Honolulu Star-Advertiser © Susan Scott
February 9, 2008
Mercury is a hot topic in the news lately. This toxic metal is being found in large amounts in some food fish, and recently in dolphins eaten by the Japanese.
The question arises, Should we stop eating these marine animals?
No, says the fishing industry, which has sponsored studies on the subject. The health benefits of eating these fish outweigh the risk of mercury poisoning.
Other researchers say yes, we should stop or cut way back on eating tuna, billfish and shark. Mercury levels are far over the safety limits.
The FDA and EPA stand in the middle. These agencies have issued warnings saying certain people should eat only a certain amount of certain fish at certain times.
Clear on all this? Few of us are.
Mercury is an unusual metal. It’s the only one that’s liquid at room temperature. It has low freezing and high boiling points, useful in thermometers. When heated to boiling, it’s a colorless, odorless gas.
This natural metal gets into the air from volcanoes and other earthly gas passing. Rain and runoff deliver mercury to the water, where bacteria change it into a form plankton can easily absorb. And up the food chain it goes.
Mercury has always been found in minute amounts in nearly all marine animals. But even though it’s natural, mercury is not an essential metal to any species. It’s strictly a toxin.
In tiny amounts mercury does no harm, but eating too much too quickly causes it to accumulate. It takes, on average, 50 days for half the mercury we’ve eaten to be excreted, mostly in the feces, another 50 days for half the rest and so on. This is called the biologic half-life of mercury.
This means if we don’t give our bodies time to get rid of ingested mercury, our blood levels will increase. The amount of mercury people can tolerate before having symptoms varies, but once signs appear it’s too late. Mercury poisoning causes irreversible nerve and brain damage.
In the past, people welcomed mercury, also called quicksilver, into their bodies, using it for things from makeup to medicine (remember Mercurochrome?) The Romans used it in cosmetics, the Greeks in ointments. For centuries, physicians treated syphilis with mercury, likely killing people in the process.
Today we use mercury for a lot of things besides thermometers: mercury-vapor lamps, pesticides, chlorine production, electrodes, batteries, catalysts and more.
Excess mercury gets into the air when these products are thrown out and burned. That, however, is a minuscule amount compared with burning coal, which contains mercury.
More mercury gets airborne from the world’s coal-burning furnaces than from all other sources combined. And that’s why the world’s large carnivorous fish are getting too much mercury in their systems.
So, should we eat fish that test high in mercury?
Since giving it up, or even cutting down, is more of a sacrifice for some people that others, it’s an individual call. But the subject is too serious to shrug off, especially among children and pregnant women. Mercury is particularly lethal to developing nerves.
Type the words mercury and fish into your search engine, like I did, read the pros and cons, and then decide for yourself.
As for me, I’m going to miss my tuna salad sandwiches.