Characterization and environmental relevance of oil water preparations of fresh and weathered MC-252 Macondo oils used in toxicology testing

Do oil droplets and chemical dispersants contribute to uptake of oil compounds and toxicity of crude oil dispersions in cold-water copepods?

Accidental crude oil spills to the marine environment cause dispersion of oil into the water column through the actions of breaking waves, a process that can be facilitated using chemical dispersants. Oil dispersions contain dispersed micron-sized oil droplets and dissolved oil components, and the toxicity of oil dispersions has been assumed to be associated primarily with the latter. However, most hydrophobic, bioaccumulative and toxic crude oil components are retained within the droplets which may interact with marine filter-feeders. We here summarize the findings of 15 years of research using a unique methodology to generate controlled concentrations and droplet size distributions of dispersed crude oil to study effects on the filter-feeding cold-water copepod Calanus finmarchicus. We focus primarily on the contribution of chemical dispersants and micron-sized oil droplets to uptake and toxicity of oil compounds. Oil dispersion exposures cause PAH uptake and oil droplet accumulation on copepod body surfaces and inside their gastrointestinal tract, and exposures to high exposure (mg/L range) reduce feeding activity, causes reproductive impairments and mortality. These effects were slightly higher in the presence of chemical dispersants, possibly due to higher filtration of chemically dispersed droplets. For C. finmarchicus, dispersions containing oil droplets caused more severe toxic effects than filtered dispersions, thus, oil droplets contribute to the observed toxicity. The methodology for generating crude oil dispersion is a valuable tool to isolate impacts of crude oil microdroplets and can facilitate future research on oil dispersion toxicity and produce data to improve oil spill models.

Limited impact of weathered residues from the Deepwater Horizon oil spill on the gut-microbiome and foraging behavior of sheepshead minnows (Cyprinodon variegatus)

The Deepwater Horizon disaster of April 2010 was the largest oil spill in U.S. history and exerted catastrophic effects on several ecologically important fish species in the Gulf of Mexico (GoM). Within fish, the microbiome plays a key symbiotic role in maintaining host health and aids in acquiring nutrients, supporting immune function, and modulating behavior. The aim of this study was to examine if exposure to weathered oil might produce significant shifts in fish gut-associated microbial communities as determined from taxa and genes known for hydrocarbon degradation, and whether foraging behavior was affected. The gut microbiome (16S rRNA and shotgun metagenomics) of sheepshead minnow (Cyprinodon variegatus) was characterized after fish were exposed to oil in High Energy Water Accommodated Fractions (HEWAF; tPAH = 81.1 ± 12.4 µg/L) for 7 days. A foraging behavioral assay was used to determine feeding efficiency before and after oil exposure. The fish gut microbiome was not significantly altered in alpha or beta diversity. None of the most abundant taxa produced any significant shifts as a result of oil exposure, with only rare taxa showing significant shifts in abundance between treatments. However, several bioindicator taxa known for hydrocarbon degradation were detected in the oil treatment, primarily Sphingomonas and Acinetobacter. Notably, the genus Stenotrophomonas was detected in high abundance in 16S data, which previously was not described as a core member of fish gut microbiomes. Data also demonstrated that behavior was not significantly affected by oil exposure. Potential low bioavailability of the oil may have been a factor in our observation of minor shifts in taxa and no behavioral effects. This study lays a foundation for understanding the microbiome of captive sheepshead minnows and indicates the need for further research to elucidate the responses of the fish gut-microbiome under oil spill conditions.

Recommendations for advancing media preparation methods used to assess aquatic hazards of oils and spill response agents

Laboratory preparation of aqueous test media is a critical step in developing toxicity information needed for oil spill response decision-making. Multiple methods have been used to prepare physically and chemically dispersed oils which influence test outcome, interpretation, and utility for hazard assessment and modeling. This paper aims to review media preparation strategies, highlight advantages and limitations, provide recommendations for improvement, and promote the standardization of methods to better inform assessment and modeling. A benefit of media preparation methods for oil that rely on low to moderate mixing energy coupled with a variable dilution design is that the dissolved oil composition of the water accommodation fraction (WAF) stock is consistent across diluted treatments.  Further, analyses that support exposure confirmation maybe reduced and reflect dissolved oil exposures that are bioavailable and amenable to toxicity modeling.  Variable loading tests provide a range of dissolved oil compositions that require analytical verification at each oil loading. Regardless of test design, a preliminary study is recommended to optimize WAF mixing and settling times to achieve equilibrium between oil and test media. Variable dilution tests involving chemical dispersants (CEWAF) or high energy mixing (HEWAF) can increase dissolved oil exposures in treatment dilutions due to droplet dissolution when compared to WAFs. In contrast, HEWAF/CEWAFs generated using variable oil loadings are expected to provide dissolved oil exposures more comparable to WAFs. Preparation methods that provide droplet oil exposures should be environmentally relevant and informed by oil droplet concentrations, compositions, sizes, and exposure durations characteristic of field spill scenarios. Oil droplet generators and passive dosing techniques offer advantages for delivering controlled constant or dynamic dissolved exposures and larger volumes of test media for toxicity testing. Adoption of proposed guidance for improving media preparation methods will provide greater comparability and utility of toxicity testing in oil spill response and assessment.

