New evidence that dispersants are bad news for fish

Detailed study shows that fish exposed to oil-dispersant mix are less able to respond to subsequent environmental challenges

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Followup studies after the 2010 Deepwater Horizon oil spill call into question the extensive use of chemical dispersants. Photo courtesy NOAA.

By Summit Voice

FRISCO — A new European study once again shows that using dispersants to treat oil spills can be bad news for many marine organisms, even as it prevents massive slicks from reaching the shoreline.

The results of the study will be presented formally at the July 6 meeting of the Society for Experimental Biology meeting in Valencia. The increased contamination under the water reduces the ability for fish and other organisms to cope with subsequent environmental challenges, the research team found.

Led by professor Guy Claireaux, of the University of Brest,  the biologists for the first time looked at the effects of chemically dispersed oil on the performance of European seabass to subsequent environmental challenges.

The researchers designed swimming challenge tests in an ‘aquatic treadmill’, similar to the tests used in human medicine for health diagnosis. They analyzed European seabass’ maximum swimming performance, hypoxia tolerance and thermal sensitivity as markers for their capabilities to face natural contingencies.

They then exposed the fish to untreated oil, chemically dispersed oil or dispersant alone for 48 hours. During the following 6 weeks they measured individual growth and then once again analysed the seabass’ performance in the swimming challenge tests.

Oil exposure impacted the ability of fish to face increased temperature, reduced oxygen availability or to swim against a current and these effects were further aggravated with the addition of the dispersant. The dispersant alone had no effect on the ability of fish to face the challenge tests.

“An oil slick reaching the shore is not good for tourism and organisms living on the coast line,” Claireaux said. “Treating the slick at sea will avoid or reduce these problems affecting surface animals (birds and marine mammals). On the other hand, oil dispersion will increase the contamination of the water column and the organisms that occupy it.”

Though applying dispersants at sea may reduce the environmental and economic impacts of an oil spill reaching the shoreline, these results show that the choice of response deployed to deal with a spill involves a trade-off between the effects at the surface and in the water column.

Previous studies related to the Deepwater Horizon oil disaster in the Gulf of Mexico also showed that the oil-dispersant mix is more easily absorbed by aquatic organisms.

A lab study done by scientists with the Georgia Institute of Technology and Universidad Autonoma de Aguascalientes, Mexico, showed that the oil-dispersant mix was up to 52 times more toxic to tiny rotifers, microscopic grazers at the base of the Gulf’s food chain.

Scientists with the University of Miami Rosenstiel School of Marine & Atmospheric Science found that that even low-level, short-term exposure to traces of oil remnants causes deformities and impairs the swimming ability of fish.

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