By Peter Montague
Pollution causes people to commit violent crimes, according to new research by Roger D. Masters and co-workers at Dartmouth College.
Sociologists have known for a long time that violent crimes occur more in some places than in others. Some US counties have rates of violent crime that are 30 times as high as others. The question is why some places have high crime rates and others don't. Masters says pollution is part of the answer.
Masters has developed what he calls the neurotoxicity hypothesis of violent crime. According to this hypothesis, toxic pollutants — specifically the toxic metals lead and manganese — cause learning disabilities, an increase in aggressive behaviour and — most importantly — loss of control over impulsive behaviour.
These traits combine with poverty, social stress, alcohol and drug abuse, individual character and other social factors to produce individuals who commit violent crimes.
Masters argues that such a hypothesis must pass five tests. He then demonstrates how the neurotoxicity hypothesis meets all five:
1) It must be shown that individuals who engage in criminal behaviour are more likely to have absorbed toxic chemicals than a comparable control population. Masters cites studies showing that low-level poisoning by lead, and by manganese, is associated with learning disabilities and attention deficit disorder, which are themselves associated with deviant behaviour.
Masters cites seven other studies showing that violent prisoners have significantly elevated levels of lead, manganese, cadmium, mercury or other toxic metals, compared to prisoners who are not violent.
2) The hypothesis must be able to predict future violent behaviour of young people exposed to toxins. Masters cites two prospective studies (and suggests we need more) showing that lead uptake at age seven is associated with juvenile delinquency and/or increased aggression in teenage and early adult years.
The largest study, of 1000 black children in Philadelphia, showed that both lead levels and anaemia were predictors of the number of juvenile offences, the seriousness of juvenile offences and the number of adult offences, for males.
3) Is there a biological basis for believing that lead, manganese and other toxic metals could cause a person to lose control over impulsive and aggressive behaviour? Here Masters cites a wealth of studies showing how lead and manganese cause changes in the development of the brain, and in the functioning of neurotransmitters in the brain.
Lead in the brain damages glia, a kind of cell associated with inhibition and detoxification. Manganese lowers levels of serotonin and dopamine, which are neurotransmitters associated with impulse control and planning. Low levels of serotonin in the brain are known to cause mood disturbances, poor impulse control and increases in aggressive behaviour — effects that are increasingly treated with Prozac.
Masters emphasises that children who are raised from birth on infant formula and are not breast fed will absorb five times as much manganese as breast-fed infants. Calcium deficiency increases the absorption of manganese.
A combination of manganese toxicity and calcium deficiency adds up to "reverse Prozac", Masters says.
Masters says toxic metals affect individuals in complex ways. For example, because lead diminishes a person's normal ability to detoxify poisons, lead may heighten the effects of alcohol and drugs.
4) For the neurotoxicity hypothesis to hold up, individuals must receive doses of toxic metals sufficient to be associated with violent behaviour.
Masters argues that, despite recent significant decreases in lead in the environment, in neighbourhoods where automobile traffic has historically been high, and in towns where industries have released large quantities of toxic metals for years, many local soils still contain toxic quantities of lead, cadmium and manganese sufficient to poison children who play in the dirt. He also says that ageing water delivery systems very likely contribute lead and manganese.
Masters argues that (a) children absorb up to 50% of the lead they ingest (compared to 8% for adults); (b) even low exposures in the womb and in early childhood can have permanent effects on intelligence and behaviour; (c) current lead levels are known to have direct effects on neurotransmitters that affect cognition and impulse control; and (d) the highest levels of lead uptake are reported in precisely the demographic groups most likely to commit violent crimes (inner city minority youths).
Masters emphasises the importance of studies showing a synergistic (multiplier) effect between toxic metals and poor diet. For example, uptake of lead is greatly increased among individuals who have a diet low in calcium, zinc and essential vitamins.
Thus, Masters argues, amounts of lead and manganese that wouldn't harm a well-nourished individual may poison undernourished children.
Masters cites federal studies to make the point that black teenage males consume, on average, only about 65% as much calcium as whites.
The calcium needs of pregnant or breast-feeding women are higher than average, which creates a particular problem for minority women. And non-Hispanic black women get only 467 milligrams of calcium per day, compared to 642 mg for white women, government studies show.
Because of increased manganese absorption by babies who drink infant formula and who are not breast fed, Masters considers infant formula toxic. White infants are more than three times as likely to be breast fed as black infants.
Masters cites studies showing that alcohol increases the uptake of toxic metals, at least in laboratory animals, and probably has a similar effect on humans.
5) If the neurotoxicity hypothesis is valid, then measures of environmental pollution should correlate with higher rates of violent crime.
To test his hypothesis, Masters acquired data from the FBI for violent crimes in all counties of the US. He correlated this with data on industrial releases of lead and manganese into the environment of each county, using data from the US Environmental Protection Agency's TRI (toxic release inventory) database.
He also examined demographic and socioeconomic variables for each county.
Masters split all US counties into six groups — those with and without industrial lead releases; those with and without industrial manganese releases; and those with higher-than-average or lower-than-average rates of alcohol-related deaths.
After controlling for all the conventional measures of social deterioration, Masters found that counties having all three measures of neurotoxicity — lead, manganese, and high alcohol — have rates of violent crime three times the national average.
In other words, environmental pollution and alcohol have a strong effect on violent crimes, completely independent of any of the "traditional" predictors of violent crime (poverty, poor education etc).
As Masters says, neurotoxicity is only one of many factors contributing to violence, but he believes it may be especially important in explaining why violent crime rates differ so widely.
Masters says that traditional sociological approaches cannot explain why the availability of hand guns or drugs triggers violent behaviour in only a small proportion of the population, a proportion that varies greatly from place to place. Part of the explanation may be the way the physical environment affects brain chemistry and behaviour, Masters says.
"The presence of pollution is as big a factor as poverty", Masters said recently in an interview in New Scientist magazine.
"It's the breakdown of the inhibition mechanism that's the key to violent behaviour", he says. When our brain chemistry is altered by exposure to toxins, we lose the natural restraint that holds our violent tendencies in check, Masters believes.
[From Rachel's Environment & Health Weekly. Like Green Left Weekly, Rachel's is a non-profit publication which distributes information without charge on the internet and depends on the generosity of readers to survive. If you are able to help keep this valuable resource in existence, send your contribution to Environmental Research Foundation, PO Box 5036, Annapolis, Maryland 21403-7036, USA. In the United States, donations to ERF are tax deductible.]