Setting the stage to advance oil toxicity testing: Overview of knowledge gaps, and recommendations

The Chemical Response to Oil Spills: Ecological Effects Research Forum created a standardized protocol for comparing the in vivo toxicity of physically dispersed oil to chemically dispersed oil to support science-based decision making on the use of dispersants in the early 2000s. Since then, the protocol has been frequently modified to incorporate advances in technology; enable the study of unconventional and heavier oils; and provide data for use in a more diverse manner to cover the growing needs of the oil spill science community. Unfortunately, for many of these lab-based oil toxicity studies consideration was not given to the influence of modifications to the protocol on media chemistry, resulting toxicity and limitations for the use of resulting data in other contexts (e.g., risk assessments, models). To address these issues, a working group of international oil spill experts from academia, industry, government, and private organizations was convened under the Multi-Partner Research Initiative of Canada's Oceans Protection Plan to review publications using the CROSERF protocol since its inception to support their goal of coming to consensus on the key elements required within a "modernized CROSERF protocol".

Adopting a toxic unit model paradigm in design, analysis and interpretation of oil toxicity testing

The lack of a conceptual understanding and unifying quantitative framework to guide conduct and interpretation of laboratory oil toxicity tests, has led investigators to divergent conclusions that can confuse stakeholders and impede sound decision-making. While a plethora of oil toxicity studies are available and continue to be published, due to differences in experimental design, results between studies often cannot be compared. Furthermore, much resulting data fails to advance quantitative effect models that are critically needed for oil spill risk and impact assessments. This paper discusses the challenges posed when evaluating oil toxicity test data based on traditional, total concentration-based exposure metrics and offers solutions for improving the state of practice by adopting a unifying toxic unit (TU) model framework. Key advantages of a TU framework is that differences in test oil composition, sensitivity of the test organism/endpoint, and toxicity test design (i.e., type of test) can be taken into quantitative account in predicting aquatic toxicity. This paradigm shift is intended to bridge the utility of laboratory oil toxicity tests with improved assessment of effects in the field. To illustrate these advantages, results from literature studies are reassessed and contrasted with conclusions obtained based on past practice. Using instructive examples, model results are presented to explain how dissolved oil composition and concentrations and resulting TUs vary in WAFs prepared using variable loading or dilution test designs and the important role that unmeasured oil components contribute to predicted oil toxicity. Model results are used to highlight how the TU framework can serve as a valuable aid in designing and interpreting empirical toxicity tests and provide the data required to validate/refine predictive toxicity models. To further promote consistent exposure and hazard assessment of physically and chemically dispersed oil toxicity tests recommendations for advancing the TU framework are presented.

Impaired grazing of marine protozoa in sub-lethal exposure to the water accommodated fraction of crude oil and dispersant

