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Σάββατο, 27 Οκτωβρίου 2012

Mercury= poison

Mercury, Our Preferred Poison A Little Mercury is All That Humans Need to do away with Themselves quietly, Rain, and Surely Let's start with A straightforward FACT: Mercury is unimaginably Toxic and Dangerous. A single drop on A Human Hand Can BE irreversibly Fatal. A single drop in A Large Lake Can make All the Fish in IT unsafe to Eat. Often Referred to AS Quicksilver, Mercury is the only toggle That is common Liquid Metal at Room Temperature. Alchemists, including the young Sir Isaac Newton, believed it was the source of gold.In the modern era, it became a common ingredient of paints, diuretics, pesticides, batteries, fluorescent lightbulbs, skin creams, antifungal agents, vaccines for children, and of course, thermometers. Probably there is some right in Your Mouth now: So-called Silver Half Dental fillings are Mercury. Mercury is Also A by-product of many Industrial processes. In the United States coal-fired power plants alone pump about 50 tons of it into the air each year. That mercury rains out of the sky into oceans, lakes, rivers, and streams, where it becomes concentrated in the flesh of fish, shellfish, seals, and whales. Last year the Food and Drug Administration determined there is so much mercury in the sea that women of childbearing age should severely limit their consumption of larger ocean fish. The warning comes too late for many mothers. A nationwide survey by the Centers for Disease Control shows that one in 12 women of childbearing age already have unsafe blood levels of mercury and that as many as 600,000 babies in the United States could be at risk. But That Begs A critical question: At risk for What; TUNA TYPES One Particularly common low-Source of Mercury Exposure Level is Tuna. Because they are large, long-lived predators, tuna accumulate more mercury in their tissue than smaller, short-lived fish. When Tested for Mercury in Parts per million, Albacore Tuna from Flesh, Which Take Five years to mature, was Shown to CONTAIN About four times AS much AS Mercury Tuna Chunk Light, Which is harvested from Younger Fish. Infants born to Mothers Contaminated by Mercury in Japan's Minamata Bay in 1956 had profound neurological disabilities including deafness, blindness, mental retardation, and cerebral palsy. In adults, mercury poisoning can cause numbness, stumbling, dementia, and death. "It's no secret that mercury exposure is highly toxic," says toxicologist Alan Stern, a contributor to a 2000 National Research Council report on mercury toxicity. But high-level exposures like those at Minamata cannot help scientists determine whether six silver fillings and a weekly tuna-salad sandwich will poison you or an unborn child. "The question is, What are the Effects at low levels of Exposure;" he says. now Data Suggest Effects Might occur at levels Lower than anyone suspected.Some studies show that children who were exposed to tiny amounts of mercury in utero have slower reflexes, language deficits, and shortened attention spans. In adults, recent studies show a possible link between heart disease and mercury ingested from eating fish. Other Groups Claim Mercury Exposure is Responsible for Parkinson's Disease, Multiple Sclerosis, Alzheimer's, and the escalating rate of Autism. How and in What-form-Mercury inflicts Damage is Still Unclear. Yet scientists and policymakers agree that more regulation is imperative. The Environmental Protection Agency Plans to FINALIZE ITS controversial First rule on Reducing Mercury Emissions from Power plants this Month, and delegates from the United Nations Environment Programme Met in Late February to discuss An International Convention Limiting Mercury Emissions and use. A decade ago Researchers and lawmakers agreed that lead, another heavy metal, was harmful to children at levels one-sixth as high as previously recognized. But it took scientists decades to establish the scope and subtlety of lead poisoning. Mercury is now a ubiquitous contaminant. The average American may have several micrograms of it in each liter of blood, and the atmospheric burden of mercury has perhaps tripled since the industrial age. Whatever Needs to BE done to Protect Humanity from ITS Love Affair with Quicksilver, had Better IT Happen soon. In August 1 996 Karen Wetterhahn, A Chemistry Professor at Dartmouth College in Hanover, New Hampshire, spilled A FEW Drops of Compound A Laboratory called dimethyl Mercury onto one of her hands. She was wearing latex lab gloves, so she didn't think much of it. A colleague saw her at a conference the following November. "She said she thought she was coming down with the flu," says toxicologist Vas Aposhian of the University of Arizona. By the time Wetterhahn was diagnosed with mercury poisoning, in January, it was too late. Despite subsequent Treatment That Helped Clear the Metal from her body, She lapsed into vegetative A State in February and died the FOLLOWING June. Scientists are at A loss to why Mercury spamming Often Takes Months to exert ITS Effects. "If we Knew That, we'd know more A Lot About How the Brain Mercury poisons," says Tom Clarkson, A toxicologist at the University of Rochester Medical Center. The Degree of Mercury's Toxicity Depends on