485
chronic tests are calculated for lethal concentrations (LCs), sublethal effect concentrations (ECs), concentrations that result in 25% inhibition in biological measurement (IC25s), no observed effect concentrations (NOECs), and lowest observed
effect concentrations (LOECs), using a variety of statistical approaches based on
point estimates (e.g., Probit or Spearman-Karber) or hypothesis (comparison)
methods.
Working with a complex mixture like crude oil with or without chemical dispersants poses many unique issues compared with single chemicals, with respect to test
exposure solution makeup and true organismal chemical exposure for reporting of
toxicity endpoints. These complexities and difficulties in preparing reproducible
standard test solutions were part of the motivation behind the establishment of
CROSERF which developed standardized robust oil toxicity testing methodology
(Singer et al. 1992; Singer et al. 2000, 2001a, b; Aurand and Coelho 2005). Prior to
DWH, various researchers and an NRC report discussed refinements to these protocols regarding the preparation and analysis of test media and interpretations from
toxicity tests (Barron and Ka’aihua 2003; NRC 2005). After DWH, standard operating procedures (SOPs) to conduct toxicity tests were developed by BP and NOAA/
trustees (Carney et al. 2016) based on CROSERF but included modifications, some
made prior to DWH but some made applying the unique conditions of this spill.
Deep-ocean, high-energy environments, which affect the environmental fate, transport, and physiochemical characteristics of the oil and dispersant, all had to be considered when designing toxicity exposure studies. For example, a high-energy WAF
preparation method (HEWAF; Carney et al. 2016; Forth et al. 2017a, b) was designed
to mimic the high-energy environment scenario occurring during the DWH event.
Many of these issues, including other nuances of working with oil and dispersants
and the pros and cons of various approaches (i.e., variable dilution/loading, sampling times, and type of analytical chemistry methods for exposure solutions), are
discussed in Modernizing Protocols for Aquatic Toxicity Testing of Oil and
Dispersant (see Mitchelmore et al. 2020) and summarized in Table 28.2.
28.2.3 Interpretation of Toxicity Test Results
There are inherent problems involved in the preparation of oil and water test solutions leading to widely varying bioavailable PAH concentrations limiting the utility
and interpretation of the observed effects if detailed chemical characterizations of
the exposure test solutions are not conducted. Using nominal oil concentrations or a
limited characterization of the test media is sadly still common – and never appropriate. This approach provides no useful data and is an unethical use of laboratory
organisms (vertebrate or invertebrate species). As described recently by Coelho
et al. (2013) and Bejarano et al. (2014), toxicity studies are useless without a detailed
understanding of true organismal exposure to oil.
The interpretation of toxicity tests is not just dependent on the composition of the
analytes (i.e., PAHs) but in what phase these compounds are found. This is
28 A Synthesis of DWH Oil: Chemical Dispersant and Chemically Dispersed Oil…
chronic tests are calculated for lethal concentrations (LCs), sublethal effect concentrations (ECs), concentrations that result in 25% inhibition in biological measurement (IC25s), no observed effect concentrations (NOECs), and lowest observed
effect concentrations (LOECs), using a variety of statistical approaches based on
point estimates (e.g., Probit or Spearman-Karber) or hypothesis (comparison)
methods.
Working with a complex mixture like crude oil with or without chemical dispersants poses many unique issues compared with single chemicals, with respect to test
exposure solution makeup and true organismal chemical exposure for reporting of
toxicity endpoints. These complexities and difficulties in preparing reproducible
standard test solutions were part of the motivation behind the establishment of
CROSERF which developed standardized robust oil toxicity testing methodology
(Singer et al. 1992; Singer et al. 2000, 2001a, b; Aurand and Coelho 2005). Prior to
DWH, various researchers and an NRC report discussed refinements to these protocols regarding the preparation and analysis of test media and interpretations from
toxicity tests (Barron and Ka’aihua 2003; NRC 2005). After DWH, standard operating procedures (SOPs) to conduct toxicity tests were developed by BP and NOAA/
trustees (Carney et al. 2016) based on CROSERF but included modifications, some
made prior to DWH but some made applying the unique conditions of this spill.
Deep-ocean, high-energy environments, which affect the environmental fate, transport, and physiochemical characteristics of the oil and dispersant, all had to be considered when designing toxicity exposure studies. For example, a high-energy WAF
preparation method (HEWAF; Carney et al. 2016; Forth et al. 2017a, b) was designed
to mimic the high-energy environment scenario occurring during the DWH event.
Many of these issues, including other nuances of working with oil and dispersants
and the pros and cons of various approaches (i.e., variable dilution/loading, sampling times, and type of analytical chemistry methods for exposure solutions), are
discussed in Modernizing Protocols for Aquatic Toxicity Testing of Oil and
Dispersant (see Mitchelmore et al. 2020) and summarized in Table 28.2.
28.2.3 Interpretation of Toxicity Test Results
There are inherent problems involved in the preparation of oil and water test solutions leading to widely varying bioavailable PAH concentrations limiting the utility
and interpretation of the observed effects if detailed chemical characterizations of
the exposure test solutions are not conducted. Using nominal oil concentrations or a
limited characterization of the test media is sadly still common – and never appropriate. This approach provides no useful data and is an unethical use of laboratory
organisms (vertebrate or invertebrate species). As described recently by Coelho
et al. (2013) and Bejarano et al. (2014), toxicity studies are useless without a detailed
understanding of true organismal exposure to oil.
The interpretation of toxicity tests is not just dependent on the composition of the
analytes (i.e., PAHs) but in what phase these compounds are found. This is
28 A Synthesis of DWH Oil: Chemical Dispersant and Chemically Dispersed Oil…