Chemically Enhanced WAF Research Articles

Comparative toxicity of two diluted bitumens to developing yellow perch (Perca flavescens)

Increasing demand for diluted bitumen (dilbit) has led to the development of the oil sands industry and the expansion of transcontinental pipelines. Dilbit is an unresolved complex mixture with variable diluent and bitumen composition. Thus, it is important to understand the effects of the two most transported dilbits in Canada, Access Western Blend (AWB) and Cold Lake Blend (CLB) on a North America native and freshwater fish species, the yellow perch (Perca flavescens). Fertilized embryos were exposed to both dilbits for 16 days, from <24 h post-fertilization until hatch. The treatment regime was a static daily renewal of water accommodated fractions (WAF) and chemically-enhanced water accommodated fractions (CEWAF) at concentrations ranging from 0.01 to 21.3 μg/L of total polycyclic aromatic compounds (TPACs). Hatched embryos were assessed for malformations and changes in the expression of genes associated with phase I and II detoxification and oxidative stress. The prevalence of developmental malformations increased significantly at the highest concentrations of all treatments, with WAF treatments yielding a higher prevalence than CEWAF. The EC50s for AWB and CLB WAF and CEWAF solutions ranged from 9.8 to 24 μg/L TPACs, with the CEWAF of AWB being the least toxic. Relative mRNA levels of cyp1a showed induction by up to 18-fold in WAF and 50-fold in CEWAF treatments at similar concentrations of measured dilbit in solution. Complementary DNA methylation analysis was assessed and fish embryos exposed to AWB CEWAF and CLB WAF showed decreased DNA methylation profiles with increasing exposure to dilbit, suggesting that global gene expression is increasing in these treatments. With recent approvals of pipelines in North America, these data will support site-specific risk assessments and monitoring of Canadian ecosystems should a pipeline spill occur.

Response of natural phytoplankton communities exposed to crude oil and chemical dispersants during a mesocosm experiment

During the 2010 Deepwater Horizon oil spill, the chemical dispersant Corexit was applied over vast areas of the Gulf of Mexico. Marine phytoplankton play a key role in aggregate formation through the production of extracellular polymeric materials (EPS), an important step in the biological carbon pump. This study examined the impacts of oil and dispersants on the composition and physiology of natural marine phytoplankton communities from the Gulf of Mexico during a 72-hour mesocosm experiment and consequences to carbon export. The communities were treated using the water accommodated fraction (WAF) of oil, which was produced by adding Macondo surrogate oil to natural seawater and mixed for 24 h in the dark. A chemically enhanced WAF (CEWAF) was made in a similar manner, but using a mixture of oil and the dispersant Corexit in a 20:1 ratio as well as a diluted CEWAF (DCEWAF). Phytoplankton communities exposed to WAF showed no significant changes in PSII quantum yield (Fv/Fm) or electron transfer rates (ETRmax) compared to Control communities. In contrast, both Fv/Fm and ETRmax declined rapidly in communities treated with either CEWAF or DCEWAF. Analysis of other photophysiological parameters showed that photosystem II (PSII) antenna size and PSII connectivity factor were not altered by exposure to DCEWAF, suggesting that processes downstream of PSII were affected. The eukaryote community composition in each experimental tank was characterized at the end of the 72 h exposure time using 18S rRNA sequencing. Diatoms dominated the communities in both the control and WAF treatments (52 and 56% relative abundance respectively), while in CEWAF and DCEWAF treatments were dominated by heterotrophic Euglenozoa (51 and 84% respectively). Diatoms made up the largest relative contribution to the autotrophic eukaryote community in all treatments. EPS concentration was four times higher in CEWAF tanks compared to other treatments. Changes in particle size distributions (a proxy for aggregates) over time indicated that a higher degree of particle aggregation occurred in both the CEWAF and DCEWAF treatments than the WAF or Controls. Our results demonstrate that chemically dispersed oil has more negative impacts on photophysiology, phytoplankton community structure and aggregation dynamics than oil alone, with potential implications for export processes that affect the distribution and turnover of carbon and oil in the water column.

