Marine oil spills are frequently treated with dispersants to dispand oil and speed-up breakdown. Dispersants facilitate breakdown into tiny droplets that are more rapidly diluted and become more available for biodegradation. Because of their mode of action, dispersants can alone cause the disruption of biological membranes, and thus, are potentially dangerous for aquatic life. In addition, the mixture of oil and dispersant releases greater concentrations of toxic oil components (e.g. polycyclic aromatic hydrocarbons – PAHs). Consequently there is great concern surrounding the long-term impacts of oil spills and the use of dispersants on marine ecosystems.

The main objective of this study was to quantify how crude oil treated with dispersant affects embryo development of capelin, a keystone species in the Northwest Atlantic food web. In this study, capelin embryos were exposed to crude oil water (oil-to-water ratio of 1:9) and water mixed with the dispersant Corexit (dispersant-to-water ratio of 1:10 (10%) or 1:50 (1%)). Different lethal (survival at different embryonic development stages and hatching) and sub-lethal effects (heartbeat rate, larvae morphology and expression of certain genes) were studied. 

The higher tested concentration of chemically dispersed oil was lethal to capelin embryos within only 10 hours of exposure, and completely impaired their survival if exposed for longer periods. Sublethal effects, which can subsequently affect larval survival, were observed at concentrations 100 times lower. These concentrations are well within the range of what can be observed in the event of an oil spill. The study shows that in the event of an oil spill close in time and space to capelin spawning, the use of dispersants may increase the concentration of crude oil toxicants, and dispersant compounds, to levels that could significantly reduce embryo larval survival and later recruitment in affected areas.

See full article at Science Direct