Second-Order Wins✓✓ 2 independent sources
America Banned Leaded Gas. Two Decades Later, Crime Collapsed.
Lead out of gas → measurable drop in crime one generation later (two independent studies agree)
Two independent research teams linked the phase-out to falling crime: Jessica Wolpaw Reyes estimated removing lead from gasoline can explain a large share of the 1990s violent-crime decline, while Aizer & Currie matched blood-lead records to school and juvenile-detention data and found higher childhood lead meant more delinquency decades later. One environmental regulation, two generations of downstream effects nobody put on the front page.
The US finished phasing lead out of gasoline in the 1990s — and economists tracking the generation that grew up lead-free found violent crime fell with it.