Comparison of toxicity effects of fuel oil treated by different dispersants on marine medaka (Oryzias melastigma) embryo

This study aims to evaluate the subacute toxic effects of oil under different treatments on marine organism by simulating natural contaminative processes. In this study, 120# (RMD15) fuel oil was selected as the pollutant and marine medaka (Oryzias melastigma) embryos as the experimental organism. The developmental toxicity of different volume concentrations (0.05%, 0.2%, 1% and 5%) of water-accommodated fractions, biologicallyenhanced water-accommodated fractions, and chemically-enhanced water-accommodated fractions on the embryos in different exposure time (8, 15 and 22 d) were compared and the content of relevant polycyclic aromatic hydrocarbons (PAHs) was studied (in dispersion and in vivo). The subacute toxic effects were assessed in terms of antioxidant activities of enzymes (superoxide dismutase, catalase and glutathione S-transferase) and the blue sac disease (BSD) indexes.The results showed that the BSD indexes of the treatment groups were significantly higher than the respective control groups and showed positive correlations with both concentration and exposure time. The experiments with three antioxidant enzymes indicated that enzymatic activities of the embryos changed dramatically under the oxidation stress of petroleum hydrocarbons, especially after adding the dispersants. With the increase of petroleum hydrocarbon concentration and exposure time, the three enzymes showed different degrees of induction and inhibition effects.

Morphological and molecular effects of two diluted bitumens on developing fathead minnow (Pimephales promelas)

Canada has experienced a significant increase in the transport of diluted bitumen (dilbit), a predominant oil sands product that combines bitumen with diluents derived from oil-gas condensates and other proprietary compounds. The toxicity of dilbit to fish embryos, which are immobile and thus at a high risk of exposure to oil in the event of a spill, remains largely unknown for most species. This study assessed the toxicity of water accommodated fractions (WAF) and chemically enhanced water accommodated fractions (CEWAF) of two winter dilbit blends, Access Western Blend (AWB) and Cold Lake Blend (CLB), to fathead minnow (Pimephales promelas) embryos. The TPH-F EC50s for malformations were 834 and 1058 μg/L for AWB WAF and CEWAF, respectively, and 500 and 715 μg/L for CLB WAF and CEWAF, respectively. Levels of cyp1a mRNA increased up to 46- and 69-fold, respectively, reflecting increasing exposure to polycyclic aromatic compounds (PACs) in AWB and CLB. Similarly, levels of gst mRNA were elevated up to 3.8-fold and 2.7-fold with increasing total concentrations of PACs in AWB and CLB, respectively. However, there were no significant changes in mRNA levels of p53, sod, cat, and gsr. These results suggest that the expression of cyp1a and gst may serve as biomarkers for dilbit exposure in fathead minnow, furthering our understanding of dilbit-responsive indicators of toxicity in fish species native to North America. This study is important as it utilizes the same exposure methodology to examine the toxicity of two commonly used Canadian dilbits, facilitating comparison of dilbit toxicity.

Toxicity of Water-Accommodated Fractions (WAF), Chemically Enhanced WAF (CEWAF) of Oman Crude Oil and Dispersant to Early-Life Stages of Zebrafish (Danio rerio).

This study focused on comparing the lethal and sublethal toxicity of water-accommodated fractions (WAF) and chemically enhanced WAF (CEWAF) of crude oil to zebrafish (Danio rerio) on early life stages (ELS). Results showed that the addition of GM-2 dispersant caused an increase in the levels of total petroleum hydrocarbons (TPHs) and total priority polycyclic aromatic hydrocarbons (ΣPAHs). Based on ΣPAHs, the LC20 estimates for WAF and CEWAF were 4.88 µgL-1 and 1.19µgL-1, respectively, indicating that CEWAF was approximately four times more toxic. CEWAF exposure caused markedly lower hatching rates and higher malformation frequencies than WAF. Meanwhile, the general morphology score (GMS) values in CEWAF were about fourfold lower than that in WAF, indicating that CEWAF exposure induced more significant developmental delay. The results suggested that chemical dispersant enhanced the toxicity of crude oil to zebrafish on ELS and its application could increase the exposure of fishes to crude oil.