Despite the advances in safety technology and the improved implementation of precautionary measures, crude oil pollution has been occurring in the oceans globally. The water accommodated fraction (WAF) of crude oil and chemical dispersant are hypothesized to cause sub-lethal adverse effects on marine protists that are pivotal consumers of primary production. Exposure experiments were conducted to investigate the effects of crude oil and dispersant pollutants on the growth and grazing, separately, of protozoa species in cultures. In exposure to 0-30 μL L^-1 of chemically enhanced WAF (CEWAF), the heterotrophic dinoflagellate Protoperidinium sp. and the ciliate Metacylis sp. showed slower positive population growth or negative population growth even at low concentrations. The dose-response model showed that Protoperidinium sp. and Metacylis sp. were highly susceptible to the CEWAF toxicity (median inhibition concentrations (IC₅₀) at 1.1 and 5.9 μL L^-1, respectively) while one algal species Ditylum brightwellii was relatively tolerant to the toxicity (IC₅₀ at 168.7 μL L^-1). With suppressed growth and impaired grazing of the protozoan species at high CEWAF concentrations, accumulation of their algal prey in culture containers was observed, as reflected by higher final:initial prey ratios at high CEWAF concentrations. Additionally, exposure experiments to the treatments of WAF, dispersant alone (Disp), and CEWAF of the same concentration revealed that the heterotrophic dinoflagellate Oxyrrhis marina had reduced bulk grazing impact towards its algal prey population in all three treatments when compared to the control treatment (i.e., grazing mortality of prey at 1.05 d^-1). Similarly, Protoperidinium sp. and Metacylis sp. had reduced per capita prey ingestion rates in exposure to WAF and CEWAF when compared to the control treatments. This study provides experimental evidence for the potential link between impaired grazing activities and the formation of algal blooms in sub-lethal exposure to crude oil pollutants.

Exposure methodologies for dissolved individual hydrocarbons, dissolved oil, water oil dispersions, water accommodated fraction and chemically enhanced water accommodated fraction of fresh and weathered oil

Characterizing the nature and effects of oil released into the marine environment is very challenging. It is generally recognized that "environmentally relevant" conditions for exposure involve a range of temporal and spatial conditions, a range of exposure pathways (e.g., dissolved, emulsions, sorbed onto particulates matter), and a multitude of organisms, populations, and ecosystems. Various exposure methodologies have been used to study the effects of oil on aquatic organisms, and uniform protocols and exposure methods have been developed for the purposes of regulatory toxicological assessments. Ultimately, all exposure methods have drawbacks, it is impossible to totally mimic field conditions, and the choice of exposure methodology depends on the specific regulatory, toxicological, or other research questions to be addressed. The aim of this paper is to provide a concise review of the state of knowledge to identify gaps in that knowledge and summarize challenges for the future.

Application of chemical herders do not increase acute crude oil toxicity to cold-water marine species

Chemical herders may be used to sequester and thicken surface oil slicks to increase the time window for performing in situ burning of spilled oil on the sea surface. For herder use to be an environmentally safe oil spill response option, information regarding their potential ecotoxicity both alone and in combination with oil is needed. This study aimed at assessing if using herders can cause toxicity to cold-water marine organisms. Our objective was to test the two chemical herders Siltech OP-40 (OP-40) and ThickSlick-6535 (TS-6535) with and without oil for toxicity using sensitive life stages of cold-water marine copepod (Calanus finmarchicus) and fish (Gadus morhua). For herders alone, OP-40 was consistently more toxic than TS-6535. To test herders in combination with oil, low-energy water accommodated fractions (LE-WAFs, without vortex) with Alaskan North Slope crude oils were prepared with and without herders. Dissolution of oil components from surface oil was somewhat delayed following herder application, due to herder-induced reduction in contact area between water and oil. The LE-WAFs were also used for toxicity testing, and we observed no significant differences in toxicity thresholds between treatments to LE-WAFs generated with oil alone and oil treated with herders. The operational herder-to-oil ratio is very low (1:500), and the herders tested in the present work displayed acute toxicity at concentrations well above what would be expected following in situ application. Application of chemical herders to oil slicks is not expected to add significant effects to that of the oil for cold-water marine species exposed to herder-treated oil slicks.

Marine Algal Sensitivity to Source and Weathered Oils

After the Deepwater Horizon oil spill in 2010, toxicity tests were conducted using 4 microalgae (Dunaliella tertiolecta, Skeletonema costatum, Isochrysis galbana, and Thalassiosira pseudonana) and one macroalga (Ectocarpus siliculosus) to study potential impacts on phytoplankton and other primary producers in the Gulf of Mexico and characterize species sensitivity. Tests were performed with Corexit 9500 and fresh source oil and weathered oil samples collected from the field during the Deepwater Horizon oil spill. Because crude oils are mixtures of poorly water-soluble hydrocarbons, dosing was performed using water-accommodated fractions (WAFs) and chemically enhanced (CE) WAFs with the addition of dispersant at a 1:20 dispersant:oil ratio using standard toxicity testing protocols. Exposure media were analyzed for volatile organic compounds, parent and alkylated polycyclic aromatic hydrocarbons, and saturated hydrocarbon compounds. Toxicity was reported as no-observable effect concentration and median effect concentration (EC50) values for average specific growth rate based on nominal percent dilution of stock solution WAFs and sum of dissolved oil toxic units for WAF/CEWAF tests. The macroalga and green alga D. tertiolecta were largely unaffected by any WAF or CEWAFs tested. Isochrysis galbana was found to be the most sensitive species overall with significant growth rate inhibitions for dispersant and all the WAFs/CEWAFs tested. Physically dispersed source oils were generally more toxic than weathered oils. The protectiveness of the chronic toxic units was effective at identifying observed algal growth rate inhibitions across algal species and oil types despite the impact of dispersants.  Environ Toxicol Chem 2021;40:2742-2754. © 2021 SETAC.

