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Research Document 2017/064

Review of Methods for Measuring the Toxicity to Aquatic Organisms of the Water Accommodated Fraction (WAF) and Chemically-Enhanced Water Accommodated Fraction (CEWAF) of petroleum

By Adams, J., Charbonneau, K., Tuori, D., Brown, R.S. and Hodson, P.V.


The shipment of diluted bitumen (dilbit) to Canadian refineries and ports is increasing with the expansion of its production in northern Alberta. Dilbit has unique physical and chemical properties relative to conventional crude oils, including rapid weathering and greater adhesion and viscosity that affect its fate, behaviour and effects in marine and freshwater ecosystems. These properties may also interact with commonly used toxicity test protocols to affect measurements of toxicity and change the outcome of ecological risk assessments of dilbit spills. The objectives of this report were: to survey existing methods for oil toxicity tests to identify strengths and weaknesses that could inform the development of standardized methods for testing dilbit; to identify and analyze the advantages and disadvantages of various test methods, recognizing diversity in their objectives; to develop a proposed framework for oil toxicity test methods that links oil type, test species and relevant aquatic environment to the goals of toxicity testing, as a basis for selecting specific test protocols; and to identify relevant research needs.

The Chemical Response to Oil Spills: Ecological Effects Research Forum (CROSERF) recommended standard protocols to prepare Water Accommodated Fractions (WAFs) and Chemically-Enhanced Water Accommodated Fractions (CEWAFs) of crude oil for toxicity tests. The intent was to improve the comparability of toxicity data among studies and their application to Ecological Risk Assessments (ERAs) of oil spills. This survey of peer-reviewed reports of oil toxicity tests with fish catalogued the array of methods actually used. Most reports were published since 2000, and each was assessed to determine if the methods followed CROSERF protocols, provided sufficient information to understand the test results and to support ERAs, and overall, whether there are problems inherent in current practice. CROSERF protocols were also analyzed to determine their suitability for toxicity tests with dilbit.

The survey identified a diversity of toxicity test methods, a lack of detailed reporting of methods, and an inconsistent use of terminology to describe test solutions, all of which hindered comparisons of toxicity among oils, fish species, and environmental conditions. Although most studies were technically sound, they often modified standard methods to suit specific study objectives without providing sufficient details and rationales for the changes reported. Their focus on site-specific conditions limited their applicability to Environmental Impact Assessments (EIAs) and ERAs of oil spills under different scenarios. Fortunately, there is an emerging consensus that test results can be compared when there are sufficient chemical analyses of test solutions to relate measured concentrations of oil in water to measured effects, even when test methods are not described in detail. Chemical analyses have also demonstrated that oil concentrations decline with time during most tests, and that chemical analyses of test solutions do not discriminate between dissolved and particulate hydrocarbons. Therefore, the true toxicity of oil dissolved in water may often be underestimated, adding uncertainty to estimated risks of oil spills.

This review updates the CROSERF protocols with recommendations to overcome specific issues with dilbit. The advantages and disadvantages of various methods are reviewed and a proposed framework is provided on experimental designs, physical and chemical characterization of test oils, preparation of physically- and chemically-dispersed oil, characterizing test solutions, and toxicity testing. Research needs are presented to improve experimental designs, the preparation and toxicity testing of oil solutions, the chemical characterization of test oil and oil solutions, and test requirements that recognize the unique characteristics of dilbit and other crude and refined oils.

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