Question: There was a warning about eating tuna and some other fish because of mercury. Where does this mercury come from? Is someone polluting the oceans? (Asked by a curious mermaid.)

Reply: Health officials in the U.S. and Europe have announced that pregnant women, nursing mothers and young children should go easy on the tuna (along with shark, swordfish, king mackerel and tilefish) because of relatively high concentrations of mercury. Practically all fish have a bit of mercury in their flesh and fat, but tuna (probably America’s most consumed fish) now carries a warning.

Humans and nature are the culprits. An estimated 50 tons of mercury vapor goes into the atmosphere from coal-fired power plants each year. Nature helps out with mercury vapor coming from volcanoes and hot springs. Much of this vapor is washed out of the air by rain, which pours into the streams and rivers that flow to the sea. In the process, bacteria convert the mercury into methyl mercury — an organic and more toxic form — which is readily absorbed by plants and small creatures.

Little fish eat these, big fish eat little fish, and so on, until you get to your biggest fish — and tuna are some of the biggest! A large yellowfin tuna can measure up to seven feet in length and weigh 400 pounds. A bluefin tuna can be 15 feet in length and weigh 1,500 pounds. Big fish eat more than smaller fish, so the methyl mercury builds up, eventually leaving a large concentration in the fish’s flesh.

So what’s the problem? There are quite a few. Mercury can affect the central nervous system. You start acting a little weird at first, but you can ultimately lose your motor control — and worse.

It is speculated the Mad Hatter in “Alice in Wonderland” had mercury poisoning. Tall beaver skin hats were once popular and a mercury compound was used to treat the beaver pelts. Employees of the hatting industry often acted a bit crazy or mad (a symptom of mercury poisoning), hence the phrase “mad as a hatter.”

C.P.S. (Curious Postscript): “By the time a man is wise enough to watch his step, he’s too old to go anywhere.”

Curious about something? Send your questions to Dr. Jerry D. Wilson, College of Science and Mathematics, Lander University, Greenwood, SC 29649, or e-mail jerry@curiosity-corner.net. Selected questions will appear in the Curiosity Corner. For Curiosity Corner background, go to curiosity-corner.net.