Toxicity assessment of a novel oil dispersant based on silica nanoparticles using Fathead minnow

Oil spill accidents are a major concern for aquatic organisms. In recent history, the Deepwater Horizon blowout spilled 500 million liters of crude oil into the Gulf of Mexico. Corexit 9500A was used to disperse the oil since it was the method approved at that time, despite safety concerns about its use. A better solution is necessary for dispersing oil from spills that reduces the toxicity to exposed aquatic organisms. To address this challenge, novel engineered nanoparticles were designed using silica cores grafted with hyperbranched poly(glycidol) branches. Because the silica core and polymers are known to be biocompatible, we hypothesized that these particles are nontoxic to fathead minnows (Pimephales promelas) and would decrease their exposure to oil polyaromatic hydrocarbons. Fathead minnow embryos, juveniles and adult stages were exposed to the particles alone or in combination with a water-accommodated fraction of oil. Acute toxicity of nanoparticles to fish was tested by measuring mortality. Sub-lethal effects were also measured including gene expression of cytochrome P450 1a (cyp1a) mRNA and heart rate in embryos. In addition, a mixture of particles plus the water-accommodated fraction was directly introduced to adult female fathead minnows by gavage. Three different nanoparticle concentrations were used (2, 10, and 50 mg/L) in either artificial fresh water or the water-accommodated fraction of the oil. In addition, nanoparticle-free controls were carried out in the two solutions. No significant mortality was observed for any age group or nanoparticle concentration, suggesting the safety of the nanoparticles. In the presence of the water-accommodated fraction alone, juvenile and adult fathead minnows responded by increasing expression of cyp1a. The addition of nanoparticles to the water-accommodated fraction reduced cyp1a gene expression in treatments. Heart rate was also restored to normal parameters in embryos co-exposed to nanoparticles and to the water-accommodated fraction. Measurement of polyaromatic hydrocarbons confirmed their presence in the tested solutions and the reduction of available PAH in WAF treated with the nanoparticles. Our findings suggest the engineered nanoparticles may be protecting the fish by sequestering polyaromatic hydrocarbons from oil, measured indirectly by the induction of cypa1 mRNAs. Furthermore, chemical analysis showed a reduction in PAH content in the water accommodated fraction with the presence of nanoparticles.

Hypoxia and reduced salinity exacerbate the effects of oil exposure on sheepshead minnow (Cyprinodon variegatus) reproduction

Estuaries of the northern Gulf of Mexico are dynamic environments, with fluctuations in salinity and dissolved oxygen, including areas of seasonal hypoxia. Fish that reside and reproduce in these estuaries, including sheepshead minnow (Cyprinodon variegatus; SHM), were at significant risk of oil exposure following the Deepwater Horizon oil spill. It is poorly understood how differences in environmental conditions during oil exposure impact its toxicity. The present study investigated the effects of crude oil high-energy water accommodated fraction (HEWAF) on SHM reproduction in three environmental scenarios (normoxic, hypoxic, and hypoxic with low salinity) to determine if differences in salinity (brackish vs low salinity) and dissolved oxygen (normoxia vs hypoxia) could exacerbate the effects of HEWAF-derived polycyclic aromatic hydrocarbons (PAHs). We observed that HEWAF exposure significantly increased liver somatic index of SHM compared to control, but this effect was not exacerbated by hypoxia or low salinity. HEWAF exposure also significantly decreased egg production and egg fertilization rate, but only in the hypoxic and hypoxic with low salinity scenarios. A significant correlation existed between body burdens of PAHs and reproductive endpoints, providing substantial evidence that oil exposure reduced reproductive capacity in SHM, across a range of environmental conditions. These data suggest that oil spill risk assessments that fail to consider other environmental stressors (i.e. hypoxia and salinity) may be underestimating risk.

