Geo-Mar Lett (2017) 37:163-170 
169 
Ö Springer 
surface oil slick reduces the toxicity of dispersed oil. These 
constituents tend to evaporate already within the first hours 
after an oil spill incident, so that French-McCay and Payne 
(2001) found toxicities of oil-dispersant mixtures to be con 
siderably higher if dispersants were used within the first 6 h. 
For logistic reasons, however, an application of dispersants 
within the first few hours is difficult anyway. 
Even if a pollutant cannot be prevented from reaching the 
coast, in most cases its arrival would be much delayed by a 
(perfect) dispersant’s use (Fig. 3). As dispersed oil is no longer 
accessible for mechanical cleaning, the benefit would not be a 
gain of additional time for taking mechanical response mea 
sures but rather a better chance for dilution and microbiolog 
ical degradation. Furthermore, the latter processes are also 
more active for oil-dispersant mixtures than for untreated oil 
slicks (Lee et al. 2011). 
Some generalizations of this study are conceivable. 
Regarding the assumption of a 100% effective dispersant, re 
sults of the two alternative simulations with untreated and 
100% chemically dispersed oil could be combined with 
weighting factors based on expert knowledge on the efficacy 
of the dispersant under given environmental conditions (tem 
perature, salinity, wave energy). The definition of environ 
mental harmfulness adopted in this study is very simple; an 
oil slick is assumed to produce substantial damages only if it 
enters a coastal basin. Switching to a concept based on water 
depth and its potential for dilution (cf. Le Floch et al. 2014) 
would be straightforward. For many practical applications, 
detailed maps of sensitive habitats or communities of endan 
gered birds exist (e.g. Koffijberg et al. 2003; Garthe et al. 
2012). This additional information must obviously be taken 
into account. Figure 2 of the present study, concentrating on 
modified drift behaviour, establishes a basis for performing 
such a fully fledged precautionary NEBA related to the appli 
cation of chemical dispersants in German coastal areas. 
Conclusions 
In Germany the use of chemical dispersants for combating oil 
spills in coastal areas is understood only as a last resort. The 
discussion often focuses on aspects of technical applicability, 
efficacy and toxicity. Flowever, another key criterion for deci 
sions on the potential use of dispersants should be whether 
winds are expected to act in favour or to the disadvantage of 
coastal protection. The probabilistic map produced in the pres 
ent study identifies areas where the chances that chemical 
dispersant application would keep a pollutant out of vulnera 
ble tidal basins are particularly high. These areas were found 
to strongly overlap with nearshore regions between 10 m and 
20 m water depth. A detailed site-specific NEBA particularly 
for such areas would be the logical next step to ensure that no 
negative side effects counteract expected benefits from 
modified drift behaviour. Comprehensive monitoring of sea 
bed habitats and communities is obviously an indispensable 
prerequisite for that purpose. 
While winds and currents are reliably represented by 
model-based reconstructions, the analysis in this study 
disregarded many aspects that are definitely highly relevant 
for practical decision making but depend on details of the 
specific accident that occurred. The type of oil spilled, for 
instance, determines both oil weathering and the efficacy of 
the dispersant applied. But even when such details are known 
in advance, values of process-related parameters in corre 
sponding simulations would still be highly uncertain. 
It is argued that for any real accident, already using two 
idealized simulations with either undispersed or frilly dis 
persed oil provides a useful pragmatic approach to delineate 
the corridor of possible developments and regions possibly 
endangered. Doubts how to properly weight the two extreme 
cases reflect inevitable uncertainty with regard to the strength 
of weathering and dispersant efficacy. Pressed for time, expert 
experience and available evidence is needed to build a basis 
for reasonable decisions. 
Acknowledgements The research was funded by the WIMO project 
supported by two ministries in Lower Saxony: the “Ministerium fur 
Umwelt, Energie und Klimaschutz” as well as the “Ministerium fur 
Wissenschaft und Kultur”. We would like to thank Ulrike Kleeberg for 
help with GIS applications and Carlo van Bemem for constmctive dis 
cussions. The article benefitted from constructive assessments by M.G. 
Hadfield and an anonymous reviewer. 
Compliance with ethical standards 
Conflict of interest The authors declare that there is no conflict of 
interest with third parties. 
Open Access This article is distributed under the terms of the Creative 
Commons Attribution 4.0 International License (http:// 
creativecommons.org/licenses/by/4.0/), which permits unrestricted use, 
distribution, and reproduction in any medium, provided you give appro 
priate credit to the original author(s) and the source, provide a link to the 
Creative Commons license, and indicate if changes were made. 
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