According to recent articles published by ScienceNOW and Smithsonian, researchers have discovered that the taste buds of cetaceans (whales, dolphins, porpoises) only sense salty flavors. The other receptors have been shut off or have mutated. Thus, they are likely not able to taste unnatural flavors in the water, such as toxins, which are often bitter. As the ScienceNOW article points out, and we emphasize here when discussing how cetaceans eat, these animals swallow their food whole, thus eliminating much of the need to taste the food.
The two articles referenced above are based on research published in Genome Biology and Evolution. Zoologist Huabin Zhao of Wuhan University in China led the study.