Prestige: Fate of the oil at sea
The viscosity of the crude increased steadily as the Prestige’s
crude oil divided slowly but gradually into patches and smaller
slicks which became increasingly difficult to see from the air and
keep track of for the spotter planes as the tar balls broke down
into even smaller tar balls that either floated on the water surface
or tended to drift around in the upper layers of the water column
throughout the entire Bay of Biscay.
One of the reasons why this
spill was so unique was the fact that as the slick steadily broke
up into bigger or small patches and as 15000 to 20000 tonnes of
oil were spilled and never recovered, there is a real potential
threat for oil to keep coming ashore for quite some time to come
and that is difficult to evaluate.
The
main physical and chemical properties of the crude from the Prestige
were swiftly analysed by Cedre so as to pinpoint the chemical composition
of the crude and measure the aromatic fraction content in addition
to density and viscosity. Crude oil finger printing techniques were
used to identify the oil that was collected at sea.
All in all,
lab technicians conducted 120 operational-administrative analyses
in addition to 160 judicial analyses upon request from the Office
of the Public Prosecutor in Brest. Cedre posted the requisite information
on its website as to how to conduct the analyses and gave laboratories
benchmark-reference samples whenever requested to do so.
Ifremer
and the French Petroleum Institute conducted a number of analyses
of the collected crude samples but it was IFP that actually computed
the capacity of the soluble fractions of the oil to diffuse throughout
the water column.