> A 1994 study had indicated that the concentration of lead in the blood of the U.S. population had dropped 78% from 1976 to 1991.
https://en.wikipedia.org/wiki/Tetraethyllead#Controversy_and...
"It’s important to emphasize that the lead-crime hypothesis doesn’t claim that lead is solely responsible for crime. It primarily explains only one thing: the huge rise in crime of the 70s and 80s and the equally huge—and completely unexpected—decline in crime of the 90s and aughts."
https://www.motherjones.com/kevin-drum/2018/02/an-updated-le...
I would wager the reasons for the increase in the late 60's is similar to the recent rise, and that it has nothing to do with lead.
There were WAY fewer cars back then. So, you need to look at emission per car*number of cars.
A lot of pollution problems peaked in the 1970's--that's the whole reason why a raft of environmental legislation was enacted at that point.
Unlikely that there's enough of this type of exposure to be a real factor. Even this study finds that it affects children living within 500m of a civilian airport and that the level of lead detected was "not especially large."
There may be an argument for phasing out leaded avgas, as no amount of lead exposure is good, but it's not likely to have an impact on overall violence in an area, even assuming that lead has anything to do with that in the first place.
While there will always be smash and grabs and the like, I think smart criminals have realized there are steep penalties for muggings, the response time is much lower than it was previously, and even if you succeed you won't get much out of it since the CCs will soon be cancelled, the phone is IMEI locked, and the wallet only has a twenty.