When the water is poor, people get sick: they have diarrhea; their growth is stunted; they die. When the air is poor, people get sick: they cough; they cannot leave their beds; they die. However, they do not look sick when there is lead in their blood. You cannot look at a child who has an unhealthy blood lead level (BLL) and say, "This is not right. Something must be done," because in most cases, there is nothing to see.
Lead (Pb) exposure—which is making headlines in the U.S. because of recent events in Flint, Michigan-- is a major source of critical environmental health risks. But the problem is subtle: Affected children do not perform as well in school. They are late to read. They are slow to learn how to do tasks. Perhaps a few more children are born with cognitive deficits. Perhaps these children have less impulse control. Perhaps they exhibit more violence.
These symptoms are not always understood as an environmental or a public health problem – or indeed a development problem. Instead, people will say it is an issue of morals or of education. They will discipline the children, and then they will take themselves to task and ask how and why they are failing to raise these children correctly. Furthermore, they will have no idea that the problem is in the children’s blood.
Young children are particularly vulnerable to lead exposure. Studies have documented that exposure leads to neuropsychological impacts in children--including impaired intelligence, measured as intelligence IQ losses--at blood lead levels even lower than 5 micrograms of lead per deciliter of blood (µg/dL). So, clearly, the effect occurs at even very low BLLs.