Inner Ear.

http://en.wikipedia.org/wiki/Ear

There are two principal damage mechanisms to the inner ear in industrialized society, and both injure hair cells. The first is exposure to elevated sound levels (noise trauma), and the second is exposure to drugs and other substances (ototoxicity).

In 1972 the U.S. EPA told Congress that at least 34 million people were exposed to sound levels on a daily basis that are likely to lead to significant hearing loss.The worldwide implication for industrialized countries would place this exposed population in the hundreds of millions.