BfR-Wissenschaft 
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Dispersant application dosage 
Each dispersant formulation has its own specific dosage requirement which is defined by the 
supplier or manufacturer, i.e. the application conditions and the Dispersant Oil Ratio (DOR). 
Nevertheless, in the event of a spill, it is important to adapt the dosage according to the 
characteristics of the spilled oil and its state of weathering. In practical terms, the DOR has to 
be adapted to the oil quality. In France, the following rules apply: 
• Non-emulsified product 
A ratio of 5%, a Dispersant: Oil Ratio (DOR) = 1:20 
• Emulsified product 
A ratio from 2 to 5%, a Dispersant: Emulsified Oil Ratio = 1:50 
• Highly viscous oil 
Non-emulsified: DOR =1:10 
Emulsified: double spraying, the first to break the emulsion (1:50), the second to dis 
perse the oil (1:20) 
French dispersant approval procedure 
In France, dispersants have to be evaluated prior to any use in the environment according to 
a procedure based on three standardised tests. The aim of this procedure is to choose the 
most efficient and the least toxic dispersants. 
This procedure aims at characterising the dispersant’s efficacy (Efficiency test or IFP test, NF 
T90 345), its ecotoxicity (Toxicity test, NF T 90 349) and its persistence in the environment 
(Biodegradability test, NF T 90 346). The two latter tests are conducted on the pure formula 
tion, i.e. without adding any oil. 
For ecotoxicity testing, France decided to test the pure product, as 3 rd generation dispersants 
are typically less toxic than the spilled oil. Moreover, the toxicity of the spilled oil largely de 
pends on its chemical nature, notably on its content of aromatic components, and their re 
spective bioavailability. The more efficient a dispersant is, the more oil components will be 
present in the water column and the greater its bioavailability. Therefore, the more efficient 
the dispersant, the higher the toxicity of the oil/dispersant mixture. As a consequence, basing 
the toxicity assessment on the dispersant/oil mixture will systematically eliminate the most 
effective products in terms of dispersion. For this reason, France has decided to base its 
assessment on the intrinsic toxicity of the dispersant, i.e. on the pure formulation. 
Conclusion 
The use of dispersant to respond to an oil spill has always been controversial, and discus 
sions on this issue have intensified in recent years in the aftermath of the Deepwater Horizon 
accident. 
However, since the first use of dispersants in an accidental context, enormous advances 
have been achieved not only with regard to their efficacy, but also to their biodegradability. 
Furthermore, the intrinsic toxicity of 3 rd generation dispersants is very low and systematically 
lower than that of dispersed oil. 
Despite these encouraging points, it has to be recalled that further studies are required in 
order to better assess the consequences of subsea injection of dispersants and to under