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 behavior. 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. If it is valid, the neurotoxicity hypothesis must be able to predict future violent behavior of young people exposed to toxins. The largest study, of 1000 black children in Philadelphia, showed that both lead levels, and anemia, were predictors of the number of juvenile offenses, the seriousness of juvenile offenses, and the number of adult offenses, for males. 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.
Different pollutants harm the brain differently.
Lead in the brain damages glia, a kind of cell associated with inhibition and detoxification. Manganese has the effect of lowering levels of serotonin and dopamine, which are neurotransmitters associated with impulse control and planning. Masters emphasizes that children who are raised from birth on infant formula and who are not breast fed will absorb five times as much manganese as breast-fed infants. Calcium deficiency increases the absorption of manganese. Masters says toxic metals affect individuals in complex ways.