Overview of Aquatic Toxicity Testing under the U.S. EPA Oil Research Program

The National Oil and Hazardous Substances Pollution Contingency Plan (NCP) is the federal government's blueprint for responding to both oil spills and hazardous substance releases (40 CFR 300; www.epa.gov/emergency-response/national-oil-and-hazardous-substances-pollution-contingency-plan-ncp-overview). Subpart J of the NCP establishes a Product Schedule, that includes dispersants and other spill mitigating substances that may be used in carrying out the NCP (40 CFR 300), and also testing requirements and authorization of use procedures for those substances. This research supports EPA's role under the NCP to provide “expertise on human health and ecological effects of oil discharges or releases of hazardous substances, pollutants, or contaminants; ecological and human health risk assessment methods; and environmental pollution control techniques.”

EPA's Office of Research and Development established the Oil Research Program to support the Agency's role in planning and coordinating responses, providing guidance to Regional Response Teams, coordinating a national program of preparedness planning and response, and facilitating research to improve response activities. Currently three phases of research are being focused on specific aspects of the aquatic toxicology of petroleum products and spill mitigating substances. Phase 1 is determining the acute and chronic toxicity of two diluted bitumens (dilbits) from the Alberta Tar Sands region because there is only limited available toxicity data for dilbits, and the spill potential during shipment within the United States. Phase 2 of the research program is evaluating crude oils representing a range of oil physical properties to inform proposed amendments to Subpart J of the U.S. National Contingency Plan. Phase 2 is also evaluating the toxicity of representative dispersants following proposed revisions to the Subpart J regulation. A Phase 3 of the Oil Spills Research Program is planned to evaluate the aquatic toxicity of selected oil spill mitigating substances such as surface washing and bioremediation agents. This paper provides an overview of EPA's oil toxicology research program that will assist the Agency in assessing toxicity of unconventional oils (dilbits), and establish baseline toxicity data for selected crude oils and spill mitigating substances in support of planning and response activities.

Two diluted bitumens (dilbits) from the Alberta Tar Sands region have been selected for acute and chronic toxicity testing with four standard freshwater and marine organisms: Cold Lake Blend (CLB) and Western Canadian Select (WCS). These two dilbits represent a range of the diluted bitumens that are shipped extensively through pipelines in North America. Both fresh and artificially weathered CLB and WCS are being tested. Fresh Alaska North Slope crude oil is also being tested to allow comparison of dilbits to an oil of well-known toxicity. Water accommodated fractions (WAF) of oil were prepared using traditional slow-stir methods (Fig. 1A), and only the aqueous phase is used in toxicity tests. Test solutions are prepared using the variable dilution method (NRC, 2005).

Acute tests will be conducted with early life stages of four aquatic species (Table 1): a fresh water cladoceran zooplankton (Ceriodaphnia dubia) (Fig. 1B), a freshwater fish (fathead minnow, Pimephales promelas) (Fig. 1C), a marine invertebrate (mysid; Americamysis bahia) (Fig. 1D), and a marine fish (inland silverside; Menidia beryllina) (Fig. 1E). Acute and chronic toxicity tests follow U.S. EPA standard effluent testing guidelines for organism age and test methods, modified for use with petroleum mixtures (Table 1; Fig. 2). WAFs are characterized for a range of petroleum hydrocarbons including BTEX (benzene, toluene, ethylbenzene, xylenes), polycyclic aromatic hydrocarbons (PAHs) and their alkyl homologs, normal alkanes (C10–C35), and total petroleum hydrocarbons (TPH). This information will add to the limited available public information on the toxicity data of dilbits (e.g., Dew et al., 2015), and allow more informed hazard assessments in case of dilbit spills in fresh or marine waters of the United States.

EPA is currently evaluating crude oils and testing example dispersants in support of proposed amendments to Subpart J of the NCP. Crude oils representing a range of physical properties are being evaluated in support of switching from Subpart J specified testing with fuel oil #2 to alternative crude oils. Crude oils will be considered that represent a range of physical, chemical and compositional characteristics. Candidate oils to be tested may include light and mid-range crude oils (e.g., Endicott, Dorado) or intermediate fuel oils. EPA is collecting baseline toxicity data with the two aquatic test species currently used for testing under Subpart J. Tests will use the acute methods of Table 1 with the mysid (A. bahia), a marine crustacean invertebrate, and the inland silverside (M. beryllina), a marine fish. Results from this effort are intended to support testing of spill mitigation substances for listing on the Product Schedule, pending any future amendments to the Subpart J regulation.

EPA is also testing four example dispersants that are currently listed on the NCP Product Schedule, as a component of Phase 2 of the Oil Research Program. In addition to the standard acute toxicity tests of dispersants with A. bahia and M. beryllina, chronic toxicity will also be assessed with these two species (Table 2). There is limited information concerning the sublethal toxicity of dispersants currently listed on the Product Schedule. This information would be of value as guidance to responders on possible adverse effects on survival and growth of larval fish and invertebrates caused by longer-term exposure to dispersants such as those that may be encountered during atypical dispersant operations (NRT, 2013). Results of Phase 2 testing will be compared to exiting toxicity results on the Product Schedule and scientific literature. Chronic testing is also being conducted on a third species representative of an additional taxonomic group: the purple sea urchin, Arbacia punctulata, an echinoderm invertebrate (Table 3; Fig. 1F). Testing an additional species was deemed valuable because of the limited information on dispersant toxicity to species other than mysids and silversides, and the potential sensitivity of echinoderms. Dispersants being considered for testing to provide baseline comparative toxicity data include Corexit 9500A, Finasol, Accel, and other products.

Future research plans include evaluating the toxicity of other oil spill mitigating substances such as surface washing and bioremediation agents. Compared to oils and chemical dispersants, there is only very limited information on the toxicity of other types of spill mitigating substances in the scientific literature. The objective of Phase 3 of the EPA Oil Research program will be to evaluate WAF preparation methods and behavior of these other spill mitigating substances under controlled laboratory conditions, and to collect baseline toxicity data using standardized test methods for both freshwater and marine species. Acute toxicity tests with four species (Table 1) are planned with one or two selected agents from each spill mitigation category (e.g., surface washing and bioremediation agents) that are listed on the NCP Product Schedule.

EPA's Office of Research and Development established the Oil Research Program to support the Agency's role in planning and coordinating responses, providing guidance to Regional Response Teams, coordinating a national program of preparedness planning and response, and facilitating research to improve response activities. Traditionally, the Research Program has focused on environmental degradation of oil, and dispersant efficacy. The addition of the toxicity assessment of oils and spill mitigating substances represents a significant research investment, and directly addresses EPA's responsibilities specified in the NCP regarding the ecological effects of oil discharges. The results of the three phases of aquatic toxicity research are anticipated to: (1) substantially add to the body of knowledge on toxicity of both fresh and weathered dilbits; (2) develop baseline toxicity data for new EPA reference oils; (3) determine the chronic toxicity of dispersants and other oil spill mitigation substances using standardized methods, and (4) establish the sea urchin as a third test species, in addition to the Subpart J requirements for testing a crustacean invertebrate (mysid) and fish (inland silverside).

We thank the staff and management of Pegasus Technical Services and Hydrosphere Research for technical and administrative support, and Aaron Redman for review of a draft of this manuscript. This research was supported in part by an appointment to the ORISE participant research program supported by an interagency agreement between the U.S. EPA and the U.S. Department of Energy, and the Oil Spill Liability Trust Fund. The conclusions may not necessarily reflect the views of EPA and no official endorsement should be inferred.