50 
Wahrendorf - Meta-analysis on experiences from Deep-Water Horizon 
A first evaluation of the main topics was also carried out by the members of the German In 
dependent Environmental Group of Experts “Consequences of Pollution Incidents“ (UEG) in 
a report in 2011 (UEG 2011). Several aspects and interactions of the afore-mentioned topics 
are currently still discussed in the scientific communities. Because of the complexity and the 
huge amount of information, in this context only some findings with relevance for an imple 
mentation in the oil spill response and contingency planning are presented for selected top 
ics. 
Process understanding, distribution, fate and degradation 
Due to the high temperatures in the Gulf of Mexico, high amounts of volatile oil components 
evaporated into the atmosphere. The degradation of the remaining oil components occurs 
under aerobic as well as anaerobic conditions, whereas the aerobic degradation is generally 
quicker. NOAA (National Oceanic and Atmospheric Administration) estimates that approxi 
mately 64.000 t of oil per year reach the Gulf of Mexico by natural processes like oil seeps. 
Therefore it is assumed the oil degradation processes in the gulf had a shorter lag phase. 
Microbiological degradation processes are only known roughly, likewise the impact of the 
applied dispersants is unknown. It was measured, that the decomposition of methane at first 
was very fast and then was reduced dramatically at the end of June, the reasons are yet un 
known. 
Figure 8.5: Interaction of A. borkumensis with different dispersant surfactants at the oil-water interface 
(from Bookstaver et al. 2015). 
There is no clear conclusion on the efficiency of the application of dispersants and its influ 
ence on the microbiological communities and processes. Currently it is highly debated if dis 
persants promote or suppress the biodegradation of oil compounds. Bookstaver et al. (2015) 
propose that the degradation possibly depends on the dispersant product and its surfactants 
that are applied. They analysed the hydrocarbon degrading bacterium Alcanivorax borku 
mensis and its growth at the interface of oil and water. Low levels of negatively charged (ani 
onic) surfactants repelled A. borkumensis, whereas low levels of the neutrally charged 
(nonionic) surfactant nearly doubled its growth rate compared to a control, see Figure 8.5. Of 
the surfactants tested only Tween 20 assists the bacterial growth, Corexit EC9500A affected 
the growth negatively. Apparently not every surfactant does enhance the natural degradation 
abilities of bacteria, since the applied anionic surfactants repel the bacteria with its own bio 
surfactants (Bookstaver et al 2015). The use of non-ionic surfactants (as Tween 20) should 
be investigated further. 
Corexit EC9500A was applied in the Gulf of Mexico. In contrast to North-Amerika Corexit is 
not stored in relevant amounts in the European stockpiles (EMSA 2014). The dispersants in 
the European stockpiles with higher capacities are: Dasic Slickgone NS, Gamlen OD4000, 
Inipol IP80, Finasol OSR62, Dispolene 36S, BP Enersperes 1583, Finasol OSR65, Dasic 
Slickgone LTSW.