by Iain Murray
April 7, 2005

Mercury is all over the news these days, which is appropriate for an element named after the messenger of the gods.  At some Maryland high schools, hazmat teams rush in to remove mercury that had gone unnoticed.  In Washington D.C., a broken thermometer causes a school to close.  And across the nation, environmental groups denounce the Environmental Protection Agency’s new proposed rules for reducing mercury emissions from power plants as inadequate to protect children.

All this seems rather odd to those of us who played with mercury in science lessons at school.  The fact is that the health effects of mercury have been dramatically overblown.

First, liquid, elemental mercury—the kind used in science lessons and old-fashioned thermometers—is only very slightly toxic.  Prolonged exposure to large quantities is needed before one starts feeling ill effects.  The incidents are good old-fashioned panics.

Mercury becomes much more dangerous if inhaled or ingested but it becomes really dangerous when it is compounded with other substances.  Yet exposure to such compounds is rare these days.

The most common exposure to dangerous mercury comes from eating fish contaminated with methylmercury.  This is the source of the furor—and confusion—about the EPA rule.  Groups like The Sierra Club say, “high mercury levels [in fish] can cause birth defects and learning disabilities.”  But the evidence for that claim is disputed.  One study from the Faeroe Islands found a link between mothers eating large amounts of fish and learning disabilities in their children (but they might actually be attributable to whale blubber, common in the Faeroe diet)—but a similar study in the Seychelles found no such link.  A third New Zealand study was inconclusive.  As a result, University of Rochester pediatric neurologist Gary Myers has said, “We do not believe that there is presently good scientific evidence that moderate fish consumption is harmful to the fetus.”

The Sierra Club also says that, “five million American women of childbearing age have dangerous levels of mercury in their bodies.” This is a distortion.  The study referred to (published in the Journal of the American Medical Association) found that none of the women in its survey had a blood mercury level above 58 parts per billion, the level at which the EPA believes there is actual risk of health problems.

Now, even taking at face value the claim that power plants are causing neurological impairment by contaminating fish, is there a case for the new rules?  The EPA has come under fire for not including health effects in its cost-benefit analysis.  Thankfully, economists Ted Gayer and Bob Hahn of the AEI-Brookings Joint Center for Regulatory Studies have undertaken just such an analysis.  They found that, “a complete elimination of U.S. power plant emissions would result in a decrease in mean maternal blood mercury levels of 0.13 parts per billion.”  In other words, the measure would have virtually no detectable effect, but at high cost. 

Even if the negligible decrease in blood mercury levels resulted in a $150 million benefit to the nation in terms of slightly increased IQ levels, the measure will still cost billions.  Gayer and Hahn conclude, “As a society, we are in real danger of focusing on de minimis risks if they become salient political issues…We are likely to spend billions of dollars on reducing mercury emissions from power plants and get very modest, if any, improvements in IQ scores in return.”

Mercury is not a serious problem in the United States.  Whatever problems it may bring can be addressed through simple, commonsense solutions.  For instance, women who are pregnant or thinking of becoming pregnant should avoid eating large, long-lived species of fish like shark, swordfish, king mackerel, and tilefish.  Indeed, they will continue to get significant health benefits from eating other fish.  The rest of us can have our canned albacore tuna, high school science lessons, and affordable energy without worry.  Now that’s a message we mere mortals can take to heart.