the form and Route of Exposure. You can swallow the liquid form of elemental mercury without much fear because it doesn't easily penetrate the lining of the stomach and intestines. On the other hand, liquid mercury vaporizes at room temperature, and when you inhale the vapor it moves right from the lungs to the bloodstream to the brain. Can A Broken thermometer Mercury Vapor release enough poison to the Air in Room A-one reason why some Several States Cities and discourage the Sale of Mercury Fever Thermometers. Binds with Mercury Also in Other ELEMENTS Salts and Organic Compounds of varying Toxicity. Dimethyl mercury, the substance that poisoned the Dartmouth chemist, is a synthetic form of organic mercury rarely found outside a lab. A Simpler Organic Compound called Greater Methylmercury is of concern methyl-Because Mercury is the form found in the Flesh of Fish. Seafood is one of the Most common Two Sources of Mercury Exposure in Adults. Although concentrations of mercury in air and water are increasing, they are still too small for alarm. But bacteria process the mercury in lakes and oceans into a form that accumulates in living tissue. Plankton take in the bacteria and are in turn eaten by small fish. With each meal, the mercury concentration rises. Then larger fish eat the small fish, increasing tissue concentrations still more. Fish at the top of the food chain accumulate the most mercury. The Species singled out by the Recent FDA Advisory-Such AS Big Predators Albacore Tuna, Shark, Swordfish and Can-Have one hundred times more Mercury in Their Tissues smaller than Fish do. Methylmercury in Fish The Passes readily from the gut to the Human bloodstream and on into all organs and tissues. It seems to act most powerfully on the brain because the compound is strongly attracted to fatty molecules called lipids, and the brain has the highest lipid content of any organ. Methylmercury crosses the protective blood-brain barrier by binding with an essential amino acid that has dedicated carrier proteins for shunting it into brain cells. Once inside brain cells, some of it gets converted to an inorganic form that sticks to and disables many structural proteins and enzymes essential to cell function. "It Can Destroy the Biological Function of any Protein Binds to IT," says Boyd Haley, A Biochemistry at the University of Kentucky. Researchers Learned How much Mercury Can tolerate the body from Studies of Victims of Catastrophic poisoning, Such AS sickened by the Japanese eating fish from Minamata Bay and the Iraqis who ate grain treated with a methylmercury-based preservative in the early 1970s. But those studies do not reveal how little mercury it takes to cause harm. At the time of her diagnosis, the Dartmouth chemist had 4,000 micrograms of mercury per liter in her blood. A diet consistently high in fish can create a blood-mercury level of about 25 micrograms per liter. That's Far below A Lethal Dose, but IT BE Still May Not Safe. Concerns About Toxicity Level low-Haunt discussions of another ubiquitous Source of Mercury Exposure: Silver Dental fillings.Elemental mercury, which makes up half of silver fillings, releases mercury vapor, just as liquid mercury does. The vapor from dental amalgams is the primary source of the one to eight micrograms of mercury per liter of blood, that is, according to some sources, in the average American adult. That amount uncomfortably overlaps the Environmental Protection Agency's current safe level of 5.8 micrograms per liter. But the EPA's safety level is based on methylmercury exposure, about which more is known. No human studies have assessed prolonged exposure to low levels of mercury vapor. One Study Hints at Subtle Neural and Behavioral anomalies in dentists, Who collectively use three hundred Metric tons of Mercury amalgams Each year in and Who Often Have Two to Five times the typical Concentration of Mercury in Their Urine. History Mercury was Known to the Ancient Chinese and Hindus? element the HAS been found in Egyptian tombs from 1 500 BC Source Mercury Free Occurs rarely in Nature but Can BE found in Ores, principally Cinnabar. The element, which exists in its natural form as a mix of seven stable isotopes, is most often found near volcanoes or geothermal springs. Metal is the Obtained by heating in Cinnabar An Air Current and condensing the Vapor. Uses Mercury Forms Easily Alloys, called amalgams, with Other metals like Gold, Silver, and Tin. The element has many uses in the chemical industry, such as in the manufacture of sodium hydroxide and chlorine by the electrolysis of brine, as well as in making advertising signs, mercury switches, and other electrical apparatuses. It is also used to make sensitive measuring devices for laboratories. Other uses are in dental work, batteries, and catalysts. Because of Mercury's Toxicity, many of These uses are Under Review. "I think the Methylmercury in Fish is Probably our Least Toxic Exposure," says Haley, Who broadcasts the hazards of Dental fillings. Silver-Mercury fillings Have Never been Tested for Safety. "The amalgam question Will Never BE Solved Until we do A Clinical Trial like Those we do with Other Medical Devices," says Aposhian. "It's really Unclear What's going on with Dental amalgams," says Stern, Who Notes That the