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27.3 Determining Toxicity to Aquatic Species from Deep
Ocean Spills
27.3.1 What Is Known about Deep Ocean Toxicity
Oil and gas exploration of the deep-sea environment have raised concerns about the
potential impact of deep ocean well blowouts on resources inhabiting these remote
areas of the ocean. Under a blowout spill scenario, oil exposures to deep-sea communities may occur through three pathways: (1) direct oil coating; (2) direct exposure to flocculated oil and oil residues deposited via marine snow; and (3) direct
exposure to oil droplets and dissolved hydrocarbon fractions. However, understanding the relative contribution of each exposure mechanism requires careful experimental design that may not be easily achievable. The field of aquatic toxicology has
primarily focused on understanding effects from oil spills under controlled laboratory exposures by means of water-accommodated fractions (WAF) with or without
dispersants (chemically enhanced water-accommodated fractions; CEWAF),
directly addressing the third exposure pathway.
The sensitivity of coastal aquatic species is relatively well understood compared
to the species and aquatic communities of the deep ocean and offshore environments. In particular, the sensitivity of larval and juvenile life stages of estuarine
organisms has been tested extensively in laboratory toxicity tests using a variety of
oil products (see Mitchelmore et al. 2020). Over 40 coastal species were tested during DWH and shown to be sensitive to weathered oil and field samples of spill water
(Echols et al. 2015; NOAA 2015). In recent years, several studies have emerged on
the relative sensitivity of select deep ocean species to single hydrocarbons, oil products, and dispersants. Knap et al. (2017) conducted toxicity testing of a single
hydrocarbon (1-methylnaphthalene) with the mysid shrimp (Americamysis bahia)
and five deep ocean crustacean species. Results based on lethal concentrations and
critical body burdens (CBB) indicated higher sensitivity of deep ocean species to
this petroleum component compared to other species. However, only two of the five
deep ocean crustaceans were more sensitive than the mysid shrimp, further supporting the possible use of this standard test species as a surrogate for deepwater species. Another study (McConville et al. 2018) evaluated the acute toxicity of several
petroleum compounds (i.e., toluene, 2-methylnaphthalene, phenanthrene) and mixtures (i.e., Corexit 9500, CEWAF of Alaskan North Slope crude oil) to sablefish
(Anoplopoma fimbria). Results showed that while this species has a sensitivity to
Corexit 9500 and CEWAF within the range reported for other fish species, it appears
to be more sensitive (based on CBB) than other aquatic species to single hydrocarbon compounds. Frometa et al. (2017) also found that the sensitivity of a deep ocean
gorgonian octocoral (Swiftia exserta) to Corexit 9500 was within the range of previously tested aquatic species. Although limited, exposure data for aromatic hydrocarbons, petroleum products, dispersants (Knap et al. 2017; McConville et al. 2018),
and even metals (Brown et al. 2017) suggest that the sensitivity of tested deep ocean
species falls within the range of traditionally tested species. Thus, euphotic zone
27 Ecotoxicology of Deep Ocean Spills
27.3 Determining Toxicity to Aquatic Species from Deep
Ocean Spills
27.3.1 What Is Known about Deep Ocean Toxicity
Oil and gas exploration of the deep-sea environment have raised concerns about the
potential impact of deep ocean well blowouts on resources inhabiting these remote
areas of the ocean. Under a blowout spill scenario, oil exposures to deep-sea communities may occur through three pathways: (1) direct oil coating; (2) direct exposure to flocculated oil and oil residues deposited via marine snow; and (3) direct
exposure to oil droplets and dissolved hydrocarbon fractions. However, understanding the relative contribution of each exposure mechanism requires careful experimental design that may not be easily achievable. The field of aquatic toxicology has
primarily focused on understanding effects from oil spills under controlled laboratory exposures by means of water-accommodated fractions (WAF) with or without
dispersants (chemically enhanced water-accommodated fractions; CEWAF),
directly addressing the third exposure pathway.
The sensitivity of coastal aquatic species is relatively well understood compared
to the species and aquatic communities of the deep ocean and offshore environments. In particular, the sensitivity of larval and juvenile life stages of estuarine
organisms has been tested extensively in laboratory toxicity tests using a variety of
oil products (see Mitchelmore et al. 2020). Over 40 coastal species were tested during DWH and shown to be sensitive to weathered oil and field samples of spill water
(Echols et al. 2015; NOAA 2015). In recent years, several studies have emerged on
the relative sensitivity of select deep ocean species to single hydrocarbons, oil products, and dispersants. Knap et al. (2017) conducted toxicity testing of a single
hydrocarbon (1-methylnaphthalene) with the mysid shrimp (Americamysis bahia)
and five deep ocean crustacean species. Results based on lethal concentrations and
critical body burdens (CBB) indicated higher sensitivity of deep ocean species to
this petroleum component compared to other species. However, only two of the five
deep ocean crustaceans were more sensitive than the mysid shrimp, further supporting the possible use of this standard test species as a surrogate for deepwater species. Another study (McConville et al. 2018) evaluated the acute toxicity of several
petroleum compounds (i.e., toluene, 2-methylnaphthalene, phenanthrene) and mixtures (i.e., Corexit 9500, CEWAF of Alaskan North Slope crude oil) to sablefish
(Anoplopoma fimbria). Results showed that while this species has a sensitivity to
Corexit 9500 and CEWAF within the range reported for other fish species, it appears
to be more sensitive (based on CBB) than other aquatic species to single hydrocarbon compounds. Frometa et al. (2017) also found that the sensitivity of a deep ocean
gorgonian octocoral (Swiftia exserta) to Corexit 9500 was within the range of previously tested aquatic species. Although limited, exposure data for aromatic hydrocarbons, petroleum products, dispersants (Knap et al. 2017; McConville et al. 2018),
and even metals (Brown et al. 2017) suggest that the sensitivity of tested deep ocean
species falls within the range of traditionally tested species. Thus, euphotic zone
27 Ecotoxicology of Deep Ocean Spills