DISPERSANTS (have a liberal note the spelling for you, for the future) are used to try to keep the oil from coming ashore. They are water-soluble, so they are hardly an air pollution risk when placed in the water.
Dispersants are a contact risk, when a drum of them is spilled, so they have to be handled carefully.
Once in the water column (that's "ocean," to you), they are a different sort of risk. Things that live in the water can be damaged or killed by dispersants. They also make clean-up a problem, since most oil is removed by water by using differences in density and solubility. Dispersants defeat that ability.