Photo-enhanced toxicity of undispersed and dispersed weathered Macondo crude oil to Pacific (Crassostrea gigas) and eastern oyster (Crassostrea virginica) larvae

During the Deepwater Horizon oil spill rapid natural weathering of Macondo crude oil occurred during the transport of oil to coastal areas. In response to the DWH incident, dispersant was applied to Macondo crude oil to reduce the movement of oil to coastal regions. This study aimed to assess the narcotic and phototoxicity of water-accommodated fractions (WAFs) of weathered Macondo crude oil, and chemically-enhanced WAFs of Corexit 9500 to Pacific (Crassostrea gigas) and eastern (Crassostrea virginica) oyster larvae. Phototoxic effects were observed for larval Pacific oysters exposed to combinations of oil and dispersant, but not for oil alone. Phototoxic effects were observed for larval eastern oysters exposed to oil alone and combinations of oil and dispersant. Corexit 9500 did not exhibit phototoxicity but resulted in significant narcotic toxicity for Pacific oysters. Oyster larvae may have experienced reduced survival and/or abnormal development if reproduction coincided with exposures to oil or dispersant.

The sensitivity of a deep-sea fish species (Anoplopoma fimbria) to oil-associated aromatic compounds, dispersant, and Alaskan North Slope crude oil.

A predominant concern following oil spills is toxicity to aquatic organisms. However, few data are available on effects in deep-sea cold water fishes. The present study had 3 major objectives. The first was to investigate the relative sensitivity of the deep-sea species Anoplopoma fimbria (sablefish) to acute effects of 3 aromatic compounds (toluene, 2-methylnaphthalene, and phenanthrene), dispersant alone, and chemically enhanced water accommodated fractions (CEWAFs) of Alaskan North Slope crude oil. The second was to determine the critical target lipid body burden (CTLBB) for sablefish by fitting aromatic hydrocarbon toxicity data to the target lipid model (TLM), which then allowed expression of CEWAF exposures in terms of dissolved oil toxic units. The final aim was to apply a passive sampling method that targets bioavailable, dissolved hydrocarbons as an alternative analytical technique for improved CEWAF exposure assessment. The results indicate that sablefish exhibit sensitivity to Corexit 9500 (96-h median lethal concentration [LC50] = 72.2 mg/L) within the range reported for other fish species. However, the acute CTLBB of 39.4 ± 2.1 μmol/goctanol lies at the lower end of the sensitivity range established for aquatic species. The utility of both toxic units and passive sampling measurements for describing observed toxicity of dispersed oil is discussed. The present study is novel in that a new test species is investigated to address the uncertainty regarding the sensitivity of deep-sea fishes, while also employing modeling and measurements to improve exposure characterization in oil toxicity tests. Environ Toxicol Chem 2018;37:2210-2221. © 2018 SETAC.

Chemically-dispersed crude oil and dispersant affects sperm fertilizing ability, but not sperm swimming behaviour in capelin (Mallotus villosus)

The effects of petroleum aromatic hydrocarbons (PAHs) on the embryonic and larval life stages of teleosts have been extensively examined. However, very little work has been conducted on how spilled oil affects fish sperm and there is no related knowledge concerning oil dispersing agents. The objective of our study was to determine sperm performance of a teleost fish under direct exposure to different concentrations of WAF (water accommodated fraction) and CEWAF (chemically enhanced water accommodated fraction). Capelin sperm motility, swimming behaviour, and sperm fertilization ability were evaluated in a scenario of an oil spill untreated (WAF) and treated (CEWAF) with the dispersant Corexit® EC9500A. Sperm fertilizing ability was lower when exposed to CEWAF concentrations of 16.1 × 103 μg/L total petroleum hydrocarbons and 47.9 μg/L PAH, and when exposed to the dispersant alone. The mechanism responsible for this reduced fertilizing ability is not clear. However, it is not related to the percentage of motile sperm or sperm swimming behaviour, as these were unaffected. WAF did not alter sperm swimming characteristics nor the fertilizing ability. We suggest the dispersant rather than the dispersed oil is responsible for the decrease in the sperm fertilizing ability and hypothesize that the surfactants present in the dispersant affect sperm membrane functionality.

