The Use of Dispersants in Marine Oil Spill Response (2020) / Chapter Skim
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3 AQUATIC TOXICOLOGY AND BIOLOGICAL EFFECTS
3 AQUATIC TOXICOLOGY AND BIOLOGICAL EFFECTS
Pages 67-114
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From page 67... ...
oil spill (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016; Jones, 2010)
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From page 68... ...
These key considerations for assessing the toxicity of oil spills in relation to oil and dispersed oil are illustrated in Figure 3.1. Aquatic organisms were potentially exposed to physically- and chemically-dispersed oil due to the formation of deepwater plumes, to surface dispersed oil, and from rising and surfaced oil.
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From page 69... ...
Because of the challenges in differentiating the biological effects of an oil spill with and without dispersant use under field conditions, the primary focus of this chapter is on aquatic toxicity as determined using laboratory tests. Finally, it provides context of toxicity in relation to observed field exposures and discusses potential future advances in the field of oil and dispersed oil toxicity testing.
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From page 70... ...
The primary goal of this evaluation is to address the central question of whether exposure media containing chemically dispersed oil is more or less toxic than is exposure media containing physically dispersed oil, and to demonstrate challenges in interpreting toxicity data which were previously limited (NRC, 1989, 2005) by the availability of quantitative information.
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From page 71... ...
Variable Dilution -- Toxicity tests of WAF or CEWAF performed with oil doses derived from a dilution series of a stock WAF prepared at a single high oil loading. Variable Loading -- Toxicity tests performed using individually prepared WAFs or CEWAFs with an increasing amount of oil added to the aqueous phase.
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From page 72... ...
The most typically reported endpoint, primarily from acute toxicity tests, is the LC50, or the median lethal concentration that causes death to 50% of the exposed organisms at a specific exposure duration (i.e., 96-hour LC50)
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From page 73... ...
, is whether the toxicity and exposure potential of untreated oil are less than or greater than that of dispersed oil under actual field conditions and in laboratory toxicity investigations. Measuring the Toxicity of Oil Determining the toxicity of oil from aquatic exposures for both physically and chemically dispersed oil is complicated not only by the idiosyncrasies of test conditions used in most studies
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From page 74... ...
and the method for preparing the concentration series for the WAFs to be tested have the potential to influence the presence, concentration, and size of microdroplets. These definitions are used in the following section: Dissolved Concentrations -- the concentration of oil components in only the aqueous phase.
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From page 75... ...
Method for Creating a Concentration Series: The Effects of Microdroplets Two different methods have commonly been used to create exposure treatments for toxicity tests: variable loading and variable dilution (NRC, 2005)
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From page 76... ...
The dissolved concentrations are measured from filtered samples. The concentrations are the arithmetic sum of the polycyclic aromatic hydrocarbons (PAHs)
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From page 77... ...
However, a more detailed investigation is required in order to separate these effects more reliably. The advantage of the variable loading method when creating test solutions is that it provides an initial answer to the central question posed in this chapter: whether exposure media containing chemically dispersed oil is more or less toxic than exposure media containing physically dispersed oil.
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From page 78... ...
The reason why is that when the WAF is initially diluted the dissolved concentrations of the oil components decrease. This disrupts the equilibrium between the microdroplet oil and aqueous phases in (B)
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From page 79... ...
are adopted as the exposure metric. Because there are many individual oil components in the aqueous phase, a "concentration" needs to be defined.
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From page 80... ...
This point is discussed further later in the chapter. It is clear from these results that these toxicity data in their present form cannot be used to determine if exposure media containing chemically dispersed oil is more or less toxic than that containing physically dispersed oil.
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From page 81... ...
: Measured TPAH50 concentrations in water samples with paired unfiltered (total concentration) and filtered (dissolved concentrations)
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From page 82... ...
Estimation of toxicity values from variable dilution preparations should only be made based on analyses on filtered samples at each dilution and not solely on unfiltered samples in WAF stock, as is often the case for standard toxicity testing. As an example of the difficulty of interpreting data, a study with early life stages of mahimahi found that the acute toxicity of CEWAF was higher than in HEWAF when comparisons were based on TPAH total concentrations, while their toxicities were comparable based on dissolved concentrations of TPAHs and 3-ring PAHs (Esbaugh et al., 2016)
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From page 83... ...
Understanding the toxicity of oil is complicated due to the nature of oil and its behavior in WAFs. The problems outlined above can only be addressed quantitatively using a model of the toxicity of oil that explicitly includes the processes that influence the distribution of components between the oil and aqueous phases and includes an appropriate aggregate dose metric that deals appropriately with the fact that individual components have widely differing toxicity.
