Your Child’s Brain On Mercury

BY ON August 18, 2011

Baby crawling in puddleThese days, as the EPA is denounced as a job-killer, I often think about a story from the deep, dark, long-ago era of the twentieth century.

Once upon a time, a gleaming, modern chemicals factory fueled Japan’s burgeoning plastics industry, providing jobs and wealth for the Minamata community. The busy factory deposited its untreated, polluted industrial wastewater directly into Minamata Bay, and although fish populations in the bay dwindled, the factory kept expanding, and the wastewater kept flowing. The factory was successful.

Starting in the 1930s, the factory’s wastewater contained increasing concentrations of highly toxic methylmercury, and by the late 1950s, children in Minamata exhibited signs of a central nervous system disease that included difficulty walking, convulsions, and difficulty speaking. Doctors thought at first that it was some kind of unknown contagious disease. But it was not. It was methylmercury poisoning, from the factory wastewater.

Thousands of people were poisoned by methylmercury in Minamata through eating contaminated fish. But one of the saddest details to me as a mom is the fact that mothers gave birth to infants with spasticity, blindness, and profound mental retardation – even when they themselves had shown little if any clinical symptoms of methylmercury poisoning.

The moms looked fine, felt fine, and generally were fine. But their babies were not, because of their special vulnerability to methylmercury damage.

Now flash forward to our enlightened era. Nothing like that could happen today, in America, right?


Today, our power plants spew mercury into the air – especially those plants lacking up-to-date scrubbers and filters. That mercury moves up the marine food chain as methylmercury, and we eat it in fish. But even if your baby was not born with severe clinical symptoms of methylmercury poisoning (now known as Minamata Disease), the mercury in your blood could have harmed your baby. That’s because methylmercury toxicity occurs on a continuum. The higher the dose of methylmercury in your blood, the worse the brain damage in your baby. Conversely, while the low-level effects might be relatively mild, it appears that there are effects even at very low levels of exposure.

What do I mean by “relatively mild”? When the severe clinical symptoms are spasticity, blindness, and profound mental retardation, the mild ones are not walks in the park. Mild symptoms might include delayed language acquisition, impaired verbal memory, and problems with coordination and balance. For example, your preschooler might forget words she’s already mastered, and use fewer words. Or she might become more clumsy and awkward. She might fall down more often, or lose her balance more easily.

I am certain I would notice these frightening symptoms if they developed in my child. But what if she had been exposed to methylmercury in utero? What if she came out more clumsy than other children, or slower at learning learning words than other children? Would it even occur to me that these apparent personality factors were related to an environmental pollutant? I think not. “Every child is different,” I might say, “and develops at her own pace.”

Other cognitive symptoms would be even harder to detect, such as attention deficits and reduced IQ, both of which have been linked to methylmercury exposure. These are health effects that may occur in the absence of other clinical symptoms of mercury poisoning.

Philippe Grandjean and Philip Landrigan summarized the research on the health effects of lower levels of methylmercury in 2006:

Recent studies have focused on prenatal exposures to reduced concentrations of methylmercury. They have examined populations with a high intake of seafood and freshwater fish with various degrees of methylmercury contamination. Prospective examination of a New Zealand cohort noted a three-point decrement in intelligence quotient (IQ) and changes in affect in children born to women with mercury concentrations in hair of greater than 6 μg/g. A large prospective study in the Faroe Islands noted evidence of dose-related impairments in memory, attention, language, and visuospatial perception in exposed children. A third prospective cohort study in the Seychelles provided no support for prenatal neurotoxicity after adjustment for postnatal exposures. Several cross-sectional studies recorded significant associations between methylmercury exposure and neurobehavioral impairment in young children.

These symptoms are non-specific, with so many other factors at play. Can you tell that your child should be functioning at an IQ level three points higher than her current IQ? Can your pediatrician? But try telling me that any aspect of your child’s developing mind is unimportant. Those three points are not murderous; they’re not Minimata; but they are appalling. They are your child’s brain, damaged by mercury, at a juncture of human history when we need all the brain power we can muster.

I can just imagine the moms and dads of the future shaking their heads: “The children looked fine, felt fine, and generally were fine. Except for the small matter of reduced brain capacity.”

JOIN THE MOMS CLEAN AIR FORCE to fight for mercury-free babies.

TOPICS: Mercury Poisoning, Pollution