Physiological response of 10 phytoplankton species exposed to macondo oil and the dispersant, Corexit.

Culture experiments were conducted on ten phytoplankton species to examine their biological and physiological responses during exposure to oil and a combination of oil and dispersant. The species tested included a range of taxa typically found in the Gulf of Mexico such as cyanobacteria, chlorophytes, and diatoms. Cultures were exposed to Macondo surrogate oil using the water accommodated fraction (WAF), and dispersed oil using a chemically enhanced WAF (CEWAF) and diluted CEWAF, to replicate conditions following the Deepwater Horizon spill in the Gulf of Mexico. A range of responses were observed, that could broadly class the algae as either "robust" or "sensitive" to oil and/or dispersant exposure. Robust algae were identified as Synechococcus elongatus, Dunaliella tertiolecta, two pennate diatoms Phaeodactylum tricornutum and Navicula sp., and Skeletonema grethae CCMP775, and were largely unaffected by any of the treatments (no changes to growth rate or time spent in lag phase relative to controls). The rest of the phytoplankton, all centric diatoms, exhibited at least some combination of reduced growth rates or increased lag time in response to oil and/or dispersant exposure. Photophysiology did not have a strong treatment effect, with significant inhibition of photosynthetic efficiency (Fv /Fm ) only observed in the CEWAF, if at all. We found that the effects of oil and dispersants on phytoplankton physiology were species-dependent, and not always detrimental. This has significant implications on how oil spills might impact phytoplankton community structure and bloom dynamics in the Gulf of Mexico, which in turn impacts higher trophic levels.

15. The Comparative Toxicity of two Canadian Diluted Bitumens to Developing Yellow Perch (Perca flavescens)

Increasing demand for diluted bitumen (dilbit) has led to the development of the Alberta oil sands industry and the expansion of current and future transcontinental pipelines. However, the growth of oil transportation has led to public concern about the effects of potential dilbit spills to aquatic ecosystems. Although the toxic effects of crude oils through exposure to polycyclic aromatic hydrocarbons (PAH) are well characterized, little is known about the toxic effects of dilbit because of the variable proportions of diluent added to bitumen. Here we assessed the toxicity of the two most transported dilbits in Canada, Access Western Blend (AWB) and Cold Lake Blend (CLB) to developing yellow perch (Perca flavescens), a species distributed throughout North America. Embryos were exposed to dilbit until hatch, or up to 16 days, using a static daily renewal treatment regime of water accommodated fractions (WAF) and chemically-enhanced water accommodated fractions (CEWAF) of dilbit at total PAH (TPAH) concentration ranges of 0.02 to 10.7 μg/L and 0.21 to 20.4 μg/L TPAH, respectively. Results show that with increased TPAH concentration, the frequency of hatched embryos with developmental malformations increased proportionally. Expression of genes associated with phase I and II detoxification, cellular stress, and xenobiotic metabolism were altered in higher TPAH concentrations. This is the first study assessing the toxicity of both AWB and CLB dilbits on wild-sourced fish. With recent approvals of pipelines in North America, these biomarkers will assist risk assessments and monitoring of Canadian ecosystems should a pipeline spill occur.

