Improving the design and conduct of aquatic toxicity studies with oils based on 20 years of CROSERF experience

The goals of the manuscript were to:•build upon 20+ years of experience to update the existing CROSERF guidance for conducting aquatic toxicity tests with petroleum and petroleum-derived products and•to improve the experimental design of laboratory ecotoxicity studies for use in hazard evaluation and development of quantitative effects models that can then be applied in spill assessment. Key issues discussed and considerations for experimental designs include:○species selection (standard vs field collected),○test chemical (single compound vs whole oil),○exposure regime (static vs flow-through),○exposure metrics,○toxicity endpoints, and○quality assurance and control.•Several research needs were identified including:○The need for additional single species acute and chronic toxicity data developed by today's scientific standards,○The need for time-course data to inform mode-of-action concerns○Additional information regarding the composition and toxicity of spill response agents○Improved characterization of bioassay conditions and exposure solutions to be useful for toxicity modeling and impact assessment. Laboratory toxicity testing is a key tool used in oil spill science, spill effects assessment, and mitigation strategy decisions to minimize environmental impacts. A major consideration in oil toxicity testing is how to replicate real-world spill conditions, oil types, weathering states, receptor organisms, and modifying environmental factors under laboratory conditions. Oils and petroleum-derived products are comprised of thousands of compounds with different physicochemical and toxicological properties, and this leads to challenges in conducting and interpreting oil toxicity studies. Experimental methods used to mix oils with aqueous test media have been shown to influence the aqueous-phase hydrocarbon composition and concentrations, hydrocarbon phase distribution (i.e., dissolved phase versus in oil droplets), and the stability of oil:water solutions which, in turn, influence the bioavailability and toxicity of the oil containing media. Studies have shown that differences in experimental methods can lead to divergent test results. Therefore, it is imperative to standardize the methods used to prepare oil:water solutions in order to improve the realism and comparability of laboratory tests. The CROSERF methodology, originally published in 2005, was developed as a standardized method to prepare oil:water solutions for testing and evaluating dispersants and