Ward Collin P, Armstrong Cassia J, Conmy Robyn N, French-McCay Deborah P, Reddy Christopher M
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA.
National Risk Management Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH, 45268, USA.
Environ Sci Technol Lett. 2018 Apr 25;5(5):226-231. doi: 10.1021/acs.estlett.8b00084.
Chemical dispersants are one of many tools used to mitigate the overall environmental impact of oil spills. In principle, dispersants break up floating oil into small droplets that disperse into the water column where they are subject to multiple fate and transport processes. The effectiveness of dispersants typically decreases as oil weathers in the environment. This decrease in effectiveness is often attributed to evaporation and emulsification, with the contribution of photochemical weathering assumed to be negligible. Here, we aim to test this assumption using Macondo well oil released during the spill as a case study. Our results indicate that the effects of photochemical weathering on oil properties and dispersant effectiveness can greatly outweigh the effects of evaporative weathering. The decrease in dispersant effectiveness after light exposure was principally driven by the decreased solubility of photo-oxidized crude oil residues in the solvent system that comprises COREXIT EC9500A. Kinetic modeling combined with geospatial analysis demonstrated that a considerable fraction of aerial applications targeting surface oil had low dispersant effectiveness. Collectively, the results of this study challenge the paradigm that photochemical weathering has a negligible impact on the effectiveness of oil spill response and provide critical insights into the "window of opportunity" to apply chemical dispersants in response to oil spills in sunlit waters.
化学分散剂是用于减轻石油泄漏对环境总体影响的众多工具之一。原则上，分散剂将漂浮的油分解成小液滴，这些小液滴分散到水柱中，在那里它们会经历多种归宿和迁移过程。随着油在环境中风化，分散剂的有效性通常会降低。有效性的这种降低通常归因于蒸发和乳化，而光化学风化的影响被认为可以忽略不计。在此，我们旨在以泄漏期间释放的马孔多井原油为案例研究来检验这一假设。我们的结果表明，光化学风化对油的性质和分散剂有效性的影响可能大大超过蒸发风化的影响。光照后分散剂有效性的降低主要是由光氧化原油残渣在由COREXIT EC9500A组成的溶剂体系中的溶解度降低所驱动的。动力学建模与地理空间分析相结合表明，针对表层油的大量空中喷洒的分散剂有效性较低。总体而言，本研究结果挑战了光化学风化对石油泄漏应对有效性影响可忽略不计的范式，并为在阳光照射的水域应对石油泄漏时应用化学分散剂的“机会窗口”提供了关键见解。