Corexit, oil and marine microgels

Corexit, an EPA-approved chemical dispersant, was intensively used during the 2010 Deepwater Horizon Oil Spill in the Gulf of Mexico. Current studies surrounding Corexit have mainly focused on its toxicity and oil removal capacity. The potential impact of Corexit on the surface ocean carbon dynamics has remained largely unknown. The spontaneous assembly of DOM (dissolved organic matter) polymers into microgels (POM, particulate organic matter) was demonstrated previously that it can influence various critical processes, such as colloidal pump, microbial loops, and nutrition availability in the surface ocean. Here, we report that Corexit alone can significantly inhibit DOM microgel formation and reduce the stability of pre-existing microgels. However, Corexit and oil, Chemically Enhanced Water Accommodated Fraction (CEWAF), could effectively facilitate DOM microgel formation. The unanticipated disturbance of Corexit and oil spills on the critical DOM-POM continuum warrant particular caution and thus should be considered for future application of Corexit during oil spills.

Exposure to Deepwater Horizon oil and Corexit 9500 at low concentrations induces transcriptional changes and alters immune transcriptional pathways in sheepshead minnows

The 2010 Deepwater Horizon (DWH) oil spill caused the release of 4.9 million barrels of crude oil into the Gulf of Mexico, followed by the application of 2.9 million L of the dispersant, Corexit™ to mitigate the spread of oil. The spill resulted in substantial shoreline oiling, potentially exposing coastal organisms to polyaromatic hydrocarbon (PAH) and dispersant contaminants. To investigate molecular effects in fish following exposure to environmentally relevant concentrations of DWH oil and dispersants, we exposed adult sheepshead minnows (Cyprinodon variegatus) to two concentrations of high-energy water-accommodated fraction (HEWAF), chemically enhanced water-accommodated fraction (CEWAF) or Corexit 9500™ for 7 and 14days. Resulting changes in hepatic gene expression were measured using 8×15K microarrays. Analytical chemistry confirmed PAH concentrations in HEWAF and CEWAF treatments were low (ranging from 0.26 to 5.98μg/L), and likely representative of post-spill environmental concentrations. We observed significant changes to gene expression in all treatments (relative to controls), with Corexit and CEWAF having a greater effect on expression patterns in the liver than HEWAF treatments. Sub-network enrichment analysis of biological pathways revealed that the greatest number of altered pathways in high dose HEWAF and CEWAF treatments occurred following a 7-day exposure. Pathways related to immunity comprised the majority of pathways affected in each treatment, followed by pathways related to blood and circulation processes. Our results indicate that oil composition, concentration, and exposure duration all affect molecular responses in exposed fish, and suggest that low-concentration exposures may result in sub-lethal adverse effects.

Cold Lake Blend diluted bitumen toxicity to the early development of Japanese medaka

Diluted bitumen (dilbit) from Alberta oil sands (Canada) is transported across major continental watersheds, yet little is known about its toxicity to fish if spilled into aquatic environments. The toxicity of Cold Lake (CLB) dilbit was assessed for medaka embryos (Oryzias latipes) exposed to water accommodated fractions (WAF) and chemically-enhanced WAF (CEWAF) using Corexit®EC9500A as dispersant. The effects of CLB toxicity were similar to conventional crude oils and Access Western Blend (AWB) dilbit. The prevalence of malformations and cyp1a mRNA synthesis in hatched fish increased monotonically with concentration during WAF and CEWAF treatments and provided a novel indicator of dilbit PAH toxicity. Apart from nfe2 (an antioxidant transcription factor), there were no statistically significant monotonic exposure-responses of ahr, arnt2, cat, sod, gpx, gst, gsr, g6pdh, p53, and hsp70 transcripts at total polycyclic aromatic hydrocarbons (TPAH) concentrations bracketing EC50s for embryotoxicity (WAF ≅ 3 μg/L; CEWAF ≅ 0.1 μg/L TPAH). Based on measured TPAH concentrations in exposure test solutions, CLB dilbit was 6–10 fold more toxic to medaka than AWB during chronic exposures. Lack of direct monotonic gene transcription responses to increasing oil concentrations during exposures that were embryotoxic suggests that the capacity of the oxidative stress response is limited in earlier lifestages or that differences exist among species in mechanisms of toxicity. This study provides a comparative framework for identifying suitable biomarkers and toxicity methods for those fish species in sensitive lifestages at highest risk of Canadian oil sands dilbit exposure following a spill in the freshwater environment.

