A review of the toxicology of oil in vertebrates: what we have learned following the Deepwater Horizon oil spill.

In the wake of the Deepwater Horizon (DWH) oil spill, a number of government agencies, academic institutions, consultants, and nonprofit organizations conducted lab- and field-based research to understand the toxic effects of the oil. Lab testing was performed with a variety of fish, birds, turtles, and vertebrate cell lines (as well as invertebrates); field biologists conducted observations on fish, birds, turtles, and marine mammals; and epidemiologists carried out observational studies in humans. Eight years after the spill, scientists and resource managers held a workshop to summarize the similarities and differences in the effects of DWH oil on vertebrate taxa and to identify remaining gaps in our understanding of oil toxicity in wildlife and humans, building upon the cross-taxonomic synthesis initiated during the Natural Resource Damage Assessment. Across the studies, consistency was found in the types of toxic response observed in the different organisms. Impairment of stress responses and adrenal gland function, cardiotoxicity, immune system dysfunction, disruption of blood cells and their function, effects on locomotion, and oxidative damage were observed across taxa. This consistency suggests conservation in the mechanisms of action and disease pathogenesis. From a toxicological perspective, a logical progression of impacts was noted: from molecular and cellular effects that manifest as organ dysfunction, to systemic effects that compromise fitness, growth, reproductive potential, and survival. From a clinical perspective, adverse health effects from DWH oil spill exposure formed a suite of signs/symptomatic responses that at the highest doses/concentrations resulted in multi-organ system failure.

Nonlethal Biomarkers of Oxidative Stress in Oiled Sediment Exposed Southern Flounder (Paralichthys lethostigma): Utility for Field-Base Monitoring Exposure and Potential Recovery.

The Deepwater Horizon (DWH) blowout resulted in the deposition of toxic polycyclic aromatic hydrocarbons (PAHs), in the coastal sediments of the Gulf of Mexico. The immediate effects on an ecosystem from an oil spill are clearly recognizable, however the long-term chronic effects and recovery after a spill are still not well understood. Current methodologies for biomonitoring wild populations are invasive and mostly lethal. Here, two potential nonlethal biomonitoring tools for the assessment of PAH toxicity and induced biological alterations in the field, were identified using laboratory-validated methods. In this study, subadult southern flounder (Paralichthys lethostigma) were chronically exposed to DWH surrogate oiled sediments for 35 days; a subset of these exposed flounder were then provided a clean nonexposure period to ascertain the utility of selected biomarkers to monitor recovery post exposure. After chronic exposure, there was an increase in gene expression of cytochrome P450 1A but not glutathione S-transferase. There was also a notable imbalance of oxidants to antioxidants, measured as reduced glutathione, oxidized glutathione, and their ratio in the blood. Evidence of subsequent oxidative damage due to chronic exposure was found through lipid peroxidation and DNA damage assessments of liver, gill, and blood.

Characterization of dissolved and particulate phases of water accommodated fractions used to conduct aquatic toxicity testing in support of the Deepwater Horizon natural resource damage assessment.

In response to the Deepwater Horizon oil spill, the Natural Resource Trustees implemented a toxicity testing program that included 4 different Deepwater Horizon oils that ranged from fresh to weathered, and 3 different oil-in-water preparation methods (including one that used the chemical dispersant Corexit 9500) to prepare a total of 12 chemically unique water accommodated fractions (WAFs). We determined how the different WAF preparation methods, WAF concentrations, and oil types influenced the chemical composition and concentration of polycyclic aromatic hydrocarbons (PAHs) in the dissolved and particulate phases over time periods used in standard toxicity tests. In WAFs prepared with the same starting oil and oil-to-water ratio, the composition and concentration of the dissolved fractions were similar across all preparation methods. However, these similarities diverged when dilutions of the 3 WAF methods were compared. In WAFs containing oil droplets, we found that the dissolved phase was a small fraction of the total PAH concentration for the high-concentration stock WAFs; however, the dissolved phase became the dominant fraction when it was diluted to lower concentrations. Furthermore, decreases in concentration over time were mainly related to surfacing of the larger oil droplets. The initial mean diameters of the droplets were approximately 5 to 10 µm, with a few droplets larger than 30 µm. After 96 h, the mean droplet size decreased to 3 to 5 µm, with generally all droplets larger than 10 µm resurfacing. These data provide a detailed assessment of the concentration and form (dissolved vs particulate) of the PAHs in our WAF exposures, measurements that are important for determining the effects of oil on aquatic species. Environ Toxicol Chem 2017;36:1460-1472. © 2017 SETAC.