Transgenerational effects of polycyclic aromatic hydrocarbon exposure on sheepshead minnows (Cyprinodon variegatus)

The Deepwater Horizon oil spill resulted in the release of over 640 million L of crude oil into the Gulf of Mexico, affecting over 2000 km of shoreline, including estuaries that serve as important habitats and nurseries for aquatic species. Cyprinodon variegatus (sheepshead minnow) are small-bodied fish that inhabit northern Gulf of Mexico estuaries, are easily adaptable to laboratory conditions, and are commonly used in toxicological assessment studies. The purpose of the present study was to determine the somatic, reproductive, and developmental effects of an environmentally relevant polycyclic aromatic hydrocarbon (PAH) mixture, the oil high-energy water accommodated fraction (HEWAF), on experimentally exposed sheepshead minnow (F₀ ) as well as 2 generations of offspring (F₁ and F₂ ) without additional exposure. The F₀ generation exposed to HEWAF had increased liver somatic indices, altered egg production, and decreased fertilization. Several developmental endpoints in the F₁ were altered by F₀ HEWAF exposure. As adults, low HEWAF-exposed F₁ females demonstrated decreased weight and length. Both the F₁ and F₂ generations derived from high HEWAF-exposed F₀ had deficits in prey capture compared to control F₁ and F₂ , respectively. Correlations between endpoints and tissue PAHs provide evidence that the physiological effects observed were associated with hydrocarbon exposure. These data demonstrate that PAHs were capable of causing physiological changes in exposed adult sheepshead minnow and transgenerational effects in unexposed offspring, both of which could have population-level consequences. Environ Toxicol Chem 2019;38:638-649. © 2018 SETAC.

Interactions between Crassostrea virginica larvae and Deepwater Horizon oil: Toxic effects via dietary exposure

The Deepwater Horizon (DWH) disaster released crude oil in the Gulf of Mexico for 87 days, overlapping with the reproductive season and recruitment of the oyster Crassostrea virginica. The pelagic larval life stages of C. virginica are particularly vulnerable to contaminants such as polycyclic aromatic hydrocarbons (PAHs) and oil droplets. Based on their lipophilic properties, PAHs and oil droplets can adsorb onto phytoplankton and filter-feeding C. virginica larvae may be exposed to these contaminants bound to suspended sediment, adsorbed onto algal and other particles, or in solution. This study examined the effects of exposure of C. virginica larvae to algae mixed with DWH oil. In a 14-day laboratory exposure, 5 day-old C. virginica larvae were exposed to Tisochrysis lutea mixed with four concentrations of unfiltered DWH oil (HEWAF) in a static renewal system. Larval growth, feeding capacity, abnormality and mortality were monitored throughout the exposure. Total PAH (n = 50) content of the water medium, in which larvae were grown, were quantified by GC/MS-SIM. Oil droplets were observed bound to algae, resulting in particles in the size-range of food ingested by oyster larvae (1-30 μm). After 14 days of exposure, larval growth and survival were negatively affected at concentrations of tPAH50 as low as 1.6 μg L^-1. GC/MS-SIM analysis of the exposure medium confirmed that certain PAHs were also adsorbed by T. lutea and taken up by oyster larvae via ingestion of oil droplets and/or contaminated algae. Long-term exposure to chronic levels of PAH (1.6-78 μg tPAH50 L^-1) was shown to negatively affect larval survival. This study demonstrates that dietary exposure of oyster larvae to DWH oil is a realistic route of crude oil toxicity and may have serious implications on the planktonic community and the food chain.

Oil toxicity test methods must be improved

A review of the literature on oil toxicity tests showed a high diversity of reported test methods that may affect the composition, stability, and toxicity of oil solutions. Concentrations of oil in test solutions are dynamic because hydrocarbons evaporate, partition to test containers, bioaccumulate, biodegrade, and photo-oxidize. As a result, the composition and toxicity of test solutions may vary widely and create significant obstacles to comparing toxicity among studies and to applying existing data to new risk assessments. Some differences in toxicity can be resolved if benchmarks are based on measured concentrations of hydrocarbons in test solutions, highlighting the key role of chemical analyses. However, analyses have often been too infrequent to characterize rapid and profound changes in oil concentrations and composition during tests. The lack of practical methods to discriminate particulate from dissolved oil may also contribute to underestimating toxicity. Overall, current test protocols create uncertainty in toxicity benchmarks, with a high risk of errors in measured toxicity. Standard oil toxicity tests conducted in parallel with tests under site-specific conditions would provide an understanding of how test methods and conditions affect measured oil toxicity. Development of standard test methods could be achieved by collaborations among university, industry, and government scientists to define methods acceptable to all 3 sectors. Environ Toxicol Chem 2019;38:302-311. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Inter-laboratory calibration of estimated oil equivalent (EOE) concentrations of a water accommodated fraction (WAF) of oil and a chemically enhanced WAF (CEWAF)