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

Comprehensive characterization of exposure media used in toxicology studies is still an area of significant divergence when evaluating potential oil spill impacts. When preparing exposure media used for toxicology testing, small variations in simple parameters such as mixing energy, oil type and loading can significantly affect the concentration of the oil components to which test organisms are exposed. The key goal of this study was compare and contrast the physical and chemical compositions of oil water mixtures prepared using fresh and weathered Macondo-related oils under different conditions of mixing and in the presence/absence of chemical dispersants. All samples were assessed for the presence of droplets, droplet size distribution, and detailed chemical composition including polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbon by fluorescence (TPHF). Preparations were also tested for stability over a 96h period relevant to acute toxicity tests. The results indicate that water accommodated fractions (WAFs) produced consistent, droplet free solutions with concentration that represented the soluble components of the oil used. As expected, chemically-enhanced WAFs (CEWAFs) and high-energy WAFs (HEWAFs) generated large amounts of micron-size droplets and their chemical composition corresponded closely with that of the whole oil. However, the HEWAFs were highly dynamic, and unlike CEWAFs, much of the oil resurfaced within few hours of the initial preparation. Viscosity and lack of dispersability are the limiting factors for preparation of CEWAFs with weathered oils, in contrast HEWAFs did effectively introduce large amounts of weathered oil droplets in the test media. Despite this benefit, droplet sizes significantly decreased in HEWAFs with increase in weathering of the oil creating an additional variable to consider. Because the contribution of small droplets to toxicity is a topic that needs further investigation, the interpretation of results from high-energy preparations needs to be further evaluated. When the TPAHs concentrations of all preparations at all loadings were compared with the publicly available water-column data for samples analyzed during and after the DWH incident response they all ranked above the vast majority of the 10,828 samples reported. Until a better characterization of all the available DWH water column individual-component chemistry data is produced the question of environmental relevance and the pursuit of toxicological studies under more realistic conditions continues to be a significant challenge that should be further explored.

Acute effects of non-weathered and weathered crude oil and dispersant associated with the Deepwater Horizon incident on the development of marine bivalve and echinoderm larvae.

Acute toxicity tests (48-96-h duration) were conducted with larvae of 2 echinoderm species (Strongylocentrotus purpuratus and Dendraster excentricus) and 4 bivalve mollusk species (Crassostrea virginica, Crassostrea gigas, Mytilus galloprovincialis, and Mercenaria mercenaria). Developing larvae were exposed to water-accommodated fractions (WAFs) and chemically enhanced water-accommodated fractions (CEWAFs) of fresh and weathered oils collected from the Gulf of Mexico during the Deepwater Horizon incident. The WAFs (oils alone), CEWAFs (oils plus Corexit 9500A dispersant), and WAFs of Corexit alone were prepared using low-energy mixing. The WAFs of weathered oils had no effect on survival and development of echinoderm and bivalve larvae, whereas WAFs of fresh oils showed adverse effects on larval development. Similar toxicities were observed for weathered oil CEWAFs and WAFs prepared with Corexit alone for oyster (C. gigas and C. virginica) larvae, which were the most sensitive of the tested invertebrate species to Corexit. Mean 10% effective concentration values for total polycyclic aromatic hydrocarbons and dipropylene glycol n-butyl ether (a marker for Corexit) in the present study were higher than all concentrations reported in nearshore field samples collected during and after the Deepwater Horizon incident. The results suggest that water-soluble fractions of weathered oils and Corexit dispersant associated with the Deepwater Horizon incident had limited, if any, acute impacts on nearshore larvae of eastern oysters and clams, as well as other organisms with similar sensitivities to those of test species in the present study; however, exposure to sediments and long-term effects were not evaluated. Environ Toxicol Chem 2016;35:2016-2028. © 2016 SETAC.

