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PRI's Environmental News Magazine

Crime and Heavy Metal

Air Date: Week of June 6, 1997

A group of researchers at Dartmouth College says the presence of lead and that of a similar heavy metal, manganese, in a community is directly correlated with the rates of violent crime. Roger Masters is a professor of political science at Dartmouth whose team recently looked at the government's Toxic Release Inventory. Comparing levels of lead and manganese emissions with crime statistics, the researchers came up with some remarkable trends.


CURWOOD: This is Living on Earth. I'm Steve Curwood. There is new and disturbing news on the problems associated with lead poisoning in children. Research over the last 2 decades has linked childhood exposure to lead with altered brain development, hyperactivity, learning disabilities, and lowered IQ scores. More recent research has linked high school drop-out rates, aggression, and juvenile delinquency to the metal. Now, researchers at Dartmouth College say the presence of lead and that of a similar heavy metal, manganese, is directly correlated with rates of violent crime. Roger Masters is a professor of political science at Dartmouth. His team recently looked at the government's Toxic Release Inventory, compared levels of lead and manganese emissions with crime statistics, and came up with some remarkable trends.

MASTERS: What we found was that in the counties where there is no record of environmental pollution from either lead or manganese, the crime rate is 278 per 100,000 per year. That's all the violent offenses for homicide, aggravated assault, sexual assault, and the like. In the counties where both kinds of pollution are present, the crime rate is 578 per 100,000. That's more than twice as high. Now, as soon as you have a correlation like that you check, could it happen by accident. That could happen by accident for each of those metals less than once in 10,000 times, which is the level of correlation significance that my colleagues in social science would die for. But when you have a correlation coefficient that doesn't tell you everything, there may be something else involved, and we've checked all the statistical approaches that I know of and find that controlling for income, population density, ethnicity, unemployment, there still is a significant effect of the presence of pollution on crime rates in the United States.

CURWOOD: So what you're saying is if you live in a neighborhood, if you live in a county, regardless of your income, regardless of your race, regardless of the fact if it's the inner city or the countryside, if there's more lead and manganese in your county, you're more likely to commit a crime or be a victim of a crime?

MASTERS: That's correct. I like to think of this, and this is a standard concept, as a risk factor along with other risk factors.

CURWOOD: Dr. Masters, we're used to thinking that violent crime is generally associated with things like poverty, drug use, the breakdown of family, you know, the bad home, the bad apple. Are you saying we're wrong?

MASTERS: No. The factors that we traditionally associate with crime are probably clearly associated with crime. Not every poor individual goes out and kills someone. Not everyone from a broken home kills someone. What we have to understand is that human behavior is usually the result of many factors, and that most of the competing explanations are probably all correct. My concern is that we need to look at why it is that within some poor families that are broken, where people are unemployed and living in poor environments, there are criminals and in others there are not criminals.

CURWOOD: Now, your research shows that alcohol is involved here. What's the relationship of alcohol to this?

MASTERS: It turns out that many human beings have aggressive impulses, and the reason why we're not all violent is not that we never imagine hurting somebody. Lots of people imagine violent behavior. But we usually inhibit it. And so, when you look at violent behavior, it's useful to think of it as a loss of the control of inhibition over your impulses. Now, alcohol leads people to lose control. There is a good deal of evidence that one of the effects of these toxic metals in the brain is to down-regulate or destroy the capacity of the brain to deal with other toxins, so that if you've got lead, manganese -- and there are other toxic metals that also have this kind of effect, cadmium -- in the brain, then the effect of alcohol is much greater than it would otherwise be. And what we find is that counties with higher levels of alcoholism also have much higher crime rates, and that this interacts with the existence of the toxic metals. So that in the counties that have higher than average rates of alcoholism and the release of both toxics, the crime rate is 3 times that of the national average.

CURWOOD: What are the social implications of what you're saying?

MASTERS: One of the consequences is the realization that studying biology gives us better control over outcomes. In the last 4 years there have been annual declines in crime rate. And at first people said well, there's better policing in New York, but that doesn't lower the crime rate in Toledo. What's interesting is that it takes about 16 years to grow a criminal, and if you look at the time series, we are now gaining the benefit, if I'm right, in having taken lead out of gasoline.

CURWOOD: You're saying that these recent declines that we see in crime rates can be attributed basically to lack of atmospheric lead from car exhaust now in this country.

MASTERS: I'm not sure of that. What I would suggest is that it's the kind of factor that might explain not only the decline in crime rates, but a small but significant increase in SAT, which has been mysterious, and a small but significant decrease in teenage pregnancies, which has been associated with attention deficit disorder, which in turn has been associated with lead. So we don't know why crime has fallen across the country, but the usual explanations don't explain the kind of statistics that we're seeing in the United States.

CURWOOD: Isn't it true, Professor Masters, that the greatest exposure of lead in this country is to deteriorating paint in houses, and historically has been from gasoline and in the soil outside? Looking at the Toxic Release Inventory for lead and manganese, is that really giving us an accurate picture of the exposure of lead in this country?

MASTERS: Certainly not. There are a number of ways in which individuals are exposed to lead and manganese, and the presence of factories is only one of them. I have no evidence at all that there's any one measure that can catch all of the absorption of lead. We are beginning a study where we have some data on actual uptake of lead in individuals, and we can compare that to the crime rate. But I think that the basic lesson of our research may be much simpler. It's that instead of wondering if we have every possible source of lead, and every possible source of manganese, to begin to think about ways of using our knowledge of brain chemistry to prevent or reduce rates of crime.

CURWOOD: What would you have us change now, in our society? How can we take this information that lead and manganese and perhaps other heavy metals are related to our crime rate, and reduce our crime rate?

MASTERS: One of the key factors in the absorption of toxic metals seems to be diet, and especially deficiencies in basic elements such as calcium and zinc. What this means is that better diet may be an absolute wonderful thing for reducing crime rates, increasing educational performance, and improving the lives of people who are both poor and exposed to toxic elements like lead and manganese. I have in mind such things as school lunches, better dietary supplements. There are a whole set of issues connected with prenatal care to make sure that pregnant mothers do not absorb toxics and transmit them to the fetus. I think that there are a number of traditional approaches to good health that can have a huge effect once we realize that they are directly connected to the way in which individuals have become vulnerable to environmental pollution. Let me give a simple example from a laboratory study. Rats were put in an environment where there was manganese, and when they had a good diet, the rats didn't absorb it. If the rats had a bad diet and there was no manganese, they were normal. If they had a bad diet and there was manganese in the environment, then they got manganese in their brains. What I'm suggesting is that the evidence is quite clear that if your diet is deficient in basic elements like calcium, and if there's a pollutant in the environment, then that chemical gets in the brain.

CURWOOD: What's your next step here? How do you plan to get more confirmation of this?

MASTERS: The next 2 things that I plan to do are to look at data we have from one state on individual rates of lead in the blood of children, to find out by town whether environments in which lead is actually being absorbed by children have higher crime rates. We're going to be looking at our national data in the United States to see the effect of toxicity on health, particularly death from heart disease and cancer. And I hope to be looking at some foreign data to find out whether, in foreign countries as well, communities where there's environmental pollution have higher crime rates.

CURWOOD: Okay. Well, I want to thank you for taking this time with us. Roger Masters is Professor of Political Science at Dartmouth College. Thank you, sir.

MASTERS: Thank you very much.



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