587
mulations, primarily in short-duration acute exposure trials using model laboratory
species. The question of whether chemically dispersed oil is more toxic than dispersants or crude oil alone was evaluated, but issues with experimental protocols did
not allow a definitive resolution of this essential question. These analyses almost
exclusively used mortality-based toxic endpoints (e.g., LC 50 or lethal concentrations
resulting in 50% mortality to the species and life stage) being tested for shortduration (usually 96 h) exposures (NRC 2005).
The availability of baseline information on hydrocarbon and associated contaminants in water, sediments, and biota prior to DWH is important both for routine
monitoring impacts of drilling operations and for assessing impacts of small and
large accidental releases. Other than the NOAA Status and Trends (“Mussel Watch”)
program (Farrington et al. 2016), there were no organized, ongoing sentinel programs to collect contaminant data in a geographically synoptic fashion or over time,
prior to DWH. While there had been several studies of PAHs collected in the Gulf
of Mexico (GoM), most of these studies were site-specific (Santschi et al. 2001;
Mitra and Bianchi 2003; Overton et al. 2004; Iqbal et al. 2007), used to evaluate
issues such as near-field contaminant effects around oil and gas rigs and heavy
metal contamination arising from crude oil pollution (Peterson et al. 1996;
McDonald et al. 1996), evaluated impacts of produced water discharges in nearshore disposal (Boesch and Rabalais 1989), or assessed episodic large-scale contamination (Hom et al. 2008, following hurricane Katrina). More broadly, for some
large-scale tanker accidents, periodic post-spill evaluations of contaminant effects
and concentrations have been undertaken (e.g., Exxon Valdez, Rice et al. 1996), but
post-spill monitoring is the exception not the rule, and thus understanding “return to
baseline” when the pre-spill baselines were never established is problematic.
The GoM, as is the case with all oil-producing marine ecosystems, is subject to
hydrocarbon inputs from a variety of natural and anthropogenic sources. Natural
oil/gas seeps in the GoM account for the majority of oil inputs in most years, with
smaller quantities from accidental releases, vessel traffic, atmospheric deposition,
produced water discharges, riverine flows, and other sources. This oil “budget” is
important for context when oil contaminant baselines are estimated. Several estimates of oil budgets for the GoM and other coastal systems off the USA have been
developed (Ocean Studies Board and Marine Board 2003). Murawski et al. (2014)
estimated that the DWH accident accounted for over seven times the annual sum of
oil inputs from all other sources into the GoM, but that spill was confined to a portion of the northern Gulf, over about ¼ of the year. In coastal margins of the GoM,
there are no areas completely free of oil derivatives (Pulster et al. 2020), and thus
understanding spatial and temporal variation and trends in contaminant concentration baselines potentially allows attribution to the various sources contributing to
observed contamination rates. This is particularly salient using chronological sediment cores, which document time histories of such episodes in relation to human
and natural stressors.
Apart from the dynamics of ultra-deep spills, basic knowledge of the ecology of
the pelagic, mesopelagic, and bentho-pelagic environments where oil exploration
34 Summary of Progress on Major Research Issues: Deep-Sea Oil Spills
mulations, primarily in short-duration acute exposure trials using model laboratory
species. The question of whether chemically dispersed oil is more toxic than dispersants or crude oil alone was evaluated, but issues with experimental protocols did
not allow a definitive resolution of this essential question. These analyses almost
exclusively used mortality-based toxic endpoints (e.g., LC 50 or lethal concentrations
resulting in 50% mortality to the species and life stage) being tested for shortduration (usually 96 h) exposures (NRC 2005).
The availability of baseline information on hydrocarbon and associated contaminants in water, sediments, and biota prior to DWH is important both for routine
monitoring impacts of drilling operations and for assessing impacts of small and
large accidental releases. Other than the NOAA Status and Trends (“Mussel Watch”)
program (Farrington et al. 2016), there were no organized, ongoing sentinel programs to collect contaminant data in a geographically synoptic fashion or over time,
prior to DWH. While there had been several studies of PAHs collected in the Gulf
of Mexico (GoM), most of these studies were site-specific (Santschi et al. 2001;
Mitra and Bianchi 2003; Overton et al. 2004; Iqbal et al. 2007), used to evaluate
issues such as near-field contaminant effects around oil and gas rigs and heavy
metal contamination arising from crude oil pollution (Peterson et al. 1996;
McDonald et al. 1996), evaluated impacts of produced water discharges in nearshore disposal (Boesch and Rabalais 1989), or assessed episodic large-scale contamination (Hom et al. 2008, following hurricane Katrina). More broadly, for some
large-scale tanker accidents, periodic post-spill evaluations of contaminant effects
and concentrations have been undertaken (e.g., Exxon Valdez, Rice et al. 1996), but
post-spill monitoring is the exception not the rule, and thus understanding “return to
baseline” when the pre-spill baselines were never established is problematic.
The GoM, as is the case with all oil-producing marine ecosystems, is subject to
hydrocarbon inputs from a variety of natural and anthropogenic sources. Natural
oil/gas seeps in the GoM account for the majority of oil inputs in most years, with
smaller quantities from accidental releases, vessel traffic, atmospheric deposition,
produced water discharges, riverine flows, and other sources. This oil “budget” is
important for context when oil contaminant baselines are estimated. Several estimates of oil budgets for the GoM and other coastal systems off the USA have been
developed (Ocean Studies Board and Marine Board 2003). Murawski et al. (2014)
estimated that the DWH accident accounted for over seven times the annual sum of
oil inputs from all other sources into the GoM, but that spill was confined to a portion of the northern Gulf, over about ¼ of the year. In coastal margins of the GoM,
there are no areas completely free of oil derivatives (Pulster et al. 2020), and thus
understanding spatial and temporal variation and trends in contaminant concentration baselines potentially allows attribution to the various sources contributing to
observed contamination rates. This is particularly salient using chronological sediment cores, which document time histories of such episodes in relation to human
and natural stressors.
Apart from the dynamics of ultra-deep spills, basic knowledge of the ecology of
the pelagic, mesopelagic, and bentho-pelagic environments where oil exploration
34 Summary of Progress on Major Research Issues: Deep-Sea Oil Spills