“Hair ‘is really a vault of information,’ says Ken Smith, a demographer at the University of Utah. He should know—he’s among a team of scientists that analyzed chemicals found in hair samples collected over the course of more than a century in research published on February 2 in Proceedings of the National Academy of Sciences USA. Incredibly, Smith and his colleagues found that exposure to lead—a dangerous heavy metal—has fallen by a factor of more than 100 since the 1960s.”

From Scientific American.