BfR-Wissenschaft 
33 
Figure 6.3 (reproduced from Schwichtenberg et al. (2016)). White areas in the right panel 
indicate that in no experiment any oil released in these grid cells reached the coast in a one 
week’s time. 
Figure 6.3:10 th percentiles of simulated travel times from a respective grid cell to any sensitive Wadden 
Sea area. Panels refer to untreated (left) and chemically dispersed (right) oil. White areas indicate that no 
oil reached the Wadden Sea within a seven days’ time. The grey (blue) line indicates the 10m (20m) depth 
line. The figure is reproduced from Schwichtenberg et al. (2016). 
Travel time between the location of an accident and sensitive areas is an issue of practical 
importance. In case of untreated oil it defines the time window available for mechanical coun 
ter measures. In case of dispersed oil, large travel times imply the chance for sufficient dilu 
tion (mostly in the vertical) of the oil/dispersant mixture. 
To assess benefits of a perfect chemical dispersant’s use, it must first be defined what suc 
cessful application should mean. In their simplified study focussing on modified drift paths 
Schwichtenberg et al. (2016) labelled application of a dispersant as successful if it reduced 
the amount of oil in the Wadden Sea by at least 95 %. Note that this definition is based on 
the amount of oil that would hit the coast without intervention rather than on the total amount 
of oil released. Consequently, the 100 % reference value could be a very small amount in 
absolute units. However, that only a small percentage of untreated oil hits the coast will occur 
rarely as in most cases the initial oil slick will not be spread too much (see the example in 
Figure 6.2). 
Figure 6.4 shows for each grid cell the probability that chemical dispersion would be benefi 
cial. Schwichtenberg et al. (2016) calculated these probabilities in terms of the fractions of 
the 2190 simulations during 2008-2014 for which the above criterion for success was met. 
Note that red areas, in which dispersants turned out to have little effects on the amount of oil 
that entered the Wadden Sea, occur for two different reasons. First, any reduction of Wad 
den Sea pollution (i.e. benefit from using a chemical dispersant) will be impossible if the 
Wadden Sea hadn’t been polluted anyway. This situation occurs in regions far from the 
coast. Second, the amount of oil entering coastal regions may be either not reduced or even 
increased. This latter situation underlies the red colouring of inshore regions. Examples, 
where suppressing wind forcing does not help or is even counterproductive, are when either 
dispersed oil can enter tidal basins with tidal currents or wind forcing acts in favour of coastal 
protection (i.e. winds blow offshore).