491
28.4 Lessons Learned During DWH Toxicity Testing
Toxicity testing of physically and chemically dispersed oil, and chemical dispersants following the DWH oil spill, expanded substantially our knowledge on the
biological responses of aquatic species to these complex chemical mixtures. Most
commonly, toxicity tests focused on standard aquatic species across several taxa
(e.g., mysid shrimp [Americamysis bahia]; inland silverside [Menidia beryllina];
EPA 2002) as standard testing protocols are well established including defined
internal controls (i.e., control survival) on which to base the quality of test results.
The overall assumption for using such species is that they provide conservative
toxicity estimates that can also be protective of untested species and sensitive life
stages. Although one of the drawbacks of using standard test species is that there are
uncertainties about how their sensitivity compares to that of a species of concern
(i.e., deep-sea and pelagic species), recent research supports the possible use of
standard test species as surrogates for deepwater species and is discussed in detail
in Ecotoxicology of Deep Ocean Spills (see Barron et al. 2020). However, for many
species of concern, laboratory husbandry and standard methods specific for each
species’ requirements may not be available, which was a clear challenge during the
DWH oil spill. Following the DWH oil spill, toxicity testing was performed using a
range of aquatic species (i.e., several taxa, habitat preferences), resulting in toxicity
test results for at least 20 different species, including standard test species. Test
results using species that had not previously been tested offered new insights into
their sensitivity relative to that of most commonly tested organisms. Based on the
information generated to date, early life stages (e.g., fish embryos) are generally
more sensitive to oil and dispersed oil than juveniles/adults of the same or related
species. These findings are not necessarily new but provide a means of confirming
earlier work. Similarly, the range of sensitivity of newly tested species appears to
fall within the range of sensitivity of most commonly tested species (Table 28.3).
The same finding applies to aquatic toxicity data from dispersant-only exposures
(Bejarano 2018).
Since a single measure of aquatic toxicity does not provide sufficient information
on which to infer protective thresholds, the concept of species sensitivity distributions (SSDs) has been recommended to facilitate evaluations of relative sensitivities
under comparable exposure conditions. Several studies (e.g., Bejarano et al. 2014;
Bejarano 2018; Barron et al. 2020) have shown that hazard concentrations from
SSDs may be protective of a wide range to species, including sensitive species. This
was recently demonstrated following a synthesis of dispersant-only toxicity data
(Bejarano 2018). While such approach works relatively well for single chemicals or
highly soluble chemical mixtures, there are a number of challenges when applied to
complex hydrocarbon mixtures such as crude oil. Interlaboratory comparisons of
species sensitivities based on toxicity test results with crude oil are difficult, unless
standard protocols are carefully followed (Coelho et al. 2013; Redman and Parkerton
2015). As a result, hazard concentrations from SSDs may not be appropriate, unless
toxicity data used in their development are from studies using comparable standard28 A Synthesis of DWH Oil: Chemical Dispersant and Chemically Dispersed Oil…
28.4 Lessons Learned During DWH Toxicity Testing
Toxicity testing of physically and chemically dispersed oil, and chemical dispersants following the DWH oil spill, expanded substantially our knowledge on the
biological responses of aquatic species to these complex chemical mixtures. Most
commonly, toxicity tests focused on standard aquatic species across several taxa
(e.g., mysid shrimp [Americamysis bahia]; inland silverside [Menidia beryllina];
EPA 2002) as standard testing protocols are well established including defined
internal controls (i.e., control survival) on which to base the quality of test results.
The overall assumption for using such species is that they provide conservative
toxicity estimates that can also be protective of untested species and sensitive life
stages. Although one of the drawbacks of using standard test species is that there are
uncertainties about how their sensitivity compares to that of a species of concern
(i.e., deep-sea and pelagic species), recent research supports the possible use of
standard test species as surrogates for deepwater species and is discussed in detail
in Ecotoxicology of Deep Ocean Spills (see Barron et al. 2020). However, for many
species of concern, laboratory husbandry and standard methods specific for each
species’ requirements may not be available, which was a clear challenge during the
DWH oil spill. Following the DWH oil spill, toxicity testing was performed using a
range of aquatic species (i.e., several taxa, habitat preferences), resulting in toxicity
test results for at least 20 different species, including standard test species. Test
results using species that had not previously been tested offered new insights into
their sensitivity relative to that of most commonly tested organisms. Based on the
information generated to date, early life stages (e.g., fish embryos) are generally
more sensitive to oil and dispersed oil than juveniles/adults of the same or related
species. These findings are not necessarily new but provide a means of confirming
earlier work. Similarly, the range of sensitivity of newly tested species appears to
fall within the range of sensitivity of most commonly tested species (Table 28.3).
The same finding applies to aquatic toxicity data from dispersant-only exposures
(Bejarano 2018).
Since a single measure of aquatic toxicity does not provide sufficient information
on which to infer protective thresholds, the concept of species sensitivity distributions (SSDs) has been recommended to facilitate evaluations of relative sensitivities
under comparable exposure conditions. Several studies (e.g., Bejarano et al. 2014;
Bejarano 2018; Barron et al. 2020) have shown that hazard concentrations from
SSDs may be protective of a wide range to species, including sensitive species. This
was recently demonstrated following a synthesis of dispersant-only toxicity data
(Bejarano 2018). While such approach works relatively well for single chemicals or
highly soluble chemical mixtures, there are a number of challenges when applied to
complex hydrocarbon mixtures such as crude oil. Interlaboratory comparisons of
species sensitivities based on toxicity test results with crude oil are difficult, unless
standard protocols are carefully followed (Coelho et al. 2013; Redman and Parkerton
2015). As a result, hazard concentrations from SSDs may not be appropriate, unless
toxicity data used in their development are from studies using comparable standard28 A Synthesis of DWH Oil: Chemical Dispersant and Chemically Dispersed Oil…