Hypoxia depresses CYP1A induction and enhances DNA damage, but has minimal effects on antioxidant responses in sheepshead minnow (Cyprinodon variegatus) larvae exposed to dispersed crude oil

The growing incidence of hypoxic regions in coastal areas receiving high volumes of anthropogenic discharges requires more focused risk assessment of multiple stressors. One area needing further study is the combined effect of hypoxia and oil exposure. This study examined the short-term sublethal effects of co-exposure to hypoxia and water accommodated fractions (WAF) and chemically enhanced WAFs (CEWAFs) of Southern Louisiana Crude oil on detoxification, antioxidant defenses and genotoxicity in early life stage sheepshead minnow (Cyprinodon variegatus). CYP1A induction (evaluated by measuring EROD activity), activity of a number of key antioxidant enzymes (GST, GR, GPx, SOD, CAT, and GCL), levels of antioxidants (tGSH, GSH, and GSSG), evidence of lipid peroxidation (evaluated using the TBARS assay), and DNA damage (evaluated using the comet assay) provided a broad assessment of responses. Contaminant detoxification pathways induced by oil exposure were inhibited by co-exposure to hypoxia, indicating a maladaptive response. The interactive effects of oil and hypoxia on antioxidant defenses were mixed, but generally indicated less pronounced alterations, with significant increases in lipid peroxidation not observed. Hypoxia significantly enhanced DNA damage induced by oil exposure indicating the potential for significant deleterious effects post exposure. This study demonstrates the importance of considering hypoxia as an enhanced risk factor in assessing the effects of contaminants in areas where seasonal hypoxia may be prevalent.

Acute Toxicity of Water-Accommodated Fraction and Chemically Enhanced WAF of Bunker C Oil and Dispersant to a Microalga Tetraselmis tetrathele.

This study assessed the toxicity of water-accommodated fraction (WAF) and chemically enhanced WAF (CEWAF) of bunker C oil and dispersant (DISP) to a microalga, Tetraselmis tetrathele. The 72-h median effective concentration (72-h EC50) of CEWAF and DISP were determined at 3.30% and 2.40%, respectively. The no observed effect concentration (NOEC) of CEWAF to T. tetrathele was at 2.0% and lowest observed effect concentration (LOEC) was at 3.0% while NOEC and LOEC of DISP to T. tetrathele were determined at 1.0% and 2.0%, respectively. The addition of dispersant to oil increased the amount of total PAH present in the CEWAF test solutions. DISP alone was highly toxic, and the toxicity of CEWAF was primarily caused by the presence of dispersant.

Developmental abnormalities and differential expression of genes induced in oil and dispersant exposed Menidia beryllina embryos

