科学美国人60秒 SSS 2013-09-25（在线收听）

 Cerumen, it's a lovely word a specially considering that's called ear wax. And we are not the only species that produce this stuff, some whales build up waxes along with lipids and carotene protein into what's called earplugs. And researchers now know that examining this  earplugs  tells them about whale's lifetime and exposure to pollution. Alternative layers of dark and light in the plugs corelate to the seasons feeling or migration,so the plugs are used to determine a whale's age, think treeings. In the latest study scientist analysed the earplug of an endangered blue whale killed by a ship near California. They found that levels of stress for months doubled over the whale's life. They also found evidence that the whale has been exposed to plasticize such as DDT with a highest level during the whale's first six months of live. The whale was likely exposed to the plasticize in his mother's milk.