In fact one of the lead researchers did a soil survey around New Orleans, and then compared that to the local police's crime hotspots map, there was a good correlation with contaminated soil and violent neighborhoods.
Not that I don't think that may be linked, but correlation≠causation, and in this instance it could be that (say) older neighbourhoods that have been longer exposed to pre-1992ish leaded car fumes are possibly more likely to be both poorer and more crime-ridden than more recent greenfield housing developments (and quieter roads) built after then.
With any luck, the researchers normalised for this sort of thing. If they could. But it's a thing to think about, if they didn't.
If it was just that data point then sure. Except we have multiple studies at
each of the
(1) personal level - mapping individual lead exposure to the behavior
(2) neighborhood levels - mapping localized lead exposure to the
same behaviors found in
individuals exposed to lead.
(3) studies at the city vs city level
(4) studies at the state vs state level
(5) studies comparing nations
(6) time-based as well as location-based correlations
So yeah it's pretty well established. I also out of interest once looked up a 1995 map of nations that hadn't phased out leaded gasoline at that point, here:
http://www.bay12forums.com/smf/index.php?topic=146257.0At that point in time, when I wrote that, the top 4 nations for homicide were "Honduras, Venezuela, United States Virgin Islands and Belize". While the only Western Hemisphere nations that
hadn't got rid of leaded gasoline by 1995 were Honduras, Venezuela, United States Virgin Islands, Belize, Bolivia, Paraguay. See, there's quite a large overlap in the categories of "places with leaded gasoline until recently" and "murder hellholes". Bolivia and Paraguay probably dodged this bullet, since they are landlocked nations without a port city which would be a focal point for urbanization, and thus smog concentration.