BfR-Wissenschaft 
13 
4 What are dispersants? 
Stéphane Le Floch 
Centre of Documentation, Research and Experimentation on Accidental Water Pollution 
(Cedre), Brest, France 
Introduction 
When a spill occurs, whether it be an oil tanker releasing its cargo at sea or a subsea well 
head blowout, the oil released into the environment will constitute a major source of pollution. 
Although the intensity of this contamination will be directly proportional to the quantity spilt, 
this contamination can be considered as a major event which will systematically have disas 
trous consequences for the environment. As soon as oil has been released into the environ 
ment, the response authority is in charge of mitigating the environmental impact, i.e. minimis 
ing both the effects of the oil on marine flora and fauna and choosing the response tech 
niques which will be least harmful for the marine ecosystem. 
The authorities must deal with the following situation: oil is accidentally released in the envi 
ronment, a significant environmental impact is likely, and the response strategy to be de 
ployed must be considered quickly. In addition, this strategy must be defined taking into ac 
count the intrinsic impact of the selected response techniques, for instance the impact of 
heavy equipment on the shoreline during operations to recover stranded slicks. 
The spill response can be divided into two strategies which, according to the situation, may 
be complementary. These strategies consist in: 
1. Removing the oil from the environment, whether at sea through containment and 
pumping operations or on land through manual or mechanical collection, bearing in 
mind that in both cases the oil collected will need to be treated as waste. 
2. Treating oil slicks directly in the environment, whether at sea through chemical 
dispersion or in situ burning operations or on land through bioremediation operations 
on stranded oil or oil trapped in the sediment matrix. 
While response authorities tend to choose option 1 as the main priority, i.e. recovering the 
spilt oil, it may be advisable, in certain clearly identified cases, to choose option 2, i.e. treat 
the oil slick directly in the environment. This article aims to present the chemical dispersion 
technique for oil slicks at sea (option 2) by defining dispersants, describing how they work, 
outlining the environmental constraints affecting their efficiency and providing an introduction 
to the tests applicable in France for their approval. 
General concerns relating to dispersant use 
The use of dispersant is a highly controversial matter. At issue is whether the risk of ecologi 
cal effects on marine species from toxic oil components increases or decreases when oil 
slicks are dispersed before they reach the shoreline (Fucik, 1994). The main objective of 
dispersant use is indeed the transfer of oil from the water surface into the water column. As a 
result, exposure for surface dwelling and intertidal species is potentially decreased, while it is 
increased for pelagic and benthic organisms. Thus, inherent to the use of dispersants is the 
implicit trade-off among different habitats and species with different ecological, social, and 
economical values. This controversy was further amplified following the Deepwater Florizon 
accident (Claireaux G, 2013). 
Consequently, it is important to remember that the primary aim of this response technique is 
to minimise the overall environmental impact of an oil slick drifting at sea by transforming it