Narrator: Who do you cling to? That's the question during an oil spill. This is Science Today. One common way to clean up an ocean oil spill is to spray chemicals called dispersants. Chemist Ron Tjeerdema of the University of California, Santa Cruz says dispersants don't disperse oil so much as cling to it, taking it out of contact with birds and marine mammals. But if dispersants are sprayed where there's no oil, they can be just as harmful as the spill.

Tjeerdema: What they tend to do is they like to adhere to things. They like to stick to surfaces. Well, marine organisms provide surfaces for them in water. And what they can do is they can literally coat marine organisms and thus block their ability to respire oxygen from water. And thus be quite lethal.

Narrator: But not if there's any oil around.

Tjeerdema: The presence of oil reduces the toxicity of dispersants because the oil sort of attracts the dispersant away from the organisms. Where the dispersant has sort of the choice of glumping on to either oil or organisms, it goes after the oil, leaves the organisms alone.

Narrator: For Science Today, I'm Steve Tokar.