Mercury, also known as quicksilver, is the only common metal which is liquid at ordinary temperatures. Metallic mercury is used in a variety of household products, such as barometers, thermometers and fluorescent light bulbs. Alkali and metal processing, coal-burning power plants, medical and other waste, and mining of gold and mercury contribute greatly to mercury concentrations in some areas. However, the dominant source of mercury over most of the landscape is when mercury enters the atmosphere. Once in the atmosphere, mercury is widely disseminated and can circulate for years, accounting for its wide-spread distribution.
Mercury is a neurotoxin. The “mad hatters” of the 19th century suffered from mercury poisoning which caused personality changes, nervousness, trembling, and even dementia. The hatters were exposed to mercury in the felting process when mercury was rubbed onto cloth to preserve it.
According to the Environmental Protection Agency (EPA), “for fetuses, infants, and children, the primary health effect of methylmercury is impaired neurological development. Methylmercury exposure in the womb, which can result from a mother's consumption of fish and shellfish that contain methylmercury, can adversely affect a baby's growing brain and nervous system. Impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methylmercury in the womb.”
According to a recent article in USA Today, the EPA states that as many as 600,000 babies may be born in the USA each year with permanent brain damage because pregnant mothers ate mercury-contaminated fish.
In 2005, about 500 coal-burning power plants emitted 48.3 tons of mercury, an increase of 1% since 2000, according to a USA Today analysis of the EPA's Toxics Release Inventory. These plants supply half of the nation’s electricity and are the nation’s largest source of mercury air emissions.
Gold jewelry is also extremely profitable amounting to over $44 billion dollars in 2006 making gold jewelry one of the world’s largest categories of consumer goods. An estimated 10 to 15 million small-scale miners rely on mercury to separate grains of gold from small bits of sand and rock using pans or other small scale equipment. The technique results in a gold-mercury amalgam which is later heated to release the mercury and extract the gold.
The largely unregulated flow of mercury is polluting waterways, land, and the miners themselves throughout Africa, South America, and Asia. Because the miners heat the gold-mercury amalgam in open pans elemental mercury is released into the atmosphere. United Nations Environment Program, or UNEP, estimates that “small-scale gold mining releases between 650 and 1,000 metric tons of mercury per year,” and that this pollution accounts for “about a third of all mercury releases to the environment from human activities.”
Once in the atmosphere mercury eventually falls in rain or snow to the ground or water. Rain and melting snow wash mercury into lakes and streams and eventually into the oceans. Bacteria in the soil sediment and water as well as plants convert mercury into methyl mercury. This form of mercury can readily be absorbed into and remain in fish tissue. Fish accumulate methyl mercury into their bodies by eating plants or by direct contact with bacteria.
As ever-bigger fish eat small ones, methyl mercury accumulates in their bodies. The larger the fish the greater the concentration of mercury. Fish such as tuna, swordfish, and shark have some of the highest concentrations. Methyl mercury levels can be 1 million times higher than in the surrounding water.
A letter published in Medical Journal of Australia report on three infants whose parents had sought medical advice for either developmental delay or neurological symptoms in their children. All three children had eaten fish congee, a rice and fish porridge, as a weaning food and ate fish regularly as toddlers.
In the first reported case a 2-year-old boy had demonstrated increasingly “aggressive behavior for the past 6 months.” A general practitioner had diagnosed the boy’s father with mercury poisoning 2 months earlier following complaints of allergies, rashes, abdominal pain, and diarrhea. The boy’s blood mercury level was measured at 158 nmol/L [nanomoles per liter]. The normal range for adults is considered less than 50 nmol/L.
In the second reported case a boy aged 2 years and 10 months presented with “delayed speech and some autistic features.” Since weaning, the boy had eaten fish up to eight times a week. The child’s blood mercury level was 350 nmol/L. Two weeks after removing fish from the diet the child’s blood mercury level had fallen to 99 nmol/L. “However, his behavior did not improve, and he was subsequently diagnosed with classical autism.”
In the final reported case a 15-month-old boy was examined with delayed development since birth. Fish had been introduced to his diet at 8 months of age and had consumed fish four to five times a week. The boys’ mother had consumed fish three to four times a week after the fifth month of her pregnancy. The boy’s blood mercury level was 143 nmol/L, but feel to 19 nmol/L over a period of a year after ceasing fish intake. “His longer-term development status is unknown.”
The authors conclude with a recommendation that “multilingual information about fish and mercury be made available to pregnant women and mothers, especially targeting groups who are likely to be frequent consumers of fish and who use fish in weaning and infant foods. Regulatory and health promotion activities could also be informed by surveillance of blood or hair mercury levels in infants from ethnic groups at high risk of mercury intoxication, and of the frequency of fish consumption in this age group.”
Source: Medical Journal of Australia, 2008