167
well as the behavior of the organisms (Tamis et al. 2012). Different laboratory tests
are available simulating various exposure regimes (Redman and Parkerton 2015),
yet these may not necessarily match exposure regimes at sea.
In addition to chemical dispersion aiming to “dilute” the pollutant quicker, it is
also considered to enhance biodegradation of the suspended oil. The role of biodegradation in natural and chemically dispersed oil is unclear. Theoretically dispersed
oil is more bioavailable, but bacteria may also experience more acute toxic effects
(Rahsepar et al. 2016). Conditions are heterogenic in space and time and difficult to
replicate in a laboratory. As a result, conflicting information is available indicating
either biodegradation is enhanced, decreased, or indifferent of chemical dispersion
(Lee et al. 2013; Kleindienst et al. 2016; Rahsepar et al. 2016).
10.4.2.2 Benthic
Dispersed oil can also reconcentrate on the seafloor, either as a result of suspended
sediments adhering to oil droplets and sinking (Khelifa et al. 2008) or via the
observed so-called MOSSFA mechanism (Marine Oil Snow Sedimentation and
Flocculent Accumulation). This effect is enhanced in situations with phytoplankton
blooms combined with particulate matter in the water column (Vonk et al. 2015;
Daly et al. 2016; van Eenennaam et al. 2016). This MOSSFA could cause longlasting effects as the oil will be concentrated on/in the sediment followed by reduced
biodegradation under oxygen-limited conditions (Langenhoff et al. 2020) and may
cause prolonged local exposure to hydrocarbons (Lee et al. 2015). This applies even
more so for “marine oil snow,” which was found to cause more adverse effects in
benthic invertebrates than oil-sediment aggregates (van Eenennaam et al. 2018;
Schwing et al. 2020).
10.5 Concluding Remarks
The notion that dispersants should not be applied if their effectiveness is unsure
stands to reason. Apart from the limited cost-effectiveness in such a case, the resulting change in oil properties can hamper effectiveness of mechanical removal methods (ITOPF 2012).
However, for a given spill situation, if we can prove that addition of dispersants
can successfully mitigate potential for effects on the water surface and coastlines, as
well as demonstrate that risks for adverse effects in other compartments are acceptable, dispersants provide a useful response strategy that can work in conditions
where other methods are unsuccessful.
Acknowledgments This research was made possible by a from the Gulf of Mexico Research
Initiative/C-IMAGE. Data are publicly available through the Gulf of Mexico Research Initiative
Information and Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org/
(doi:10.7266/n7-8hmm-kx37).
10 Effects of Oil Properties and Slick Thickness on Dispersant Field Effectiveness…
well as the behavior of the organisms (Tamis et al. 2012). Different laboratory tests
are available simulating various exposure regimes (Redman and Parkerton 2015),
yet these may not necessarily match exposure regimes at sea.
In addition to chemical dispersion aiming to “dilute” the pollutant quicker, it is
also considered to enhance biodegradation of the suspended oil. The role of biodegradation in natural and chemically dispersed oil is unclear. Theoretically dispersed
oil is more bioavailable, but bacteria may also experience more acute toxic effects
(Rahsepar et al. 2016). Conditions are heterogenic in space and time and difficult to
replicate in a laboratory. As a result, conflicting information is available indicating
either biodegradation is enhanced, decreased, or indifferent of chemical dispersion
(Lee et al. 2013; Kleindienst et al. 2016; Rahsepar et al. 2016).
10.4.2.2 Benthic
Dispersed oil can also reconcentrate on the seafloor, either as a result of suspended
sediments adhering to oil droplets and sinking (Khelifa et al. 2008) or via the
observed so-called MOSSFA mechanism (Marine Oil Snow Sedimentation and
Flocculent Accumulation). This effect is enhanced in situations with phytoplankton
blooms combined with particulate matter in the water column (Vonk et al. 2015;
Daly et al. 2016; van Eenennaam et al. 2016). This MOSSFA could cause longlasting effects as the oil will be concentrated on/in the sediment followed by reduced
biodegradation under oxygen-limited conditions (Langenhoff et al. 2020) and may
cause prolonged local exposure to hydrocarbons (Lee et al. 2015). This applies even
more so for “marine oil snow,” which was found to cause more adverse effects in
benthic invertebrates than oil-sediment aggregates (van Eenennaam et al. 2018;
Schwing et al. 2020).
10.5 Concluding Remarks
The notion that dispersants should not be applied if their effectiveness is unsure
stands to reason. Apart from the limited cost-effectiveness in such a case, the resulting change in oil properties can hamper effectiveness of mechanical removal methods (ITOPF 2012).
However, for a given spill situation, if we can prove that addition of dispersants
can successfully mitigate potential for effects on the water surface and coastlines, as
well as demonstrate that risks for adverse effects in other compartments are acceptable, dispersants provide a useful response strategy that can work in conditions
where other methods are unsuccessful.
Acknowledgments This research was made possible by a from the Gulf of Mexico Research
Initiative/C-IMAGE. Data are publicly available through the Gulf of Mexico Research Initiative
Information and Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org/
(doi:10.7266/n7-8hmm-kx37).
10 Effects of Oil Properties and Slick Thickness on Dispersant Field Effectiveness…