A couple of weeks ago, I read Ayelet Waldman’s post at Mom’s Clean Air Force about how she inadvertently poisoned her 4-year-old daughter with tuna sandwiches and sushi. A terrible story, for sure. A surprising one, too — apparently not everyone is getting the message about mercury in fish.
A child weighing 20 lbs can safely eat a maximum of 1 can of white albacore tuna every 10 weeks.
I’ve looked to a number of environmental and health organizations for information on mercury levels in fish. I think the NRDC’s site is the best. Among a lot of interesting information is a very clear list that groups fish according to how often we can safely eat them. My family sticks to “Least Mercury: Enjoy these fish.” We no longer eat anything under “Highest Mercury: Avoid eating.”
Click on their “Mercury in Fish Wallet Card” for a portable list and a guide to how much canned tuna is safe for a person based on his or her weight.
What does mercury do to us?
Once in the human body, mercury acts as a neurotoxin, interfering with the brain and nervous system.
Exposure to mercury can be particularly hazardous for pregnant women and small children. During the first several years of life, a child’s brain is still developing and rapidly absorbing nutrients. Prenatal and infant mercury exposure can cause mental retardation, cerebral palsy, deafness and blindness. Even in low doses, mercury may affect a child’s development, delaying walking and talking, shortening attention span and causing learning disabilities.
In adults, mercury poisoning can adversely affect fertility and blood pressure regulation and can cause memory loss, tremors, vision loss and numbness of the fingers and toes. A growing body of evidence suggests that exposure to mercury may also lead to heart disease. (link)
The Link to Air Pollution
While mercury is a naturally occurring at low levels, elevated levels in our fish supply are traced to man-made sources.
Coal burning power plants are the largest source of mercury emissions. Chlor-alkali plants use (and lose) mercury to convert salt to chlorine gas and lye, which is used in soaps, detergents, plastics, and paper-making. Cement plants, the fourth largest mercury emitter, burn coal to fire their kilns. The scrapping and melting of automobiles also releases mercury.
These emissions rain down into our lakes, rivers, and streams.
Fish absorb mercury from their food and from water as it passes over their gills. It binds to proteins in fish tissue and cannot be reduced.
Mercury is bio-accumulative. It moves up the food chain, from plankton, to juvenile fish, to large predatory fish. The older and bigger the fish, the higher the concentration of mercury.