“The bottom line, as Drum points out, is that “even moderately high levels of lead exposure are associated with aggressivity, impulsivity, ADHD, and lower IQ. And right there, you’ve practically defined the profile of a violent young offender.” [0]

Have never heard of this research/correlation, but pretty interesting how it holds across models.

[0] https://www.motherjones.com/environment/2016/02/lead-exposur...