NYC cleaned up shortly after gas stations stopped selling leaded gas. Crime was significantly less in a short period of time. "it’s not just New York that has seen a big drop in crime. In city after city, violent crime peaked in the early ’90s and then began a steady and spectacular decline. Washington, DC, didn’t have either Giuliani or Bratton, but its violent crime rate has dropped 58 percent since its peak. Dallas’ has fallen 70 percent. Newark: 74 percent. Los Angeles: 78 percent." https://www.motherjones.com/environment/2016/02/lead-exposur...