccessible,
coastline and severe weather in winter. The combination has persuaded the
Department of Transport’s Marine Pollution Control Unit to gear up for rapid
spraying of dispersants, rather than boom deployment, to prevent oil from
reaching beaches. The first line of attack is a Cessna spotter plane fitted
with radar and ultraviolet and infrared imaging equipment to detect, track
and assess the quantity and direction of a slick, and eight ageing Dakota
aircraft, each able to carry 6800 litres of dispersant and ready for takeoff
at 30 minutes’ notice.

Dispersants reduce the surface tension that usually makes oil and water
immiscible. The oil turns into tiny droplets, and a solvent in the dispersant
spreads those down into the water column, so booms are less effective with
dispersants. Natural processes such as oxidation and biodegradation eventually
turn the droplets into water, carbon dioxide, oxygen, inorganic salts and
inert materials. However, for maximum effectiveness dispersants must be
added as soon as possible, usually within 48 hours, because the denser components
which are left behind form a mousse (a foamy, stable mixture of air, water
and oil) which makes it harder for the dispersant to act.

The toxicity and effectiveness of dispersants are being studied at Warren
Spring Laboratory in Stevenage, and an approved list drawn up by the Ministry
of Agriculture, Fisheries and Food. The dispersants used in Shetland were
specially developed as concentrates for aerial spraying, and are claimed
to be more effective on oils that have been in the water for some time.

However, doubts about the safety of dispersants persist. If oil is allowed
to remain on the surface then its toxicity decreases as the more volatile
components evaporate. Forcing those components down into the water column
means they can contaminate organisms, such as fish eggs and larvae, kelps,
and communities on the seabed like sea urchins and lobsters, that may have
escaped harm from surface oil. Birds and mammals that have escaped surface
oiling will eat the contaminated food, and the natural oils that lubricate
their fur and feathers may also be affected.

In the search for the best dispersant for each situation, a team led
by Per Daling, senior scientist in the Environmental Department at Norway’s
Institute for Continental Shelf and Petroleum Technology Research (IKU)
in Trondheim, has since 1988 studied the behaviour and weathering properties
of various North Sea crudes in slick form.

Samples of different crudes produced and transported in Norwegian waters
are first prepared in the laboratory to make them similar to oils exposed
to weathering processes such as evaporation and emulsification. Data from
mass spectrometry, gas chromatography and other processes are then processed
in a numerical simulation model, which predicts the drifting and likely
life of a slick under various weather conditions. The IKU team has also
looked at the effectiveness of various dispersants on weathered crudes,
and produced a series of handbooks for oil companies detailing the likely
effectiveness of various chemicals on different crudes, as well as the deadlines
for optimal use of mechanical and chemical measures to combat slicks.

The oil spilled off Shetland came from the Gullfaks field, northwest
of Bergen, which by chance was one of the first that Daling’s team studied.
He describes Gullfaks crude as being ‘rather special’, having a low wax
and asphaltene content. Its low content of volatile components reduces evaporation
compared to other crudes, and it is slow to emulsify and form a mousse.
Theoretically, that should make it one of the easiest to clean up mechanically
from a beach.

MOPPING-UP PROCEDURES

The physical cleanup at Prince William Sound took months, during which
the 1600 kilometres of shoreline were attacked with an array of barges,
booms, skimmers, pumps, and even shredded plastic mops, though very little
dispersant. The beaches were also hosed with hot water to flush oil into
the sea. This sparked yet more controversy: some workers claimed that this
would further damage shoreline organisms by effectively killing them and
sterilising their environment; Exxon scientists, on the other hand, insisted
the technique – seldom used before in such cold weather – stimulated local
microbiological activity.

Natural biodegradation was helped along in a field test in Alaska that
formed part of the final shoreline cleanup; the encouraging results suggest
it may be tried in the coming months on selected sites in Shetland. The
world’s oceans are rich in bacteria capable of breaking down naturally occurring
hydrocarbons such as dead organisms. But their growth is largely determined
by the availability of the oxygen and nutrients they need – particularly
nitrogen and phosphorus. During an oil spill, the natural populations will
only be limited by existing nutrient supplies. ‘Bioremediation’ techniques
aim to augment the growth of these oil-degrading communities.

In Alaska, the shoreline that had been hosed with hot water was seeded
with slow-release fertiliser containing nitrogen, phosphorous and urea.
Within a few weeks comparison with a control area showed that breakdown
of residual oil by the resident microbes had speeded up. The fertiliser
used was granular and water-soluble, and scientists at manufacturer Elf
Aquitaine claim that adding oleic acid, a fatty acid, catalyses the degradation
process in sandy sedi-ments, which are more difficult to clean than pebbles
because the oil permeates further, the particles have a larger total surface
area, and there is less ambient oxygen.

Shaunagh Kirby is a freelance journalist.