Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
Part II: Basic information on dispersants and their application
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Page 1
P A R T II
BASIC INFORMATION ON DISPERSANTS AND THEIR APPLICATION
1.
INTRODUCTION
Since their first application on a large scale (in the aftermath of the "Torrey Canyon" oil spill
in 1967), the use of dispersants as a response method for combating accidental oil spills has
remained a controversial issue. Although often recognized by clean-up specialists as one of
the most effective methods for dealing with oil spills, chemical dispersion of spilled oil has
numerous setback. The controversy partly stems from lack of information, prejudice and
misunderstanding of the action of dispersants. The opposition to using dispersants is often
also inspired by the results of their insufficiently planned or improper application. The use of
dispersants, especially the decision making process as well as the application process, need
to be planned carefully at national level and supported by an appropriate rational stated in a
policy.
A relatively small number of countries in the Mediterranean region have a clearly defined
policy regarding the use of dispersants. The current status on the policy of use of dispersant
in Mediterranean Coastal States can be consulted on REMPEC‟s Country Profile
(http://www.rempec.org/country.asp
) available on REMPEC‟s website (
www.rempec.org).
The lack of a clear policy regarding dispersants and their use inevitably results in heated
discussions at the time of the spill.
The objective of this document is to provide relevant, up to date information on dispersants
and their place in oil spill response strategy, which may help the Mediterranean coastal
States in creating their policy regarding the use of these products in combating accidental oil
pollution. In this respect the document proposes, in Part III, a standard policy for the use of
dispersants to be used as a model and adapted by States which would set their National
Policy on the Use of Dispersant.
Generally speaking a policy for the use of dispersants should be based on a full
understanding of the action of dispersants and currently utilized application methods and
operational practices, as well as on adopting compatible and, if possible, standardized
procedures for testing and assessing efficiency, toxicity and biodegradability of dispersants
and oil/dispersants mixtures.
2.
THE MEDITERRANEAN SEA: BASIC CONSIDERATIONS
Despite the fact that the Mediterranean sea is an almost closed sea, with limited exchange
of water with the open Atlantic ocean. Generally speaking the volume of the surface sea
water concerned by the dispersion process remains quasi infinite regarding the size of a
possible major oil spill, and would allow a full dilution of a dispersed oil plume and a return to
the background level in such a case.
However, close to the shore and/or in shallow waters the dilution process can meet locally
some limitations which should be taken into consideration in the decision to use dispersants.
Considering the use of dispersants, the Mediterranean surface water is salty water (between
37 and 39.50 g/L from the West to the East) except in the very North of the Aegean Sea due
to the Black sea water supply (18g/L) and close to some large river estuaries or delta.
Guidelines for the use of dispersants for combating oil pollution at sea in the Mediterranean region
Part II: Basic information on dispersants and their application
–
Page 2
The surface water temperature is generally comprised between 18 and 24 °C. Close to the
coast the surface water temperature can exceed 24 °C while during winter in northern parts
it can drop (e.g. Adriatic Sea, 14 °C…)
1
.
Table 1 : Basic considerations for the Mediterranean sea
Surface area (total)
2000 - 3000 m depth contour
less than 200 m depth contour
2.5 x 10
6
km
2
30%
20%
Volume- less than 200 m depth contour
55.5 10
3
km
3
Salinity of surface water
36 to 39.5
Temperature of surface seawater (average)
18 to 24 °C
Tides in the Mediterranean are generally regarded as weak, i.e. tidal amplitudes are much
lower than in the oceans.
Figure 1: Map of the Mediterranean Sea
3.
GENERAL
NOTIONS ON DISPERSANTS
3.1 Definition
Oil spill dispersants are mixtures of surface active agents in one or more organic solvents,
specifically formulated to enhance the dispersion of oil into the sea-water column by
reducing the interfacial tension between oil and water. Natural or induced movement of
water causes a rapid distribution within the water mass of very fine oil droplets formed by the
1
1969-P
r
P Tchernia-
Cours d‟Océanographie Régionale
- Service Hydrographique et Océanographique de la
Marine.