Why is Mercury a Problem?

In lakes and rivers, mercury from dental amalgam is transformed from its elemental form into methylmercury by bacteria living in the water column and in the sediment. Methylmercury is persistent in the environment. It also bioaccumulates through the food chain. Fish-eating birds like eagles and osprey have been found to have high levels of mercury in their brains causing them to reproduce less successfully than normal and hindering their speed and coordination, affecting their ability to catch prey and avoid predators.

And of course, when humans eat fish the mercury in them enters our body. Mercury contamination is the number one reason why we can't eat many of the fish caught in our lakes and rivers. 96% of all government fish consumption advisories in Canadian waters are a result of mercury contamination of fish tissues. It takes just 1/70 of a teaspoon of mercury to make all of the fish in a 25 acre lake unsafe to eat.

Mercury also has direct impacts on humans who are exposed to it. Methylmercury is a neurotoxin in low doses, affecting the functioning and development of the nervous system. Methylmercury is rapidly absorbed through the gastrointestinal tract and readily crosses the blood brain barrier into the adult or fetal brain.

Depending on the level of exposure, this toxin can have varied health effects ranging from mental retardation to death. Pregnant women need to be especially concerned about mercury contamination because direct exposure to the developing fetus through the mother's placenta could cause various health effects. The U.S. National Academy of Sciences estimates that 60,000 kids are born each year in the U.S. with higher risk of neurological damage due to their mother's fish consumption during pregnancy.

Several incidents of human exposure have confirmed mercury's link to human health problems. In 1972, 6,500 Iraqi adults and children developed neurological problems and 459 people died after they ate grain coated with a fungicide containing methylmercury. In Minimata, Japan, 700 people died, 9,000 people experienced varying degrees of paralysis and brain damage, and 50,000 people experienced at least mild symptoms after being exposed to methylmercury in seafood they consumed.

Airborne mercury is also a considerable threat through inhalation or bodily contact. Exposure can lead to weakness, blurred vision and varying degrees of neurological damage.