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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the dispersed oil and the non-dispersed oil may affect different sensitive areas and therefore
may require prioritisation of resources to be preserved.
Habitats/resources should be considered as a whole and not independently, as the decision of
applying dispersant may benefit to particular habitat/resource and at the same time affect
adjacent ecosystems. For example, if an oil spill occurs in shallow water above submerged
coral reef with current and wind conditions leading the slick toward mangrove swamp, it is
advisable to disperse the oil above the reef (even though it may increase oil exposure of the
corals) in order to avoid oil from becoming incorporated into the mangrove sediments from
where it will seep out over the years thereby forming a chronic pollution source for both the
mangrove and coral reef ecosystems.
Figure 14: Field experiment conducted on mangrove with dispersed oil in order to
assess the impact of the dispersion in TROPIC experiment (source: Clean Caribbean)
The NEBA process takes time and should be planned in advance. In order to conduct a NEBA
it is essential to list resources present in an area by order of the protection priority. Such list
should take into account factors such as possible seasonal variations which may affect
priorities. When drawing up such a list, both natural and economic resources should be
considered. In general it can be said that endangered species, highly productive areas,
sheltered habitats with poor flushing rates, habitats which take a long time to recover should
receive top protection priority.
In Part III of these Guidelines, the reader will find elements of practical guidance for conducting
a NEBA process.
9.
TESTING, ASSESSMENT AND SELECTION OF DISPERSANTS
Indiscriminate use of dispersants in combating oil spills may have deleterious effects on the
marine environment and therefore most of the countries, which consider the use of dispersants
as part of their oil spill response strategy, have developed certain criteria or specifications with
which dispersants should comply.
These specifications may be used for the selection of the most adequate products on an
informal basis, while some countries have established formal approval criteria.
For the moment, there are no real agreements at international level on these criteria, despite
the efforts made by intergovernmental bodies such as European Maritime Safety Agency
(EMSA) or Bonn Agreement while trying to harmonise the use of dispersant in their respective
region. However, on a case by case basis, instead of setting their own approval procedure,
some countries would simply follow other countries approvals for dispersants. For instance,
Croatia accepts certain products approved in other countries such as Cyprus, France, and
United Kingdom. Another example is Israel, which accepts products approved by CEDRE.
Most often the specifications are based only on the effectiveness and toxicity testing of
products. In addition, some countries have set standards on the biodegradability of the product
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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and/or dispersed oil. There are also countries which specify required physical characteristics of
dispersants which may be used.
On the basis of screening tests for any of these characteristics, individual competent national
authorities develop their lists of approved products, which might be used in conformity with the
approved response strategy.
There is also no agreement on testing procedures between different national administrations.
However, regardless of the tests chosen, these should allow for ranking of products with regard
to their relative effectiveness, toxicity or biodegradability.
All known testing procedures are based on laboratory tests. Such tests are not aimed at
simulating real field situations and are accordingly designed to give relative values of tested
properties. Field experience shows that there are no significant discrepancies between relative
values obtained in laboratory tests and behaviour of tested products in the field, although
differences sometimes appear. The same applies to the comparison between results of
different tests: although absolute values can largely differ for a specific characteristic of a
tested dispersant, depending on the testing procedure used, products which show better
results according to a certain procedure, normally also appear superior when tested in
accordance with another procedure.
The main concern in the early years of the use of dispersants was their toxicity. With the
development of new, much less toxic formulations, more and more attention has been paid to
the efficiency of dispersants. At present, the effectiveness of dispersants is the most
important selection criteria. It is considered that toxicity, as well as biodegradability, of an
ineffective product are irrelevant. The objective is to select a product with the best possible
combination of relatively high effectiveness and relatively low toxicity.
Regardless of specific test procedures, a generally accepted testing pattern follows several
common steps. The effectiveness of the product is tested first. Products which pass this
criterion are then tested on toxicity and biodegradability. Results of toxicity and biodegradability
tests are compared, and the products which pass defined criteria are approved for possible
use.
9.1
Effectiveness tests
Most of these tests measure the degree and/or the stability of dispersion (droplet size
distribution) either by visual observation or by some kind of analytical technique, after mixing oil
and dispersants under standard conditions.
The measurement of the lowering of interfacial tension between oil and water following the
addition of a dispersant or the speed of resurfacing of dispersed oil after mixing can also be
used for the assessment of the dispersant's efficiency.
The differences in results and rankings often originate from differences in the parameters of the
tests (type of oil, temperature, oil and water volumes, dose rates, contact between the
dispersant and the oil
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application or premixed level and type of mixing energy, close test tank
of continuous dilution, test duration, etc. Refer to table in the next page).