Violent behavior: consider role of environmental toxins

Explanations of violent behavior too often overlook environmental toxins, a new research review concludes.

The authors, David Carpenter and Rick Nevin, cite evidence showing that lead, arsenic, methyl mercury, and a variety of chemicals can reduce IQ. They note that in addition, lead and methyl mercury exposure can cause behavior changes including short attention span, hyperactivity, and impulsive antisocial behavior. Behavior and attention deficits, they point out, are also reported in children with heavy exposure to PCBs and dioxins as well as those exposed to pesticides.

The researchers note that studies clearly reveal an association between low IQ and violence. Theories suggesting that this link is due to genetics, they say, overlook the role of toxins such as lead—which is known to both reduce IQ and increase the risk for delinquency. They cite Nevin’s earlier research (see related article, Crime Times, 2007, Vol. 13, No. 3, Page 1) strongly correlating changes in blood lead levels with rising and falling crime rates in a range of countries across several decades.

“Recent USA incarceration rate trends are consistent with lead exposure trends,” they add, “resulting in a prison population increasingly dominated by older, life-course-persistent offenders.” They note that incarceration rates dropped between 2000 and 2006 for men under 30—a pattern predicted by reductions in preschool blood lead levels since the mid-1970s—while rates continue to rise for men over 40, who were born when rates of lead poisoning were very high.

“Our conclusions that environmental exposures contribute to violent behavior are not meant to discount other factors,” they say. “Clearly many children exposed to contaminants during development do not go on to become criminals. There are undoubtedly genes that contribute to susceptibility to violent behavior, just as there are genes that determine susceptibility to development of cancer consequent to chemical exposure.” In addition, they say, social factors undoubtedly interact with environmental factors to influence violent behavior.

“Our point, however,” they say, “is that while socioeconomic status, genes, poverty, low IQ and other factors have been widely discussed in relation to violent behavior, there has been little, and totally inadequate, attention given to the role of early life environmental exposures.” For instance, they point out, researchers focus on the sociological impact of poverty—but poverty also greatly increases exposure to brain-harming environmental toxins.

The researchers conclude that if research continues to support a strong link between environmental contaminants and violent behavior, “the most effective way to fight crime may be to prevent exposure to these contaminants.”