A Comparative Assessment of the Aquatic Toxicity of Corexit 9500 to Marine Organisms.

The use of chemical dispersants during oil spill responses has long been controversial. During the Deepwater Horizon (DWH) oil spill, 1.8 million gallons of dispersant, mainly Corexit 9500, were applied in offshore waters to mitigate the human health and coastal environmental impact of surface oil contamination. To evaluate the potential impact of the dispersant on marine life, 18 species, representing important ecological and commercial taxa, were tested using low-energy, dispersant-only water accommodated fractions (WAFs) of Corexit 9500 and standard acute toxicity test methods. All prepared WAFs were analytically characterized. Analyses included the two dispersant markers found in the dispersant and evaluated in samples collected during the DWH Response, dioctylsulfosuccinate sodium salt, and dipropylene glycol n-butyl ether (DPnB). The median lethal and effective concentrations (LC/EC50s) were calculated using a nominal exposure concentration (mg/L, based on the experimental loading rate of 50 mg/L) and measured DPnB (µg/L). Results ranged from 5.50 to > 50 mg/L dispersant and 492 to > 304,000 µg/L DPnB. Species sensitivity distributions of the data demonstrated that taxa were evenly distributed; however, algae and oysters were among the more sensitive organisms. The calculated 5% hazard concentration (HC5) for DPnB (1172 µg/L) was slightly higher than the USEPA chronic criteria of 1000 µg/L and substantially higher than all measured concentrations of DPnB measured in the Gulf of Mexico during the DWH oil spill response.

MTBE ambient water quality criteria development: a public/private partnership.

A public/private partnership was established in 1997, under the administrative oversight of the American Petroleum Institute (API), to develop aquatic toxicity data sufficient to calculate ambient water quality criteria for methyl tertiary-butyl ether (MTBE), a gasoline oxygenate. The MTBE Water Quality Criteria Work Group consisted of representatives from private companies, trade associations, and USEPA. Funding was provided by the private entities, while aquatic biological/toxicological expertise was provided by industry and USEPA scientists. This public/private partnership constituted a nonadversarial, cost-effective, and efficient process for generating the toxicity data necessary for deriving freshwater and marine ambient water quality criteria. Existing aquatic toxicity data were evaluated for acceptability, consistent with USEPA guidance, and nineteen freshwater and marine tests were conducted by commercial laboratories as part of this effort to satisfy the federal criteria database requirements. Definitive test data were developed and reported under the oversight of industry study monitors and Good Laboratory Practice standards auditors, and with USEPA scientists participating in advisory and critical review roles. Calculated, preliminary freshwater criteria for acute (Criterion Maximum Concentration) and chronic (Criterion Continuous Concentration) exposure effect protection are 151 and 51 mg MTBE/L, respectively. Calculated, preliminary marine criteria for acute and chronic exposure effect protection are 53 and 18 mg MTBE/L, respectively. These criteria values may be used for surface water quality management purposes, and they indicate that ambient MTBE concentrations documented in U. S. surface waters to date do not constitute a risk to aquatic organisms.