30-year-old lead finds its way into the trendy urban chicken business

The United States began phasing out the use of tetraethyllead in gasoline in the mid 1970s (though it's still used in aviation and race car fuel). The pollution from TEL-enhanced gas, however, continues to linger in the soil, especially in cities, where concentrations of tailpipe emissions were higher. A recent study of New York City chickens found that lead from the soil was showing up in detectable levels in the chickens' eggs. The dose is low (though you probably don't want young children eating lots of those eggs), but it's a great example of how the effects of pollution don't vanish just because the pollution ends.

Lead and violent crime — why a good hypothesis isn't proof

We know that lead exposure can be dangerous. We know that it can cause brain damage. But what levels are dangerous. How does that damage express itself? And how do you separate the effects of lead poisoning from a whole host of other potentially dangerous, damaging factors? Last week, Mother Jones had a well-done article about research that is drawing connections between leaded gasoline and the crime wave of the mid 20th century. That's a hypothesis. It's a hypothesis with a lot of correlational evidence. But it's not proof. I recommend reading public health researcher Scott Firestone's excellent article that delves into the details of the studies from the Mother Jones story. It's a great look at the lines between public health as a science and public health as activism and it helps shine some light on why seemingly airtight cases aren't always immediately acted upon.

Leaded gasoline and the 20th-century crime wave

Scientists are amassing evidence that suggests exposure to tetraethyl lead — the additive once used in almost all the gasoline sold in the United States — could account for the dramatic increase in crime that happened in this country between the 1960s and 1980s. As leaded gasoline was phased out, they say, children were exposed to less lead, leading to the decline in crime that began to really kick in in the 1990s.

This is the same curve of crime statistics that economist Steven Levitt, of Freakonomics fame, attributed to the legalization of abortion. Levitt's theory was that, after Roe v. Wade, there were fewer unwanted babies born into dire circumstances and, thus, fewer people to grow up on the path to criminal behavior. Levitt matched the rise in abortion rates to the decrease in crime, but frankly, there are a lot of things that you can correlate to the decrease in crime.

What makes the lead theory interesting is that correlations match not just at the national level, but at regional, and even neighborhood levels. Increases in lead relate to increases in crime — usually a couple of decades later. Likewise decreases in lead relate to later decreases in crime. What's more the same correlations exist in countries all over the world. Meanwhile, we know that lead has big impacts on growing bodies — it affects brain function, it's linked to hyperactivity, difficulty managing aggression, and lowered IQ.

Correlation isn't causation. But in this case they definitely seem to be winking suggestively at one another. Kevin Drum has an excellent piece on this at Mother Jones, working through a decade worth of research by multiple scientists that supports this disturbing conclusion. It really is possible that we, as a society, damaged a generation of children and caused a crime wave (not to mention the ongoing damage to kids that live in high-lead neighborhoods today).

Via Michael Mechanic