Birds are the most high-profile victims of oceanic oil spills, but fish suffer from these messy accidents, too. Even worse, a new study suggests, the chemicals commonly used to clean up oil spills make oil far more toxic to fish, particularly for eggs and young fish.
Oil and water don’t normally mix. So, when a truck, train, or ship accidentally dumps its cargo into a lake, stream or sea, the oil sits on top of the water and spreads across its surface. The slick substance then flows with the currents and tides, poisoning the animals it encounters along its way.
Another way to get oil off the surface is to use a chemical dispersing agent. These detergent-based substances cause oil to bead up into tiny droplets that can mix into the water and disperse into deeper layers. Underwater currents can then theoretically dilute the oil and its risk to the environment.
Dispersion spares surface-dwelling animals, such as birds and otters. But as oil drifts downward, it falls on fish and on the eggs that are stuck to surfaces or buried in the sediment.
To find out just how dangerous dispersed oil might be to fish, Peter Hodson, a fish toxicologist at Queen’s University in Kingston, Ontario and colleagues performed a series of laboratory experiments with beakers that were meant to simulate contaminated lakes. In all of the beakers, the scientists mixed water with diesel oil, then added newly hatched trout embryos. In some beakers, the scientists added a dispersing agent.
Their analyses, published in the journal Environmental Toxicology and Chemistry, showed that dispersants greatly increased the amount of hydrocarbons that could affect fish. In turn, that extra dose of exposure made the oil 100 times more toxic to the animals. Toxicity was measured as an elevated enzyme response in the livers of the fish.
Exposure to dispersed oil doesn’t kill a lot of fish, Hodson added. Instead, it either kills eggs before they hatch or leads to damage or deformities in juvenile fish. Compared to the horrifying appearance of oil-drenched birds on beaches, it can be hard to catch the attention of the public — or even of cleanup managers — with such subtle and hidden health effects.
– from discovery