Lead, mercury, and arsenic may occur naturally in the earth, but just because they’re natural doesn’t mean they’re harmless. And because we have found such countless uses for these metals throughout the ages, today’s children, adults, and wildlife must contend with their effects on health.

Like many other chemicals, lead and mercury exact their most devastating toll on the developing brain. Children exposed to lead at a young age are more likely to suffer from shorter attention spans and are less able to read and learn than their peers (Gilbert 2004). A recent analysis of multiple studies by scientists at the Cincinnati Children’s Hospital found that lead has a significant effect on brain development at blood levels below 10 µg/dL, the current level at which public health agencies take action. In fact, they found no level that did not have an impact on intellect as measured by a decrease in IQ scores (Lanphear 2005).

Research on mercury shows similar effects. Mass poisoning episodes, like that in Japan’s Minamata Bay community in the 1950s, have proven that mercury can cause birth defects including mental retardation and deformed limbs, and studies on children with above-average mercury exposures show that the metal can affect their ability to learn. In a study published in 2005, Harvard Medical School researchers tested mercury in new mothers’ hair at the time of childbirth and found that infants exposed to less mercury in the womb scored better in intellectual tests (Oken 2005). Arsenic may also affect the developing brain: a recent study found that children with greater exposure to arsenic had deficits in intelligence compared to their less-exposed peers (Wasserman 2004).

Lead, mercury, and arsenic do not stop at harming the developing brain. Their health effects have been well-studied, and are summarized in Table 1. It should be noted that many of these effects occur only at relatively high exposure levels.

Table 1:  Common Health Effects of Lead, Mercury, and Arsenic