Williams presents a wide-ranging overview of the vulnerability of human intelligence and behavior to events that interfere with normal brain development. Importantly, Williams points out that any of of these factors by themselves can have devastating impacts, but that they often co-occur . These are often poor communities struggling to provide a nurturing, supportive environment for young children. The co-occurrences compound the effects of the factors because they interact. For example, iron, vitamin D and calcium deficiencies increase lead uptake.
Biological synergism becomes more significant when viewed in the social context of poorer countries.
Many dirty industries which require a small labour force, such as nuclear power stations, are deliberately sited in rural areas within poorer countries. This is more than a theoretical concern, as illustrated in debates unfolding in the 2000 US presidential election. Both candidates are pushing for holding schools financially accountable for poor performance. Williams also presents a devastating critique of the inadequacy of risk assessment as practiced by the US EPA and other countries' regulatory agencies to protect against the neurotoxicological impacts of contaminants.