Oil is a mixture of many different chemicals.
Not only does each of these have its own toxicity, but each also behaves differently in the environment. Some components are much more volatile than others, and so they tend to evaporate more rapidly when oil is spilled. Some are more easily broken down by microbes on the beaches. Sunlight can also degrade oil components. In Prince William Sound, our chemists tell us that the remaining Exxon Valdez oil ranges from very weathered to relatively fresh .