In my last post, I outlined mercury’s journey from trace amounts in coal to a potent poison in fish. Because coal contains small amounts of mercury, and because we burn coal for energy in large amounts, and because many coal plants have neglected to use readily available pollution control technologies in their smokestacks, mercury accumulates in the aquatic food chain as methylmercury. People eat fish, and methylmercury enters our blood. What happens next?

Methylmercury “affects the immune system, alters genetic and enzyme systems, and damages the nervous system, including coordination and the senses of touch, taste, and sight,” according to the US Geologic Survey. At high levels, methylmercury causes obvious poisoning.

According to the Centers for Disease Control and Prevention (and sorry for the medicalese):

Overt poisoning from methyl mercury primarily affects the central nervous system, causing parasthesias [abnormal skin sensations like tingling, itching, tickling, and burning, from peripheral nerve damage], ataxia [loss of muscular coordination from nervous system damage], dysarthria [difficulty speaking caused by nervous system damage], hearing impairment, and progressive constriction of the visual fields, typically after a latent period of weeks to months. High-level prenatal exposure may result in a constellation of developmental deficits that includes mental retardation, cerebellar ataxia, dysarthria, limb deformities, altered physical growth, sensory impairments, and cerebral palsy.

So — methylmercury poisoning in adults causes a range of nervous system effects. But did you catch the part about prenatal exposure? Methylmercury poisoning in utero causes a different set of problems. Indeed, they are different diseases.

Researchers know this from the autopsies of poisoning victims, which reveal exactly how methylmercury harms the brain. The adult disease shows a specific pattern of damage in the brain: “localized lesions in certain brain areas…along with lesions of peripheral sensory nerve fibers.” In children, methylmercury poisoning causes “more widely distributed damage on the brain.” However, “infants and children who had been poisoned prenatally (from the mother’s diet) showed a diffuse pattern of damage with disruption to normal structures.” (From Grandjean, Satoh et al, 2010).

The complex architecture of the brain is differentially impacted by methylmercury’s damage, depending on a person’s age. In adults, poisoning from this substance causes lack of muscle coordination and unusual skin sensations. In infants, poisoning from this substance causes permanent retardation and limb deformities. Another way of saying this is that the younger you are, the more harmful methylmercury is to your nervous system.

This differential effect is a result of the precisely timed, stunningly complex process of fetal brain development. As described by Phillipe Grandjean and Philip Landrigan:

During the 9 months of prenatal life, the human brain must develop from a strip of cells along the dorsal ectoderm of the fetus into a complex organ consisting of billions of precisely located, highly interconnected, and specialised cells. Optimum brain development requires that neurons move along precise pathways from their points of origin to their assigned locations, that they establish connections with other cells, both nearby and distant, and that they learn to communicate with other cells via such connections. All these processes have to take place within a tightly controlled time frame, in which each developmental stage has to be reached on schedule and in the correct sequence.

This amazing process, when disturbed, causes lifelong and permanent damage. And it renders the fetus more vulnerable to damage from nerve poisons such as methylmercury than adults.

I’ll explore these health effects in a future post. But I can guarantee that you would not want your child to experience them. And that you’d be willing to fight to ensure that she doesn’t.

Here’s something you can do today: join the Moms Clean Air Force to fight for mercury-free babies. We need your voice.