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 22
Table 7: Effectiveness tests parameters
Test ID
Energy
source
Energy
level
Water
volume
Oil/water
ratio
Dispersant
application
method
Dispersant/oil
ratio
Settling
time
IFP
Oscillating
hoop
1-2
4-5
1:1000
Dropwise
variable
1
Labofina
rotating
flask
Rotating
vessel
3
0.25
1:50
Dropwise
1:25
1
Swirling
flask
Shaker
table
1-2
0.12
1:1200
Premix/dropwise 1:10 to 1:25
10
Among the main effectiveness laboratory test procedures:
The LABOFINA test (or WSL test) procedure used in UK which is ran in a separating
funnel in rotation to provide strong energy to promote the dispersion process (ref to
WSL Report LR448. appendix A).
The IFP test (flow through test) procedure used in France which is ran in a test tank in
which the water is renewed in order to reproduce the dilution which would occur at sea;
in this test the mixing energy brought by a wave generator remains gentle (ref: French
standard AFNOR NFT 90-345).
The Swirling test, used in North America, carried out on oil samples premixed which
dispersant in a very small funnel which rotate gently to promote the dispersion process
(ref . ASTM F2059 - 06 Standard Test Method).
The MNS is a very high energy test used in Norway .
Figure 15: the Labofina / WSL test apparatus
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 23
Figure 16: The IFP / flow through test apparatus (source SINTEF)
Figure 17: The swirling flask test method (source:
www.marinemanagement.org.uk/protecting/pollution/documents/approval_lr448.pdf
)
Figure 18: The MNS test apparatus
At last, when a vessel is on site, it is possible to assess the oil dispersibility by collecting a
sample in a glass jar directly from the slick and by testing it in the field. The field test
procedure consist in comparing the dispersion of a sample containing dispersant and oil and
one containing only oil following manual agitation (hand checking). (e.g.
National Plan Oil
Spill Dispersant Effectiveness Field Test Kit - Nat-DET
). Such tests can be useful to oil spill
responders to decide on the opportunity of applying dispersant on oil which degree of
weathering is unknown.
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 24
9.2
Toxicity tests
Test materials are usually dispersants, dispersed oil (oil/dispersant mixture) and sometimes oil
alone. Test species could be fish, arthropods (usually decapod crustaceans), molluscs
(pelecypods), annalids (polychaetes) and algae. Ideally, test species should be selected
among locally significant populations. Tests may be acute (short term) single species, lethal or
sublethal.
The main goals of these tests are to determine the relative toxicity of a certain dispersant
versus other previously tested products.
Due to the increase of toxicity with the increase of temperature, toxicity tests should take into
consideration expected changes in seawater temperature.
Measure of the Lethal Concentration 50 (LC
50
) in a determined period (usually 24 or 48 hours)
is a common criteria used in toxicity tests.
Toxicity testing issue can be considered from two different approaches:
(i)
either, checking the intrinsic toxicity of the dispersant in order to reject the most
toxic ones, in that case only the dispersant is tested;
(ii)
or, checking that the dispersant does not increase the oil toxicity; in that case
the tests are performed on the oil alone and on the oil and dispersant mixture.
Due to the fact that dispersing the oil in the water column lead to increase the oil toxicity of oil
towards the animals living in the water column, the toxicity of the mixture oil and dispersant
should be higher than the one of the oil alone. The more efficient the dispersant, the more toxic
the mixture of oil and dispersant may appear as the oil will be better dispersed. Therefore, such
approach can be more restrictive and eventually reject the most efficient dispersant. This is in
contradiction with the goal of an approval procedure which should be designed to select the
more efficient and less toxic ones.
Considering the objectives of the approval procedure (selection of the best products, i.e. the
less toxic ones), the control of the intrinsic toxicity of the dispersant is sufficient. However the
issue of the toxicity of the dispersed oil remains a concern when considering the policy for the
use of dispersants. The toxicity of the di
spersed oil (toxicity of the “oil and dispersant” mixture)
is required when defining scenarios (environmental conditions) for which the use of dispersant
will remain environmentally acceptable (e.g. part of the NEBA process).
Among the main toxicity tests procedure:
The test procedures in force in United Kingdom :
o
the sea test -comparison on brown shrimp of the toxicity of the oil with and
without dispersant-
o
the rocky shore test
–
effect of the dispersant on the common limpet- ref:
MAFF
Fisheries Research Technical Report Number 102.
The test procedure used in France: comparison of the LC
50
(6h) of the dispersant
alone with the one of a reference toxicant on white shrimp. (ref French standard NF
T90-349).
The standard toxicity test used in United States involves exposing silversides mysid
shrimp to concentrations of the test product and No. 2 fuel oil alone and in a 1:10
mixture of product to oil
(ref:
http://www.epa.gov/osweroe1/docs/oil/cfr/appendix c.pdf
)