OIL AND RELATED CHEMICALS - Marine Pollution: What Everyone Needs to Know - page 71

miles long in deep water over 3,000 feet below the surface was
discovered, residue from the well blowout. The continuous
plume of oil persisted for months without substantial biodeg-
radation. Dissolved oxygen concentrations suggest that micro-
bial respiration in the plume was low. The dispersants created
dispersed oil plumes in deep water because the high pressures
and low temperatures made the mixture of oil, dispersants,
seawater, and methane neutrally buoyant. Subsequently, it
was found that much of the dispersant itself was contained in
the plume in the deep ocean and had still not degraded three
months after it was applied; it seemed to have become trapped
in deepwater plumes. The toxicity of this mixture on deep sea
communities is unknown, as are the impacts on planktonic
filter feeders and fish eggs and larvae in the water column.
Eventually microbial activity degraded the oil. If dispersants
had not been used, the surface oil might have been weathered
into tar balls by the time it reached the coast. This would have
created a public relations nightmare on beaches and affected
the socioeconomic activities of residents and tourists. The
dispersed oil below the ocean surface appears to have killed
benthic animals in intertidal and shallow subtidal regions on
and near sandy beaches. In the wetlands only the fringe-edge
marsh plants were damaged by the toxic oil and dispersants,
since these plants appear to have absorbed the chemicals that
caused the death of shoots.
The Deepwater Horizon blowout was unprecedented
because of the use of dispersants at the wellhead, resulting
in subsurface retention of oil as finely dispersed droplets and
emulsions and deepwater retention of plumes of natural gas
that underwent rapid microbial degradation. Eventually nat-
ural oil-degrading bacteria worked on the plumes and rapid
degradation took place, despite the low 5°C temperature. This
took place in the deep water, as a result of the geography of the
Gulf of Mexico, which is fairly enclosed. When the hydrocar-
bons were released from the well, bacteria bloomed and then
swirled around in the currents and often came back repeatedly