Chemical characterization of the presence of oil in environmental samples are performed using methods of varying complexity. Extraction of samples with an organic solvent and analysis by fluorescence spectrometry has been shown to be a rapid and effective screening technique for petroleum in the environment. During experiments, rapid analysis of oil by fluorescence provides the opportunity for researchers to modify the experimental conditions in real time. Estimated Oil Equivalents (EOE) relies on the fluorescence measurement of the aromatic compounds to estimate the oil concentration.

The present intercalibration study was designed to investigate whether different fluorometer instruments can reliably measure EOE and whether the results are intercomparable. Additionally, the need for extraction of oil compounds into an organic solvent was investigated. Three different fluorometers were used in three different laboratories: a Horiba Aqualog, a Turner Trilogy and a Shimadzu Spectrofluorophotometer RF-1501. Results from these different instruments showed excellent agreement for EOE determinations. A very high correlation was found between the EOE results obtained with Aqualog Horiba and Turner Trilogy (r² = 0.9999), with no significant differences between the mean EOE results (t-test, p = 0.30), and the Aqualog Horiba and Shimadzu (r² = 0.995) fluorometers, with no statistically difference between the EOE results obtained by the two instruments (p = 0.40).

Field-collected crude oil, weathered oil and dispersants differentially affect the early life stages of freshwater and saltwater fishes

The Deepwater Horizon (DWH) oil spill was the biggest in US history and released 3.19 million barrels of light crude oil into the Gulf of Mexico. In this study, we compared the toxicity of water accommodated fractions (WAFs) of naturally weathered crude oils, source oil, and source oil with dispersant mixtures and their effects on developing sheepshead minnow and zebrafish. Although a freshwater fish, zebrafish has been used as a model for marine oil spills owing to the molecular and genetic tools available and their amenability to lab care. Our study not only aimed to determine the effect of crude oil on early life stages of these two fish species, but also aimed to determine whether dissolved crude oil constituents were similar in fresh and saltwater, and if freshwater fish might be a suitable model to study marine spills. Weathering and dispersant had similar effects on WAF composition in both fresh and saltwater, except that the saltwater source oil + dispersant WAF had markedly higher PAH levels than the freshwater equivalent. WAF exposure differentially affected survival, as the LC50 values in %WAF for the zebrafish and sheepshead minnow exposures were 44.9% WAF (95% confidence interval (C.I.) 42.1-47.9) and 16.8% WAF (95% C.I. 13.7-20.5); respectively. Exposure increased heart rate of zebrafish embryos, whereas in sheepshead, source oil exposure had the opposite effect. WAF exposure altered mRNA expression of biotransformation makers, vitellogenin and neurodevelopment genes in both species. Muscle deformations were only found in oil-exposed zebrafish. This is one of the most comprehensive studies to date on crude oil toxicity, and highlights the species-specific differences in cardiotoxicity, estrogenic effects, biotransformation enzyme induction and potential neurotoxicity of crude oil exposure.

Crude oil cardiotoxicity to red drum embryos is independent of oil dispersion energy

The potential bioavailability of toxic chemicals from oil spills to water column organisms such as fish embryos may be influenced by physical dispersion along an energy gradient. For example, a surface slick with minimal wave action (low energy) could potentially produce different toxic effects from high energy situations such as pressurized discharge from a blown wellhead. Here we directly compared the toxicity of water accommodated fractions (WAFs) of oil prepared with low and high mixing energy (LEWAFs and HEWAFs, respectively) using surface oil samples collected during the 2010 Deepwater Horizon spill, and embryos of a representative nearshore species, red drum (Sciaenops ocellatus). Biological effects of each WAF type was quantified with several functional and morphological indices of developmental cardiotoxicity, providing additional insight into species-specific responses to oil exposure. Although the two WAF preparations yielded different profiles of polycyclic aromatic hydrocarbons (PAHs), cardiotoxic phenotypes were essentially identical. Based on benchmark thresholds for both morphological and functional cardiotoxicity, in general LEWAFs had lower thresholds for these phenotypes than HEWAFs based on total PAH measures. However, HEWAF and LEWAF toxicity thresholds were more similar when calculated based on estimates of dissolved PAHs only. Differences in thresholds were attributable to the weathering state of the oil samples.