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From page 84... ...
microdroplets world mixing energies WAF blender with 120 sec blend and 1 hr settle Variable dilution Solution derived from a single oil Standard stock solution Dissolution of oil method and water mixture (stock solution) prepared once at initiation components from from which dilutions are prepared of experiments microdroplets results in changing concentrations of dissolved oil components Variable loading Individual test solutions Multiple test solutions are This dissolved concentration method are prepared using variable prepared instead of one is the same with and without concentrations (loadings)
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From page 85... ...
from of oil spills and contribute (dissolved/ glass wool and 1µm GF/F and 0.7 test media thereby allowing to the overall exposure particulate GF/F2 under gentle vacuum and interpretation of toxicity to burden phases) analysis of filtrate and non-filtered dissolved oil test solutions Quantitation of Recommend analysis of size and Allows complete Difficult to understand droplets distribution interpretation of oil in the relative contributions both droplet and dissolved of droplets and dissolved manifestations components in mixtures NOTE: Modified from original table proposed by Mitchelmore et al., 2020.
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From page 86... ...
. Toxicity of Mixtures: Toxic Units The soluble oil components contribute to aquatic toxicity to variable degrees, and a model is needed to quantify the toxicity of mixtures.
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From page 87... ...
3. The TLM is used to compute the LC50 for acute toxicity or for chronic toxicity using the ACR, as described above, for each of the dissolved concentrations.
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From page 88... ...
The TUs are based on dissolved concentrations. The acute HC5 critical body burden required for the calculation is from McGrath et al., 2018.
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From page 89... ...
The comparison below considers the toxicity of an aqueous phase WAF in equilibrium with a large enough oil loading to ensure that the oil composition is not significantly altered by the dissolution of the oil components into the aqueous phase once equilibrium has been achieved. The resulting saturated aqueous phase has the highest dissolved concentrations that can exist for this oil.
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From page 90... ...
EqiTox (TU) Acenaphthene 3.878 0.269 41.5 10.375 0.250 Anthracene 4.546 0.0633 11.3 2.825 0.250 Pyrene 5.126 0.018 3.64 0.910 0.250 Chrysene 5.782 0.00434 0.99 0.248 0.250 TPAH TU Sum 14.358 1.000 FIGURE 3.10 The total acute HC5 TU concentrations TUT , and the TU concentrations of the TPAH components for saturated WAF, computed at total oil loading = 10 g/L.
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From page 91... ...
They are not a constant multiple of the actual TU concentration. Their use as dose metrics for toxicity tests at different total oil concentrations can lead to incorrect FIGURE 3.11 (A)
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From page 92... ...
of the total dissolved oil concentrations resulting from the minimization of oil droplet interference by mixing the exposure media without promoting microdroplet formations. In contrast, the percent dissolved for CEWAF and HEWAF are a smaller percentage of the total dissolved concentrations (below ~20% and ~5%, respectively)
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From page 93... ...
Effect of Microdroplets on Dissolved Concentrations in Variable Dilution Media The failure of the variable dilution toxicity test to determine whether the addition of dispersant increased or decreased the toxicity of the exposure media containing oil (as shown in Figure 3.7) is attributed to the influence of microdroplets.
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From page 94... ...
The designation of acute versus chronic toxicity testing differentiates between shorter and longer exposure times. The variations in exposure times and concentrations can be extreme during oil spills.
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From page 95... ...
Toxicity tests that are designed to augment the available data for shorter exposure periods could be used to estimate HC5s for exposure times less than the available 96-hour HC5. Phototoxicity The fact that exposure to solar radiation increases the toxicity of certain PAHs in mammalian species has been known for more than 80 years (Findlay, 1928)
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From page 96... ...
A model that addresses each of these processes is the Phototoxic Target Lipid Model (Marzooghi et al., 2017) , which is based on the TLM used in PETROTOX.
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From page 97... ...
20 15 NOTE: ANI = average number of Artemia salina nauplii immobilized; HOMO-LUMO gap = difference in energy between the highest occupied molecular orbital and the lowest unoccupied molecular orbital; LC50 = lethal concentration at 50% mortality; LT50 = lethal time at 50% mortality; RPA = relative phototoxic activity; UV = ultraviolet; VIS = visible. aFactor accounting for the difference between organism sensitivities.
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From page 98... ...
For an application of dispersant to a surface spill, the dispersant would increase the dissolved concentrations. The dispersed oil droplets would be mixed into the top few meters, and PAHs would dissolve from the droplets to increase the aqueous concentrations.
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From page 99... ...