Characterization of oil and water accommodated fractions used to conduct aquatic toxicity testing in support of the Deepwater Horizon oil spill natural resource damage assessment.

The Deepwater Horizon blowout resulted in the release of millions of barrels of crude oil. As part of the Trustees' Natural Resource Damage Assessment, a testing program was implemented to evaluate the toxicity of Deepwater Horizon oil and oil/dispersant mixtures to aquatic organisms from the Gulf of Mexico. Because of the variety of exposures that likely occurred, the program included 4 Deepwater Horizon oils, which encompassed a range of weathering states, and 3 different oil-in-water mixing methods, for a total of 12 unique water accommodated fractions (WAFs). The present study reports on the chemical characteristics of these 4 Deepwater Horizon oils and 12 WAFs. In addition, to better understand exposure chemistry, an examination was conducted of the effects of WAF preparation parameters-including mixing energy, starting oil composition, and oil-to-water mixing ratios-on the chemical profiles and final concentrations of these 12 WAFs. The results showed that the more weathered the starting oil, the lower the concentrations of the oil constituents in the WAF, with a shift in composition to the less soluble compounds. In addition, higher mixing energies increased the presence of insoluble oil constituents. Finally, at low to mid oil-to-water mixing ratios, the concentration and composition of the WAFs changed with changing mixing ratios; this change was not observed at higher mixing ratios (i.e., >1 g oil/L). Ultimately, the present study provides a basic characterization of the oils and WAFs used in the testing program, which helps to support interpretation of the more than 500 Deepwater Horizon Natural Resource Damage Assessment toxicity testing results and to enable a comparison of these results with different tests and with the field. Environ Toxicol Chem 2017;36:1450-1459. © 2016 SETAC.

Lack of biological effects of water accommodated fractions of chemically- and physically-dispersed oil on molecular, physiological, and behavioral traits of juvenile snapping turtles following embryonic exposure.

Snapping turtle (Chelydra serpentina) eggs were exposed to two concentrations of chemically- or physically-dispersed water accommodated fractions of weathered Arabian light crude oil (Low=0.5 and High=10 g oil/L water). Solutions were passed through nest substrate to simulate alterations in composition during percolation to egg depth. Hatchlings were raised for 13 months during which numerous endpoints were measured. Prior to percolation, total PAH ("tPAH"; the sum of 52 PAHs measured) in physically-dispersed oil fractions were similar (High, 43; Low 67 mg/L). Following percolation, tPAH was also similar in physically-dispersed fractions (High, 14; Low 24 mg/L). Addition of dispersant increased tPAH prior to percolation in the High treatment (302 mg/L) relative to Low (13 mg/L), but percolation resulted in nearly equal concentrations in both treatments (High, 30; Low, 22 mg/L) due to physical trapping of dispersed oil by the nest substrate. In both chemically- and physically-dispersed fractions, percolation reduced low molecular weight (MW) compounds such that embryos were exposed to primarily mid- to high MW compounds. Total PAH in eggs differed 15-fold between the chemically-dispersed High and physically-dispersed High treatments (560 and 36 microg/kg respectively), the former characterized by higher MW compounds than the latter. While eggs accumulated up to 560 microg/kg tPAH, we observed no effects on hatching success or hatchling/juvenile traits (DNA integrity, survival, growth, metabolism, energy storage, or behavior), our results demonstrate that PAH profiles are altered during percolation, suggesting that experiments with subsurface organisms should be designed to account for compositional changes that occur as the solutions percolate through the substrate.