Passive dosing yields dissolved aqueous exposures of crude oil comparable to the CROSERF (Chemical Response to Oil Spill: Ecological Effects Research Forum) water accommodated fraction method

The Chemical Response to Oil Spill: Ecological Effects Research Forum's water accommodated fraction procedure was compared with 2 alternative techniques in which crude oil was passively dosed from silicone tubing or O-rings. Fresh Macondo oil (MC252) was dosed at 30 mg/L using each approach to investigate oil dissolution kinetics, which was monitored by fluorometry as estimated oil equivalents (EOEs). Subsequent experiments with each dosing method were then conducted at multiple oil loadings. Following equilibration, test media were analytically characterized for polyaromatic hydrocarbons (PAHs) using gas chromatography (GC)-mass spectrometry and dissolved oil using biomimetic solid-phase microextraction (SPME). The results showed that equilibrium was achieved within 72 h for all methods. Measured PAH concentrations were compared with oil solubility model predictions of dissolved exposures. The concentration and composition of measured and predicted dissolved PAHs varied with oil loading and were consistent between dosing methods. Two-dimensional GC compositional data for this oil were then used to calculate dissolved toxic units for predicting MC252 oil acute toxicity across the expected range of species sensitivities. Predicted toxic units were nonlinear with loading and correlated to both EOE and biomimetic SPME. Passive dosing methods provide a practical strategy to deliver and maintain dissolved oil concentrations while avoiding the complicating role that droplets can introduce in exposure characterization and test interpretation. Environ Toxicol Chem 2018;37:2810-2819. © 2018 SETAC.

Comparative toxicity of Corexit® 9500, oil, and a Corexit®/oil mixture on the eastern oyster, Crassostrea virginica (Gmelin)

Given their particle feeding behavior, sessile nature, and abundance in coastal zones, bivalves are at significant risk for exposure to oil and oil dispersant following environmental disasters like the Deepwater Horizon oil spill. However, the effects of oil combined with oil dispersants on the health of oysters are not well studied. Therefore, eastern oysters (Crassostrea virginica) were exposed in vivo to Corexit^® 9500, crude oil (high-energy water accommodated fraction; HEWAF), and a Corexit^®/oil mixture (chemically-enhanced water accommodated fraction; CEWAF) to evaluate potential toxic effects on immunological (phagocytosis and respiratory burst), physiological (feeding rate), and histological endpoints. Phagocytosis was significantly increased following CEWAF exposure only. Respiratory burst was significantly decreased following Corexit^® exposure, but significantly increased following exposure to the highest concentration of CEWAF. Oyster feeding rates were significantly decreased following exposure to Corexit^®, HEWAF, and CEWAF, and were most sensitive to CEWAF exposure. These modulations of important immunological and physiological functions could result in serious health outcomes for oysters, such as increased parasitism and decreased growth. Our experiments showed that subtle, sub-lethal effects occurred following acute in vivo exposure to Corexit^®, HEWAF, and CEWAF, though oysters were not equally sensitive to the three components. Data from this study can be used for more accurate risk assessment concerning the impact of oil and Corexit^® on the health of oysters.

Diagnostic tool to ascertain marine phytoplankton exposure to chemically enhanced water accommodated fraction of oil using Fourier Transform Infrared spectroscopy

Phytoplankton alter their macromolecule composition in response to changing environmental conditions. Often these changes are consistent and can be used as indicators to predict their exposure to a given condition. FTIR-spectroscopy is a powerful tool that provides rapid snapshot of microbial samples. We used FTIR to develop signature macromolecular composition profiles of three cultures: Skeletonema costatum, Emiliania huxleyi, and Navicula sp., exposed to chemically enhanced water accommodated oil fraction (CEWAF) in artificial seawater and control. Using a multivariate model created with a Partial Least Square Discriminant Analysis of the FTIR-spectra, classification of CEWAF exposed versus control samples was possible. This model was validated using aggregate samples from a mesocosm study. Analysis of spectra and PCA-loadings plot showed changes to carbohydrates and proteins in response to CEWAF. Overall we developed a robust multivariate model that can be used to identify if a phytoplankton sample has been exposed to oil with dispersant.

