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Comment by outworlder | Hacker News Reader

But lead by itself can't be the major factor behind the crime drop. Countries such as Brazil have banned leaded gas even before the United States, and crime rates are still rising dramatically.

It seems clear that other factors play a more important role. Things like police effectiveness, or economics.

Edit: reference for lead ban dates: https://en.wikipedia.org/wiki/Tetraethyllead

Crime: http://en.wikipedia.org/wiki/Crime_in_Brazil

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A 1989 ban means people now in their 20s were young children in an environment with use of leaded fuel.

This article has some data about lead levels in children in Brazil: http://www.scielosp.org/scielo.php?script=sci_arttext&pid=S1...

In Brazil, Teixeira (32) has found that 11% of pipes used in the water distribution systems of 100 schools in São Paulo present lead levels above the limit considered safe by the WHO. In 2% of the water samples, the lead level was found to be five-fold higher than the highest acceptable value (< 10 µg/L, according to the WHO), thereby threatening the neuropsychiatric health of children.

Several studies have shown that high BLL in preschool children are strongly correlated with high lead levels in house dust (33-35). This association has been attributed to dust intake from the frequent hand-to-mouth behavior of young children. Flaking lead-based paint, road dust, garden soil and airborne lead-bearing particles are believed to be the sources of lead in household dust (36).

Leaded gas has caused more exposure to the metal than any other source worldwide (37). According to the São Paulo State Health Department (19), about 80% of the lead found in urban air samples before 1982 was derived from leaded gas. Car battery manufacture is the main source of secondary lead (38), but other sources cannot be discarded.

None of that is to say that lead is the only factor of course, just that I don't think your data disproves the theory that lead plays a significant part.

> just that I don't think your data disproves the theory that lead plays a significant part.

Exactly: (Lead => Crime) =/> (Crime => Lead).

The exact lag time doesn't matter.

If lead was banned at different times in different countries, the bans can't be responsible for a crime drop that happened at the same time.

Lead bans in America varied by state, the end date on that wikipedia page is a misleading number in that leaded gasoline use had been substantially reduced starting many years earlier. There was a major drop in leaded gasoline starting in the early 70s, by 1980 it was down over 50% from peak. By 1986 it was down over 90%.

I can't speak to the implementation of lead reduction leading to the outright ban in Brazil, but in the USA the outright ban was more of an after-the-fact recognition of the reality rather than an enforcement action.

Oblig link on "after-the-fact-recognition": http://www.wired.com/wiredscience/2013/01/looney-gas-and-lea...

You misunderstand. I meant the federal law was an after-the-fact-recognition of what many states had already done. Kind of like the way DOMA (defense of marriage act) was struck down by SCOTUS only after a bunch of states started recognizing gay marriage or how marijuana is likely to be legalized at the federal level only after enough states have already legalized it.

When was it effectively phased out in Brazil, though? Leaded gasoline was mostly gone in the US by the 1970s and there was a 20 year lag before the crime rate started dropping. The wikipedia article says lead was banned in the US in 1995, but it was definitely not widely available.

However, if lead was widely used in Brazil right up until the ban date there (1989) then it would stand to reason that the crime rate wouldn't start dropping for another six or seven years.

I was buying leaded gas in Indiana as late as 1990, and had no trouble finding it in the general Illiana area. I don't think it's fair to say it was "mostly gone" in the 70s.

[By 1979 half of the gasoline in the US was unleaded](http://66.147.244.135/~enviror4/about/ethyl-leaded-gasoline/...). So by the early eighties it was mostly gone. So yeah, I slightly misspoke saying it was mostly gone in the 70s, but it was halfway gone by then.

> But lead by itself can't be the major factor behind the crime drop. Countries such as Brazil have banned leaded gas even before the United States, and crime rates are still rising dramatically.

This is not logically sound. Brazil could have other factors which increase crime more than getting rid of lead reduces it. The fact that Brazil's crime has increased does not, in any way, tell us that the lead ban couldn't possibly be a major factor in the US's drop in crime.

There are other sources of environmental lead exposure besides leaded gasoline. Brazilian enforcement of environmental protections may not have been as successful as the US EPA was, especially in the past.

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