The use of the water-accommodated fraction (WAF) approach for the preparation of exposure systems of complex substances such as petroleum products has been a standard way to perform aquatic toxicity tests on these substances for over 30 years. In this Commentary, we briefly describe the historical development, rationale, and guidance for the use and reporting of the WAF approach to assess complex substances. We then discuss two case studies, with coal tar pitch and kerosene/jet fuel, which illustrate challenges from regulatory authorities in Europe and the United States when using the WAF approach. We describe how the WAF approach is the only currently known method for testing the toxicity of the whole of a complex substance, even when some of its constituents remain unknown; it accounts for differences in the solubility of the constituents within a complex substance; and use of loading rates to describe any toxic effects is a unifying concept that allows direct comparison with releases of readily soluble substances in hazard assessment and chemical classification.

在过去的30多年中，使用水混溶物（WAF）方法制备复杂物质（如石油产品）的暴露系统一直是对这些物质进行水生毒性测试的标准方法。在本评论中，我们简要介绍了使用和报告WAF方法评估复杂物质的历史发展，原理和指导。然后，我们讨论使用煤焦油沥青和煤油/喷气燃料的两个案例研究，这些案例说明了使用WAF方法时欧美监管机构的挑战。我们描述了WAF方法如何是目前唯一已知的用于测试复杂物质整体毒性的唯一方法，即使其中某些成分仍然未知。它解释了复杂物质中各成分溶解度的差异；用负荷率描述任何毒性作用是一个统一的概念，可以在危险性评估和化学分类中直接与易溶物质的释放进行比较。