On the other hand, Japan, which had lots of lead-spewing cars and extremely dense population, and thus should have been a prime victim of lead poisoning, never experienced a Great Freakout. So, that's one strike against the theory.
In general, I'm skeptical of there being a "Single Bullet" explanation for the the 1960s, but it's worth looking at this in some detail, more than I can muster here, but I'll take a first look at it.
More generally, as Steven D. Levitt pointed out on his Freakonomics blog:
"Recently, however, Jessica Wolpaw Reyes at Amherst has put together what appears to me to be the most persuasive evidence to date in favor of a relationship between lead and crime. Rather than looking at a national time-series, she tries to exploit differences in the rates at which lead was removed from gasoline across states. I haven’t read her paper with the care that a referee would at an academic journal; but, at least superficially, what she is doing looks pretty sensible. She finds that lead has big effects (and, for what it’s worth, she also confirms that, when controlling for lead, the link between abortion and crime is as strong or stronger as in our initial study, which did not control for lead.)"
The problem for how much confidence to place on this paper is that murder is the most accurately measured crime. Other crimes vary dramatically in likelihood of being reported to the police across time and place, but attention must be paid to a dead body with a hole in it.
Second, the big increase in the murder rate was from roughly 1965-1975. She assumes a 22 year lag, from postnatal exposure to lead, so that was from births in 1943 to 1955, but she says that lead poisoning due to leaded gasoline didn't peak until 1970, so how come the murder rate didn't keep going up? It bounced around a lot after that, but the Great American Freakout was basically from the mid-60s to the mid-70s. .
Third, when looking at the crime fall in the 1990s, this study appears to have the same flaw that dragged down Levitt's abortion-cut-crime theory -- a failure to look carefully at crime rates by age cohort, combined with an intoxication with analyzing complex state-level data that leads to a failure to do simple national-level reality checks. (She was clearly influenced by Levitt, so this shortcoming is not surprising.) Wolpaw Reyes simply assumes a 22 year lag between lead poisoning around the time of birth and the violent crime rate. But, we can easily look at more detailed data for different age cohorts, which shows that the crime decline of the 1990s began among older individuals, not among the younger people supposedly benefiting from lower lead or higher abortion.
If you assume a 22 year lag to violent crime, then this graph looks great because the murder rate started to fall after about 1991.
But, that's the same mistake Levitt made way back in 1999: he forgot to look at the crime rates among narrower age cohorts. For the 17-and-under crowd, the two worst years were 1993-94. In other words, they were born when lead pollution had already fallen by almost half (just as they were born when legal abortion was close to its peak, which is a problem for Levitt's theory).
Here's the relevant homicide rate graph showing that for the 14-17 year-old cohort, the murder rate moved in exactly the wrong direction for the first 6-7 years of the great lead decline.
Similarly, here's the non-lethal serious violent crime rate for 12-17 year-olds as reported by the government's massive annual survey of crime victims. It too shows the crime rate for the relevant cohort moving in the wrong direction.
"3. The use of fluosilicic acid (H2SiF6) to fluoridate public water supplies significantly increases the amounts of lead in the water (whereas the use of sodium silicofluoride (NaSiF6) or sodium fluoride (NaF) does not."
A simple suggestion for further research is that America's Environmental Protection Agency keeps a list of SuperFund CleanUp sites polluted by lead. Typically, these are locations with lead smelters, mines, factories, or dumps. It would be a fair amount of work, but hardly impossible to compare crime rates in small towns with names like Smelterville, Leadville, Galena, and so forth to similar towns with no point sources of lead pollution.
I've read newspaper accounts of the lawsuit against the smelter firm in a small town in Missouri. The plaintiffs argued that lead pollution was damaging the children of the town -- yet, the plaintiffs didn't seem to emphasize high crime rates. Instead, the poisoned children were described as unenergetic, sluggish, and so forth.
Anyway, there is a lot of information available on the web from these kind of lawsuits, so I'd recommend anybody interested in the topic just read up on it.
(Wandering even farther afield, Jack D. Ripper was played, brilliantly, by Sterling Hayden, the stepfather of American Conservative editor Scott McConnell.)