BfR-Wissenschaft
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The processes, distribution, fate and degradation of oil and dispersants are not fully understood.
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 incorporated
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 environment.
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) effects.
Acute effects can comprise general unspecific toxic effects potentially leading to subsequent
lethal effects, consequences of physical effects (oiling of organisms), which may
lead to loss of buoyancy and thermal insulation, or internal inflammation and bleeding resulting
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 currently
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 influence
of the big amount of oil with its toxicity and also its organic load on the deep sea environment
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 Deepwater
Florizon incident. The health issues range from skin problems, respiratory symptoms to
mental disorders with depressions and distress. Partly these issues could have been prevented
by the proper use of personal protective equipment (PPE) and adequate safety training
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 compounds.
Conclusions
The Deepwater Horizon incident has initiated an intensive debate over the usage of dispersants.
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
