302
However, during the immediate release of the dispersed oil, volatile hydrocarbons
including some of the more toxic compounds of benzene, toluene, ethylbenzene,
and xylenes (BTEX) can inhibit the oil degradation (Sherry et al., Front Microbiol
5:131, 2014).
Depending on the oceanic conditions, the addition of chemical dispersants can
result in excessive formation of marine snow. It has been shown that the application
of dispersants during phytoplankton blooms can trigger the formation of marine
snow to which the sticky dispersed oil can bind. In the presence of mineral particles,
oiled snow complexes are being formed that become negatively buoyant and sink to
the ocean floor. As a result, oiled marine snow accumulates on the ocean floor where
biodegradation is inhibited due to oxygen depletion.
The abovementioned two mechanisms of inhibition of oil biodegradation upon
application of oil spill dispersants will be discussed in this chapter.
Keywords Biodegradation · Marine snow · Oil spill · Sediment · MOSSFA ·
Deepwater Horizon oil spill · Dispersants · Enhanced dissolution
18.1 Introduction
After an oil spill, various responses are possible, stopping the flow, containing the
oil, and removal of oil from the sea surface (Fingas 2011). Methods to remove and
prevent spreading of the spilled oil involve skimming, in situ burning, or the addition of chemical dispersants. Dispersant application was one of the responses during
the Deepwater Horizon (DWH) oil spill, when ~640 million liters (4 million barrels) of oil were released into the northern Gulf of Mexico (GoM) over a period of
almost 3 months. Around 8 million liters of the chemical dispersants Corexit 9527
and Corexit 9500A were added to the water surface or injected into the wellhead at
a depth of 1500 m (Kujawinski et al. 2011; Brooks et al. 2015), the first time dispersants were used at both spots. Chemical dispersants reduce the interfacial tension
between oil and water, stabilize the smaller oil droplets that are formed, and stimulate the dissolution of the more hydrophilic and toxic oil compounds (Brooks et al.
2015). Smaller droplet sizes provide a larger surface area for oil-degrading bacteria
(Lessard and DeMarco 2000), thus increasing the bioavailability of oil. Subsequently,
this can enhance the biodegradability of the dispersed oil. As a result, the number
and activity of oil-degrading bacteria can increase, and more oil will be degraded in
a shorter period of time (Kessler et al. 2011). These are the underlying mechanisms
by which chemical dispersants enhance oil biodegradation.
There was an additional effect observed during the DWH oil spill following the
application of chemical dispersants. The application of dispersants in the northern
GoM triggered the formation of flocculent material and sinking of marine snow
(biological debris) during the spring phytoplankton bloom, as a biological stress
response to dispersants and oil (Passow et al. 2012; Van Eenennaam et al. 2016;
Ziervogel et al. 2012, 2016). This has been reported previously (Vonk et al. 2015).
A. A. M. Langenhoff et al.
However, during the immediate release of the dispersed oil, volatile hydrocarbons
including some of the more toxic compounds of benzene, toluene, ethylbenzene,
and xylenes (BTEX) can inhibit the oil degradation (Sherry et al., Front Microbiol
5:131, 2014).
Depending on the oceanic conditions, the addition of chemical dispersants can
result in excessive formation of marine snow. It has been shown that the application
of dispersants during phytoplankton blooms can trigger the formation of marine
snow to which the sticky dispersed oil can bind. In the presence of mineral particles,
oiled snow complexes are being formed that become negatively buoyant and sink to
the ocean floor. As a result, oiled marine snow accumulates on the ocean floor where
biodegradation is inhibited due to oxygen depletion.
The abovementioned two mechanisms of inhibition of oil biodegradation upon
application of oil spill dispersants will be discussed in this chapter.
Keywords Biodegradation · Marine snow · Oil spill · Sediment · MOSSFA ·
Deepwater Horizon oil spill · Dispersants · Enhanced dissolution
18.1 Introduction
After an oil spill, various responses are possible, stopping the flow, containing the
oil, and removal of oil from the sea surface (Fingas 2011). Methods to remove and
prevent spreading of the spilled oil involve skimming, in situ burning, or the addition of chemical dispersants. Dispersant application was one of the responses during
the Deepwater Horizon (DWH) oil spill, when ~640 million liters (4 million barrels) of oil were released into the northern Gulf of Mexico (GoM) over a period of
almost 3 months. Around 8 million liters of the chemical dispersants Corexit 9527
and Corexit 9500A were added to the water surface or injected into the wellhead at
a depth of 1500 m (Kujawinski et al. 2011; Brooks et al. 2015), the first time dispersants were used at both spots. Chemical dispersants reduce the interfacial tension
between oil and water, stabilize the smaller oil droplets that are formed, and stimulate the dissolution of the more hydrophilic and toxic oil compounds (Brooks et al.
2015). Smaller droplet sizes provide a larger surface area for oil-degrading bacteria
(Lessard and DeMarco 2000), thus increasing the bioavailability of oil. Subsequently,
this can enhance the biodegradability of the dispersed oil. As a result, the number
and activity of oil-degrading bacteria can increase, and more oil will be degraded in
a shorter period of time (Kessler et al. 2011). These are the underlying mechanisms
by which chemical dispersants enhance oil biodegradation.
There was an additional effect observed during the DWH oil spill following the
application of chemical dispersants. The application of dispersants in the northern
GoM triggered the formation of flocculent material and sinking of marine snow
(biological debris) during the spring phytoplankton bloom, as a biological stress
response to dispersants and oil (Passow et al. 2012; Van Eenennaam et al. 2016;
Ziervogel et al. 2012, 2016). This has been reported previously (Vonk et al. 2015).
A. A. M. Langenhoff et al.