. As a consequence, the dose metric employed for sediment toxicity tests must account for this.
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From page 100... ...
. It has been applied by EPA in the initial evaluation of sediment toxicity for the DWH oil spill (EPA, 2010, 2016a,b)
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From page 101... ...
AQUATIC TOXICOLOGY AND BIOLOGICAL EFFECTS 101 FIGUREFigureComparison of chronic HC5 concentrations to observed TPAH concentrations. Caption reads: 3.18 3.18 "Graphs showing the concentrations of TPAH50 in 2010/2011 cores containing wax-rich, severely weathered Macondo oil at the surface versus sediment depth for cores (A)
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From page 102... ...
These correspond to approximately dissolved TPAH concentrations of 10 and 0.5 mg TPAH/L FIGURE 3.19 Compilation of DWH water column TPAH concentrations. Figure caption reads: "Total polycyclic aromatic hydrocarbon (TPAH)
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From page 103... ...
have an effect on the composition of hydrocarbons in the exposure media, thus influencing their toxicity. Consequently, the comparability and reproducibility of toxicity data, as well as their practical application to spill situations, require the consistent use of standardized test procedures.
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From page 104... ...
• Analyze unfiltered and filtered water samples or passive sampling of the dissolved concentration of each test solution to account for relative contribution of microdroplets. • If the variable loading method is adopted, develop and standardize analytical protocols that focus on dissolved oil exposures (e.g., filtering or passive sampling)
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From page 105... ...
BIOLOGICAL EFFECTS The exposure of aquatic species to the toxic fractions in oil under field conditions depends on the rate at which petroleum hydrocarbons partition and dilute into the water column, with a greater petroleum hydrocarbon exposure potentially resulting from the use of chemical dispersants, although the combination of dilution, dispersion, and biodegradation serves to reduce aqueous concentrations significantly and rapidly. Slow moving or immobile aquatic species and life stages that are entrained within water masses containing physically and/or chemically dispersed oil may be at greater risk of exposure to dissolved oil fractions.
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From page 106... ...
• "Because mixture interactions are not well studied, TPAH concentrations 0.1 µg/L following oil spills should be considered hazardous." The use of TPAH concentrations as the dose metric is not consistent with the large variation in toxicity of the individual PAHs. The only currently available experimentally validated mixture model is TUs.
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From page 107... ...
As a point of reference, 75% of water samples collected during the DWH oil spill had TPAH concentrations (sum of 50 parent and alkylated PAHs) of < 1 µg/L, though water samples in the vicinity of the wellhead had concentrations > 1,000 µg/L (Boehm et al., 2016; see Figure 3.19)
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From page 108... ...
It is thus important to consider sublethal impacts, including those directly related to population vital rates, when considering the effects of toxic exposures from the population life cycle perspective. For more than 20 years, there has been concern that if oil spills (and other toxic substances)
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From page 109... ...
Despite this potential reduction in exposure to volatile compounds, the hazard posed by dispersant use to wildlife under field conditions is not fully understood because it is difficult to differentiate the impacts of chemically dispersed oil from those of physically dispersed oil. Most of the current knowledge on oil spill impacts to wildlife has been generated through controlled laboratory exposures or from real-world incidents that did not involve the use of dispersants.
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From page 110... ...
. For example, following the Ixtoc I and DWH oil spills, large numbers of sea turtles were found to have oil in their oral and nasal cavities and in their digestive tracts (Hall et al., 1983; Mitchelmore et al., 2017)
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From page 111... ...
New scientific information has been generated through the NRDA process from multiple prior oil spills. To support injury assessments and damage quantification, NRDA generates information using reproducible standard scientific approaches, which often involve toxicity testing under controlled laboratory conditions.
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From page 112... ...
The database enables users to filter information that specifically relates to a particular oil or dispersant, which allows decision makers to rapidly access past research and apply it in a meaningful way. From a practical perspective, the use of SSDs is advantageous because: • SSDs provide potentially useful information to stakeholders involved in oil spill response decision making.
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From page 113... ...
is the only presently available, scientifically sound dose metric. Finding: Toxicity tests using variable dilution cannot be used to determine if exposure media containing dispersed oil is more or less toxic than is the exposure media containing untreated oil, because (1)
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From page 114... ...
Characterizing these oils into a manageable number of hydrocarbon blocks -- consistent with acute and chronic toxicity, phototoxicity, and other more specialized properties -- would also be useful. Recommendation: Funding agencies, research consortia, and other sponsoring groups should require that research teams use standardized toxicity testing methods, such as those developed by the Chemical Response to Oil Spills Ecological Effects Research Forum (CROSERF)
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