Maternal polycyclic aromatic hydrocarbon (PAH) transfer and effects on offspring of copepods exposed to dispersed oil with and without oil droplets

Copepods of the genus Calanus have the potential for accumulating lipophilic oil components due to their high lipid content and found to filter and ingest oil droplets during exposure. As female copepods produce eggs at the expense of lipid storage, there is a concern for transfer of lipophilic contaminants to offspring. To assess the potential for maternal transfer of oil components, ovigerous female copepods (Calanus finmarchicus) were exposed to filtered and unfiltered oil dispersions for 4 days, collected and eggs maintained in clean seawater and hatching and gene expression examined in hatched nauplii. Oil droplet exposure contributed to polycyclic aromatic hydrocarbon (PAH) uptake in dispersion-treated adult copepods, as displayed through PAH body residue analyses and fluorescence microscopy. Applying the latter methodology, transfer of heavy PAH from copepod mothers to offspring were detected Subtle effects were observed in offspring as evidenced by a temporal reduction in hatching success appear to be occurring only when mothers were exposed to the unfiltered oil dispersions. Offspring reared in clean water through to late naupliar stages were collected for RNA extraction and preparation of libraries for high-throughput transcriptome sequencing. Differentially expressed genes were identified through pairwise comparisons between treatments. Among these, several expressed genes have known roles in responses to chemical stress including xenobiotic metabolism enzymes, antioxidants, chaperones, and components of the inflammatory response. While gene expression results suggest a transgenerational activation of stress responses, the increase in relatively small number of differentially expressed genes suggests a minor long-term effect on offspring following maternal exposure.

Analysis of Photoirradiated Water Accommodated Fractions of Crude Oils Using Tandem TIMS and FT-ICR MS

For the first time, trapped ion mobility spectrometry (TIMS) in tandem with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is applied to the analysis of the low energy water accommodated fraction (WAF) of a crude oil as a function of the exposure to light. The TIMS-FT-ICR MS analysis provided, in addition to the heteroatom series identification, new insights into the WAF isomeric complexity (e.g., [m/z; chemical formula; collision cross section] data sets) for a better evaluation of the degree of chemical and structural photoinduced transformations. Inspection of the [m/z; chemical formula; collision cross section] data sets shows that the WAF composition changes as a function of the exposure to light in the first 115 h by initial photosolubilization of HC components and their photo-oxidation up to O_4-5 of mainly high double bond equivalence species (DBE > 9). The addition of high resolution TIMS (resolving power of 90-220) to ultrahigh resolution FT-ICR MS (resolving power over 400k) permitted the identification of a larger number of molecular components in a single analysis (e.g., over 47k using TIMS-MS compared to 12k by MS alone), with instances of over 6-fold increase in the number of molecular features per nominal mass due to the WAF isomeric complexity. This work represents a stepping stone toward a better understanding of the WAF components and highlights the need for better experimental and theoretical approaches to characterize the WAF structural diversity.

Sensitivity of eastern oyster (Crassostrea virginica) spermatozoa and oocytes to dispersed oil: Cellular responses and impacts on fertilization and embryogenesis

The 2010 Deepwater Horizon (DWH) oil spill released millions of barrels of oil and dispersant into the Gulf of Mexico. The timing of the spill coincided with the spawning season of Crassostrea virginica. Consequently, gametes released in the water were likely exposed to oil and dispersant. This study aimed to (i) evaluate the cellular effects of acute exposure of spermatozoa and oocytes to surface slick oil, dispersed mechanically (HEWAF) and chemically (CEWAF), using flow-cytometric (FCM) analyses, and (ii) determine whether the observed cellular effects relate to impairments of fertilization and embryogenesis of gametes exposed to the same concentrations of CEWAF and HEWAF. Following a 30-min exposure, the number of spermatozoa and their viability were reduced due to a physical action of oil droplets (HEWAF) and a toxic action of CEWAF respectively. Additionally, reactive oxygen species (ROS) production in exposed oocytes tended to increase with increasing oil concentrations suggesting that exposure to dispersed oil resulted in an oxidative stress. The decrease in fertilization success (1-h), larval survival (24-h) and increase in abnormalities (6-h and 24-h) may be partly related to altered cellular characteristics. FCM assays are a good predictor of sublethal effects especially on fertilization success. These data suggest that oil/dispersant are cytotoxic to gametes, which may affect negatively the reproduction success and early development of oysters.