Ken Smith

Rule Changes

Lead researcher on hair analysis study

For most of the twentieth century, Americans inhaled roughly two pounds of lead per person annually from car exhaust alone. A new University of Utah study analyzing century-old hair samples confirms the scale of this unintentional mass poisoning—and the dramatic reversal that followed. Lead concentrations in human hair dropped from 100 parts per million before the 1970s to less than 1 part per million today, a 100-fold decline documented through specimens preserved in family scrapbooks.

Updated Feb 7