Mercury toxicity gets short shrift

THE JAPAN TIMES
Sunday, May 23, 2010

READERS IN COUNCIL


By CHISA HIDAKA, M.D.
New York

Regarding the May 10 article "Most Taiji residents rest easy, refuse to change diet." I am dismayed that the Japanese media's coverage of mercury levels detected in the citizens of Taiji (Wakayama Prefecture) has not included several important points about mercury testing and the effects of toxicity, particularly for women and children.

First, the effects of mercury toxicity are most apparent and most devastating in the pre- and perinatal period — when the nervous system is still developing. Certainly, this was the case in the Minamata cases of the 1950s. A 2007 study comparing levels of maternal-hair mercury and infant IQ in New Zealand and the Faroe Islands showed that every part per million of mercury correlated with a decrease of 0.18 point in IQ. The levels of mercury reported in the hair of Taiji women are four times Japan's national average.

Children should be tested systematically. More important, women should be warned that if they are pregnant or plan to get pregnant, they should have the level of mercury in their bodies tested. Mercury exists in breast milk at about half the level it does in the blood. So, it would be wise for any nursing mothers to have their blood levels tested as well.

Another point that should be mentioned is that mercury levels in hair are used to measure the disease burden in populations, not individuals. The World Health Organization recommends testing the hair of women only; in this regard, though, mercury levels are not a good predictor of anything besides infant IQ. If people want an accurate measure of their personal level of risk and exposure, they should have the mercury levels in their blood tested.

Effects of mercury toxicity in adults are subtle and may not become severe for a long time, particularly if exposure is gradual. On the other hand, effects of prenatal exposure can be devastating and occur at much lower levels than those that lead to problems for adults. As a service to its citizens, newspapers reporting this story should warn the women of Taiji that those of childbearing age should be very concerned about the recent findings.

The opinions expressed in this letter to the editor are the writer's own and do not necessarily reflect the policies of The Japan Times.