Have you ever wondered why environmentalists are so concerned about the way we dispose of even trace amounts of mercury, such as that contained in your fever thermometers, thermostats, and compact fluorescence lightbulbs (CFLs)? The answer comes from a hard lesson we learned over a half century ago involving an environmental disaster at a place called Minamata Bay, Japan.
Starting in the 1940s and continuing through 1968, a chemical plant in Minamata Bay released the industrial effluent containing mercuric compounds into the river and bay. These mercuric compounds were slowly bio-transformed by aquatic microorganisms into methylmercury, a more toxic chemical which accumulated in the bay’s marine life. People eating fish caught in the bay experienced a wide variety of devastating toxic effects.
Patients experienced neurologic damage, ranging from tremor, sweating, neuropathies, visual disturbances, hearing loss, seizures, psychological disorders, and death. An even more unfortunate consequence of exposure was its toxicity to unborn fetuses and children of young age. In this population, neurologic damage was typically more severe, including many cases of mental retardation. During this time 121 deaths were officially linked to methylmercury ingestion; however thousands more are believed to have been sickened by this condition which is now termed “Minamata Disease”.
Mercury is a heavy metal that is found within the earth’s crust and can be widely dispersed throughout the air, soil, water, plants and animals. Mercury exists in several forms. Elemental or metallic mercury is the silvery-gray liquid metal that you would find in thermometers or blood pressure gauges. Toxicity from this source is primarily from chronic inhalation of its vapors.
So, why is methylmercury so scary? Methylmercury, (also called organic mercury), easily enters the brain and nervous system. Dumping or improper disposal of any form of mercury into water systems results in conversion to methylmercury, which accumulates as a toxin in seafood. Excess consumption of contaminated fish by humans (see list below), especially children and pregnant women, can put you at greater risk of toxicity from methylmercury. Such as was the case of Minamata Bay.
How does this affect you in 2012? Thousands of rivers and lakes worldwide have been polluted by methylmercury. In January of 2001, the U.S. Environmental Protection Agency (EPA) published ambient water quality criteria (AWQC) recommendations for methylmercury for the protection of people who eat fish and shellfish. The limit is set at 0.3 milligram methylmercury per kilogram fish tissue wet weight. Regulation of this level is ensured through state-supervised random sampling of mercury content in fish.
The U.S. Food and Drug Administration (FDA), in conjunction with the EPA, have issued an advisory on mercury in fish and shellfish for women who may become pregnant, pregnant women, nursing mothers, and young children. The recommendations are as follows:
- Avoid fish that contain high levels of methylmercury
- King mackerel
- Consume no more than 12 ounces (2 average meals) a week of fish with lower methylmercury content:
- Canned tuna
- Albacore tuna has more mercury content than canned tuna, so only 6 ounces are recommended per week
- When catching fish for food, local advisories should be consulted to ask about mercury content of local bodies of water. If no advice is available, only 6 ounces of fish and shellfish per week should be consumed.
If you have any questions or experience an incident involving mercury spillage, clean-up or exposure, please call the Illinois Poison Center at 1-800-222-1222.