Exposure of fish embryos to relatively low concentrations of oil has been implicated in sub-lethal toxicity. The objective of this study was to determine the effects of the exposure of Menidia beryllina embryos at 30–48h post-fertilization to the water accommodated fractions of oil (WAF, 200ppm, v/v), dispersants (20ppm, v/v, Corexit 9500 or 9527), and mixtures of oil and each of the dispersants to produce chemically enhanced water accommodated fractions (CEWAFs) over a 72-hour period. The polyaromatic hydrocarbon (PAH) and benzene, toluene, ethylene and xylene (BTEX) constituents of the 5X concentrated exposure solutions (control, WAF, dispersants and CEWAFs) were determined and those of the 1× exposures were derived using a dilution factor. PAH, BTEX and low molecular weight PAH constituents greater than 1ppb were observed in WAF and the dispersants, but at much higher levels in CEWAFs. The WAF and CEWAFs post-weathering were diluted at 1:5 (200ml WAF/CEWAF: 800ml 25ppt saltwater) for embryo exposures. Mortality, heartbeat, embryo normalcy, abnormality types and severities were recorded. The qPCR assay was used to quantify abundances of transcripts of target genes for sexual differentiation and sex determination (StAR, dmrt-1, amh, cyp19b, vtg and chg-L,), growth regulation (ghr) and stress response (cyp1a and Hsp90); and gapdh served as the housekeeping gene. Temperature was 21±1.5°C throughout the experimental period, while mortality was low and not significantly different (p=0.68) among treatments. Heartbeat was significantly different (0.0034) with the lowest heartbeats recorded in Corexit 9500 (67.5beats/min) and 9527 (67.1beats/min) exposed embryos compared with controls (82.7beats/min). Significantly more treated embryos were in a state of deterioration, with significantly more embryos presenting arrested tissue differentiation compared with controls (p=0.021). Exposure to WAF, dispersants and CEWAF induced aberrant expression of all the genes, with star, dmrt-1, ghr and hsp90 being significantly down-regulated in CEWAF and cyp19b in Corexit 9527. The cyp1a and cyp19b were significantly up-regulated in CEWAFs and WAF, respectively. The molecular endpoints were most sensitive, especially the expression of star, cyp19b, cyp1a, hsp90 and could therefore be used as early indicators of long term effects of Corexit 9500 and 9527 usage in oil spill management on M. beryllina, a valid sentinel for oil pollution events.

Hypoxia Enhances the Toxicity of Corexit EC9500A and Chemically Dispersed Southern Louisiana Sweet Crude Oil (MC-242) to Sheepshead Minnow (Cyprinodon variegatus) Larvae.

Oil exploration and production activities are common in the northern Gulf of Mexico as well as many other coastal and near coastal areas worldwide. Seasonal hypoxia is also a common feature in the Northern Gulf, and many other coastal areas, which is likely to increase in severity and extent with continuing anthropogenic nutrient inputs. Hypoxia has well established physiological effects on many organisms, and it has been shown to enhance the toxicity of polycyclic aromatic hydrocarbons (persistent components of petroleum) in fish. The goal of this study was to examine the combined effects of hypoxia and exposure to contaminants associated with oil spills. We evaluated the effects of short term (48 hr) exposures to Corexit EC9500A, water accommodated fractions (WAF), and chemically enhanced water accommodated fractions (CEWAF) prepared from Southern Louisiana Sweet Crude Oil (MC 242) on survival of sheepshead minnow (Cyprinodon variegatus) larvae held under normoxic (ambient air) or hypoxic (2 mg/L O2) conditions. Results demonstrated that hypoxia significantly enhances mortality observed in response to Corexit or CEWAF solutions. In the latter case, significant interactions between the two stressors were also observed. Our data supports the need to further evaluate the combined stresses imparted by hypoxia and exposure to petroleum hydrocarbons and dispersants.

Toxicity of spill-treating agents and oil to sea urchin embryos

The aim of this study was to assess the joint toxicity of a Maya crude oil and four spill-treating agents (STAs) (CytoSol, Finasol OSR51, Agma OSD569 and OD4000). The acute toxicity of the binary mixtures of the water accommodated fractions (WAFs) obtained independently for the oil and each STA was assessed. The toxicity of the chemically enhanced WAF (CEWAF) of oil and Finasol OSR51 at several dispersant to oil ratios (1:2, 1:10 and 1:100) was also evaluated. The toxicity (EC50) obtained for the WAFs of the STAs was: CytoSol (15.1mL/L)<Agma OSD 569 (9.8mL/L)<OD4000 (2.6mL/L)<and Finasol OSR 51 (1.8mL/L). An accurate description of the toxicity of binary mixtures was obtained by the following models: Concentration Addition (Agma OSD569 and CytoSol), Independent Action (Finasol OSR51) and extended Concentration Addition model to describe antagonistic effects (OD4000). The CEWAFs showed an intermediate position between the more moderate effects of the WAF of oil and the higher toxicity of the WAFs of Finasol OSR51, which suggested the high sensitivity of the sea urchin embryo toward the dispersant.