While researching my blog series on mercury, I kept reading about “mixed results” of epidemiological research on mercury, with the implication that we can’t be sure whether methylmercury exposure from eating fish is harming children. I decided to get to the bottom of this and some other questions by talking with Philip Landrigan, a pediatrician and Dean of Global Health at Mount Sinai School of Medicine in New York, where he also directs the Children’s Environmental Health Center. Dr. Landrigan is an expert on children’s environmental health, and has written extensively about the health effects of exposure to mercury, lead, and other chemicals in the environment. (Full disclosure: back in the era of my personal history that I refer to as B.C. — Before Children — as luck would have it, I had the great privilege of working for Dr. Landrigan.) An excerpt of our conversation follows.
Interview With Dr. Philip Landigan:
What do you make of epidemiological studies that show no neurological impact of methylmercury exposures?
I’ll put it a different way. The best of the epidemiologic studies have shown an impact. There have been three epidemiologic studies. There was Philippe Grandjean’s study in the Faroe Islands, there was Tord Kjellstrom’s study in New Zealand, and thirdly there’s the study that was done in the Seychelles by the group from the University of Rochester. Of those studies, the Faroes study, has clearly shown an effect. The New Zealand study also shows a clear effect. And the Seychelles study, which has long been touted as a negative study, actually shows some evidence of an effect when you dig down into the data. When the National Academy of Sciences reviewed this issue in 2000, they made the determination that the benchmark study that people should use is the Faroe Islands study. They consider it to be the best one.
Can you talk about the health impacts of methylmercury aside from its effects on the brain?
There’s suspicion that it interferes with cardiac function, possibly by interfering with the cells in the heart that are involved in regulating cardiac rhythm. There have been published studies that show that people who are exposed to mercury have elevated rates of heart disease.
Talk about your concept of “subclinical toxicity.” What does this mean in the case of methylmercury exposure?
Subclinical toxicity is defined as toxicity that is not immediately evident when the child walks into the doctor’s office. It’s toxicity that is discovered not by the standard clinical examination but rather by special testing such as IQ testing or by testing of the child’s reaction time or other tests to get at function in the child. The most sophisticated view of neurotoxicity these days is that there’s a spectrum of toxicity related to the dose, so that at the highest dose levels, methylmercury can cause acute, obvious, devastating neurotoxicity, as was seen in Minamata, Japan, back in the 1950s and 60s, but at lower levels of exposure, too low to produce those sorts of obvious symptoms, methylmercury still causes loss of intelligence and various behavioral alterations in children that can be detected when you put the child through special testing.
How pervasive do you think this is?
I use the data from the CDC on the numbers of children who have detectable levels of methylmercury in their blood to try to get a handle on that. If you go to the paper that we published in Environmental Health Perspectives a few years ago, we used the CDC data as a starting point. Then, knowing the distribution of mercury levels in pregnant women in the country at that time, we figured up to 15% of the children born in this country are at risk of some degree of subclinical impairment as a consequence of prenatal exposure.
What should parents do with this information?
The single most important thing that parents should do is modify their diet. We know that the predominant source of methylmercury is contaminated fish. We also know that not all fish are created equal. Some fish have higher mercury levels and other fish have much lower levels. We know that it’s important for women to eat fish during pregnancy because the Omega-3 fatty acids in the fish are beneficial to brain development in the child. So what women have to do, and it’s our responsibility in the medical profession to educate them about this, women have to learn to eat the right fish during pregnancy. They should be eating fish a couple times a week, but they should be eating fish like sardines, like tilapia, like clams and mussels, that are low on the marine food chain and not fish like shark or tuna, which are high on the food chain. There are many lists out there. I think one of the best is the list that the Monterey Aquarium puts out.
Women who are thinking about becoming pregnant should start watching what species they eat three to six months before they conceive a pregnancy.
Is that the amount it takes to clear mercury from the body?
How about with our children? What should we be doing?
Again, I think fish is good for kids, and children are more resistant to mercury than the fetus, and so I don’t take quite such a hard line thinking about children as I do thinking about fetuses. But I think it makes sense for kids not to gorge on tuna sushi, which we know has lots of mercury in it.
How can people bring this science about methylmercury to our decisionmakers?
At this point, parents have to switch into citizen mode, because the electric power generating industry is obviously a very powerful industry, no pun intended. They are deeply invested in burning coal; and the only way that the problem can be controlled is for people to vote, to write their elected officials, to do all the things that one must do in a democracy to bring about change.