The Generation of Water Accommodated Fraction (WAF) and Chemically Enhanced Water Accommodated Fraction (CEWAF): Development of an Updated Standard Protocol

Project: Research project

Project Details



The continued expansion of oil and gas development and transport in Canadian waters increases the risk of spills and potential impacts on aquatic ecosystems and organisms from both routine operations and accidental releases. In recent years, the most common methods used for preparing oil samples for aquatic toxicity testing have been WAFFootnote 1 and CEWAF.Footnote 2 However, large variations in toxicity study results for the same oils across laboratories may be due to differences in how oil solutions are prepared for testing, which affects their chemical composition. To address this issue, this project will evaluate the WAF and CEWAF generated using three reference oils (low, medium, and heavy), and the dispersantFootnote 3 COREXIT 9500A. The goal is to refine the method for producing test solutions to reduce variations in toxicity studies for different types of oil. Specifically, the research will:

  • measure the hydrodynamics in various mixing vessels using the magnetic stirrer to prepare oil samples;
  • measure the size, distribution, and concentrations of the oil droplets in water for three weathered oils (light, medium, and dilbit), with and without the dispersant;
  • propose improvements to the magnetic stirrer approach, or develop an alternative approach, to generate reproducible WAF and CEWAF (as measured by oil droplet size and other chemical factors) for different types of oil and solution volumes that might be required for toxicity testing in the future.

The results will contribute to the development of a revised standard method for evaluating the toxicity of heavy oils and other petroleum products for aquatic species, which is essential for assessing the use of dispersants versus other methods during oil spill response.

Effective start/end date4/1/183/31/19


  • Fisheries and Oceans Canada


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