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

Abstract

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.

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

“…Thus, the different rates of decrease observed between oil types can likely be explained in part by the different proportions of droplet oil in the WAFs. In addition, the density of our oils increased with increased weathering . As shown by Stokes’ law, the density of the dispersed droplets, along with droplet size, plays an important role in how fast a droplet will rise out of the water column, with less dense droplet oil rising faster than more dense droplet oil.…”

“…However, the bottom 2 panels of Figure demonstrate that as concentrations decrease past a point where the droplet phase starts to become depleted, there is a shift in the dissolved‐phase PAH composition to include higher proportions of the less soluble PAH analytes. Because the PAH compositions of unfiltered HEWAFs and CEWAFs are generally maintained across dilutions and the PAH composition of unfiltered samples resembles the PAH composition of the starting oil , we can expect that the dissolved‐phase PAH composition will start to resemble that of the starting oil (and the unfiltered PAH composition) at very low concentrations. We see evidence for this in the bottom 2 plots of Figure .…”

Photo‐induced toxicity following exposure to crude oil and ultraviolet radiation in 2 Australian fishes

“…Negri et al () reported increased sensitivity of coral larvae that were co‐exposed to UV radiation and crude oil. Studies following the Deepwater Horizon oil spill documented significantly increased toxicity to both pelagic and estuarine fish species after co‐exposure to crude oil and UV radiation (Alloy et al , ; Stieglitz et al ; Sweet et al ); however, the Australian North West Shelf crude oil has a different composition of PAHs than the oil collected following the Deepwater Horizon oil spill (Forth et al , ), and UV radiation in Western Australia is expected to be more intense than in the Gulf of Mexico. Therefore, the aim of the present study was to characterize the photo‐induced toxicity of the Australian North West Shelf oil to black bream embryos and yellowtail kingfish embryos using ambient sunlight during the peak of Australia's summer.…”

Dietary intake of Deepwater Horizon oil-injected live food fish by double-crested cormorants resulted in oxidative stress

“…The preparation and chemical composition of the DWH artificially weathered MC252 oil used in this study are described in Forth et al (2016). Weathering of the oil resulted in the loss of the volatile, lighter weight PAH's, including BTEX compounds.…”