Has lead poisoning driven Pakistan’s epidemic of violence? (updated)

Lead permanently damages young brains

The impact of lead poisoning is devastating, especially just before and after birth:

The nervous system of the fetus and infant is especially susceptible to lead, which can cross the placenta and penetrate the blood-brain barrier. Lead interferes with neuronal migration, cell proliferation and synapse formation during critical periods of early vulnerability. The consequences are loss of intelligence and disruption of behaviour. Because the brain has little capacity for repair, these effects are permanent and untreatable. The most recent research indicates that lead can damage the infant brain even at blood levels as low as 5 m/dl.

Exposure to lead leaves children less able to learn in school and makes them more likely to display aggressive, anti-social and hyperactive behaviour. Do read Kevin Drum’s excellent account of the evidence showing that even low levels of lead poisoning can lead to lower IQs and more violent behaviour.

Lead poisoning may have caused a global surge in violence

In the late 20th century, lead in petrol caused a significant increase in lead poisoning. And as people drove more (and spent more time idling in traffic), levels of violent crime went up, before falling a few decades after unleaded petrol was introduced.

In a 2000 paper (PDF) [Rick Nevin] concluded that if you add a lag time of 23 years, lead emissions from automobiles explain 90 percent of the variation in violent crime in America…

Nevin collected lead data and crime data for Australia and found a close match. Ditto for Canada. And Great Britain and Finland and France and Italy and New Zealand and West Germany. Every time, the two curves fit each other astonishingly well. When I spoke to Nevin about this, I asked him if he had ever found a country that didn’t fit the theory. “No,” he replied. “Not one.”

The worst impact is on cities – and especially on slums

Traffic is worst in cities and people live close to roads. The biggest and most congested roads cut through the poorest parts of these cities. Bad housing lets in more pollution, while children spend more time playing in the streets. Other sources of lead – from paint, pipes etc. – also tend to be worse here.

Violence saw the steepest increase and the steepest decline in cities. Last year, New York celebrated a full day without a murder, assault or any other incident of violent crime.  In 1990, 2245 people were murdered. In 2012, that had fallen to 419. Crime in the UK is now more than 50% below its peak in 1995, with London’s murder rate at a 42 year low.

Lead poisoning could be a significant factor driving Pakistan’s epidemic of violence

In 2002, a study of 430 children in Karachi (from Sadar in the city centre, two suburbs, a rural community, and Baba Island) found that 80% had blood concentrations over 10 mg/dl (twice the level now thought to be ‘safe’) and average levels of 15.6 mg/dl.

The children with the worst lead poisoning lived near busy traffic intersections, had poorly educated parents, lived in houses that opened into prevailing wind, and were more likely to eat food from street vendors. They were also more likely to use traditional remedies or makeup (e.g. surma), with very high concentrations of lead, or to live in houses that use lead paint.

If research linking lead to surging violence holds up, then lead poisoning could explain part of the epidemic of violence Pakistan is currently experiencing, especially in Karachi and other big cities.

Violence in Pakistan might fall rapidly after 2020

The United States started to phase out leaded petrol in the mid-1970s, a process that was substantially complete ten years later.

Pakistan acted later. There were four petrol-producing refineries in Pakistan at the turn of the century. They reduced lead content between 1997 and 2000 and phased it out between 2000 and 2002.

Given that car use and city centre congestion was increasingly rapidly at the time (and continues to do so), children with the highest levels of lead poisoning will be reaching adulthood throughout this decade.

After 2020, however, young adults will have suffered much lower levels of antenatal and infant lead poisoning. Levels of violence could then fall dramatically if they follow the pattern seen in the United States and other developed countries.

We don’t know enough about the impact of lead on Pakistan or other fragile states

There was some research into the impact of lead poisoning around the time Pakistan began to remove leaded petrol from sale, but little ongoing work to understand the impact of lead’s legacy on educational achievement or violent behaviour (that I know of, at least).

I suspect this pattern is repeated for other low and middle income countries, where 99% of the children affected by lead poisoning are believed to live.

Does lead poisoning explain some of the very high levels of violence seen in Karachi and other Pakistani cities? And, if so, how great is the impact likely to be? When do levels of lead exposure suggest ‘peak violence’ is likely to be hit? And what are the policy implications?

The same question could be asked for other fragile and conflict-affected states, each of which will have experienced different levels of pollution in the years where leaded petrol was widely used and will have seen reduced use of leaded fuels start at differing dates.

Update: While the impact of lead on young brains is established, the links between lead poisoning and levels of violence are less well understood. Again, I recommend Kevin Drum’s review, but Scott Firestone and Paul Illing have written useful overviews of the evidence.

Illing points out how few studies we have to rely on and concludes that “this shows how little we know about the neurobehavioural effects of many chemicals and how difficult it is to investigate them.”

I find it staggering that we’re groping in the dark given that this could be one of the worst ever environmental catastrophes – and one that is still unfolding in the fastest growing cities in the world.