BfR-Wissenschaft 
51 
The processes, distribution, fate and degradation of oil and dispersants are not fully under 
stood. For the dispersant application in the Gulf of Mexico it is presumed that the formation of 
the oil plumes was intensified by the underwater application of dispersants. To learn more 
about where the Corexit finally ended up, researchers used the component DOSS (dioctyl 
sodium sulfosuccinate) to trace the dispersant (Kujawinski et al. 2011). 
The oil spill covered up to 75 000 km 2 of the sea surface and approximately 2000 km of coast 
were affected. Due to the weathering of the oil and other processes the non-volatile not 
quickly degraded oil compounds from the water surface and the water column are sinking on 
the sea bottom. David et al. (2014) identified a region of at least 3200 km 2 of sea bottom that 
was covered with oil from the Macondo Well. From the seabed the oil can be partly incorpo 
rated into the sediment. Five years after the incident the oil from Macondo well is still found in 
or on the seabed. Estimations assume more than 380 000 tons of oil are still in the environ 
ment. These depositions can be resuspended. Especially after hurricanes and storm events 
tar balls were found at the beaches. 
Adverse impact on the environment and its recovery 
Adverse effects on various species from different trophic levels were measured in the various 
monitoring projects e.g. for invertebrates, corals, shellfish, fish, birds and marine mammals. 
The impact of the oil can be divided in immediate (acute) effects and long-term (chronic) ef 
fects. Acute effects can comprise general unspecific toxic effects potentially leading to sub 
sequent lethal effects, consequences of physical effects (oiling of organisms), which may 
lead to loss of buoyancy and thermal insulation, or internal inflammation and bleeding result 
ing from the ingestion of oil. Chronic effects can comprise direct long-term toxic effects such 
as reproduction inhibition or indirect effects resulting from modified food supply due to effect 
on other species in the food chain. Due to the fact, that many organisms of higher trophic 
level have lower reproduction rates, the consequences on the marine populations are cur 
rently not completely assessable. The same is valid for deep sea species, which live in lower 
temperatures and therefore have much lower metabolic rates and reproduction. The influ 
ence of the big amount of oil with its toxicity and also its organic load on the deep sea envi 
ronment and its food web is today largely unknown. The same applies to the long-termed 
effects of the dispersants on the whole marine ecosystem. 
Human health issues and operational aspects 
It has been reported that up to 200.000 people were having health issues due to the Deep 
water Florizon incident. The health issues range from skin problems, respiratory symptoms to 
mental disorders with depressions and distress. Partly these issues could have been pre 
vented by the proper use of personal protective equipment (PPE) and adequate safety train 
ing for the potentially endangered staff. Hence these aspects should be taken into account 
when planning dispersant application involving the public and the locally deployed oil spill 
combating units. Anyway, it was a novelty, that dispersants were applied in spill operations 
under mission-tactical reasons to reduce the atmospheric load with volatile organic com 
pounds. 
Conclusions 
The Deepwater Horizon incident has initiated an intensive debate over the usage of disper 
sants. Many research programs are still running and a lot of the results are still not published 
- or they are not publicly accessible today. The adverse effects of the Deepwater Horizon oil 
spill on the environment and the biocoenosis are still measurable - and further impairment 
can be assumed, since the spilled oil only partly degraded and to date can be found in the 
environment. Five years of monitoring and research are too short to determine the long-term