Study Establishes Corexit Analysis Method
– November 21, 2014
Chemists from Oregon State University developed a method that detects and measures the chemical composition of the four Corexit surfactants in seawater.
This research also helped to identify best practices that addresses the complexities of sample collection, handling, and storage for improved toxicity testing and biodegradation experiments. They published their findings in the 2014 Deep-Sea Research II: Topical Studies in Oceanography: Trace analysis of surfactants in Corexit oil dispersant formulations and seawater.
During the Deepwater Horizon oil spill, responders applied an unprecedented amount of dispersant at oil coming from the wellhead and on surface slicks. To assist environmental impact assessments, the Environmental Protection Agency (EPA) obtained the ingredients of four Corexit surfactants commonly known as DOSS, Span 80, Tween 80, and Tween 85. DOSS was the only surfactant that received EPA-determined aquatic life benchmarks for chronic exposure and reporting limits; therefore, it has been the main focus of recent studies to indicate the presence of Corexit. This study’s goals were to develop a sensitive and selective analytical method for quantifying the four surfactant classes in seawater and then use this method to determine the distribution and concentrations of surfactants in the Gulf.
The researchers obtained samples of the individual surfactant components from the Sigma-Aldrich Corporation and the Corexit samples from the University of California, Davis. The seawater samples came from those collected on the R/V Pelican in the vicinity of the blowout site from May 25 to June 6, 2010.
Seawater analysis presents challenges because salt can obstruct and corrode lab equipment. Large-volume injection liquid chromatography (LVI-LC) has been used for testing contaminants in ground and waste water but not for seawater. The team used the LVI-LC and followed it with mass spectrometry. To mitigate the salt problem, they added a wash process during the analysis to divert the salt away from the mass spectrometer prior to compound detection. This method was effective for removing salt from water samples without causing loss of surfactant components.
In the Corexit formulations analyses, DOSS had the highest concentration levels of the four surfactants, followed closely by Tween 80 and then lesser quantities of Tween 85 and Span 80. Compounds resulting from the degradation of DOSS were also present in Corexit. In the seawater samples analyses, lower DOSS concentrations were found at the sea surface with higher concentrations in deeper waters (1,000 meters or more). Detectable levels of DOSS degradation products were also observed in seawater.
Benjamin Place, the study’s lead author, explained that because degradation products of DOSS were found in both seawater and in the original Corexit formulation, “This indicates that they are not unambiguous indicators of DOSS degradation.”
One of the study authors, Jennifer Field, explained the significant progress made in this study, “This remains the only analytical method that has the capability for quantifying all the surfactant classes in Corexit as well as the degradation products of DOSS.” Their on-going research is aimed at documenting the spatial and temporal distributions of DOSS in deep sea sediments.
The team also identified a number of best practices for sampling and sample preservation. They found that field sample preparation significantly impacted the recovery of chemical components from seawater. Immediately freezing water samples reduced or eliminated the loss of chemical components. They also described dilution solutions and storage times and temperatures that maintained sample stability as well as lab procedures that reduced sample contamination.
The study’s authors are Benjamin J. Place, Matt J. Perkins, Ewan Sinclair, Adam L. Barsamian, Paul R. Blakemore, and Jennifer A. Field.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Ecosystem Impacts of Oil and Gas Inputs to the Gulf (ECOGIG) consortium. Other funding sources included the National Science Foundation (OCE-1043224), the National Institute of Environmental Health Sciences (P42ES016465 (Oregon State University Superfund Research Program Award) and T32ES007060), and the Oregon State University N.L. Tartar Research Fellowship.
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