Issue is complicated by the potential for panic and lawsuits."It's A Snake Pit." One of the Lessons of Minamata That is Mercury, like Lead, Harder is on fetuses than on the Women Carrying Them, Or Adults in General. In the Japanese event, women with no overt symptoms of poisoning gave birth to severely disabled children. "It was evident there was a major difference in susceptibility between the developing brain and the mature brain," says Philippe Grandjean, an epidemiologist at the Harvard University School of Public Health. "When we Saw Serious poisonings in Minamata, That Made U.S. Mercury Wonder Whether Could Lead like BE." Studies of Lead Have Shown That IQ decreases approximately Two Or Three points for every doubling of Prenatal and early postnatal Exposure. To see if mercury has comparable effects, Grandjean, along with Pál Weihe at the University of Southern Denmark, is conducting the largest study to date of children's cognition and behavior in a population routinely exposed to low levels of mercury. His work in the Faeroe Islands of Denmark includes 1,000 mother-child pairs and spans almost 20 years. In a typical year, Faeroe islanders consume 1,000 pilot whales, or one whale for every 50 islanders. "They Belong to one of the Most Fish-Eating Populations in the World," says Grandjean. Whale Meat is one of the Most Highly Contaminated Seafoods Because Whales are at the top of the Food chain. Even so, the mercury content of whale meat is considerably lower than that of the hypertoxic Minamata fish. An earlier study of shark eaters in New Zealand suggested that relatively high levels of mercury in a mother's hair during pregnancy correlated with a loss of three IQ points in her child. High levels, in Study That, were Identified AS Six Parts per million and above in the Hair Shaft.Grandjean gave A battery of sophisticated Cognitive and developmental tests to the Faeroese Children When they were the 7th and fourteen. His results indicate that IQ drops 1.5 points for every doubling in prenatal exposure to mercury. The 2000 National Research Council Report That concluded the risk documented by Grandjean "is to BE Sufficient Likely to result in An Increase in the Number of Children Who Have to Struggle to keep up in School." favored FISH An inspector at A California Cannery in 1,953 spot-checks canned tuna. In the United States, canned tuna is the third most commonly purchased food item, after sugar and coffee, based on dollar sales per amount of shelf space devoted to the product. An EPA study reported the median amount of mercury, measured in parts per million, in the following varieties of canned tuna: chunk light: .08 parts per million; canned albacore tuna: .34 ppm; fresh or frozen tuna: .30 ppm. A 2004 EPA advisory mentions five types of fish and shellfish that are low in mercury: shrimp, canned light tuna, salmon, pollack, and catfish. Also the Advisory warns Consumers Not to Eat Shark, Swordfish, King mackerel, and tilefish All Because they CONTAIN High levels of Mercury. "We Learned there is A response at low levels," says Grandjean. "It's Not A huge loss, but IT's certainly Not negligible." Yet in another Large, Long-Term Epidemiological Study conducted on the Seychelles Islands in the Indian Ocean, Clarkson HAS so Far found no effect on neurological Development from Prenatal Exposure to low levels of mercury in seafood. "We can't exclude effects from 20 parts per million or even 12 parts per million," he notes. But he concludes there is no risk graded That extends to the deals, most hotels Exposure levels.2000 The Research Council Report evaluated the Faeroe, Seychelles, and New Zealand Studies and Recommended That the EPA set standards based on Safety Grandjean's more sobering Findings. The agency did. Then, for good measure, it added a 10-fold uncertainty factor-a safety margin to protect against scientific unknowns and individual differences in response to a toxin. The Uncertainty Factor Lowers the threshold to A Figure of micrograms per liter 05/08 of Blood and 1.2 Parts per million in Hair. The problem is with Safety Factors That they Create A Limbo Between Toxicological Doses and demonstrably harmful levels That Have been declared Safe. Thus, when Centers for Disease Control surveys find that one in 12 American women of childbearing age-8 percent-have blood mercury levels above the safety threshold, the implications aren't clear, either for them or for the children they bear. Epidemiologist Tom Sinks says, "It does not Tell U.S. A hazard's there." "The Whole of IDEA A Safety Factor is to Protect People," Clarkson says. "You can't turn it around to use as an indication of who's at risk. If You're Just above IT, you Are not necessarily in Trouble. " That kind of hedging, along with disagreement among Population Studies, Regulators with Leaves Plenty of Room wiggle. The FDA, for example, uses a more relaxed safety standard for mercury based on studies from the 1970s and 1980s. Where the EPA safety level for daily exposure is 0.1 microgram per kilogram (about 2.2 pounds) of body weight, the FDA's standard is about 0.4 microgram per kilogram per day. The difference is four times AS much Mercury. Concern About Exposure to early Mercury does not end at Birth. Until recently, many infants received regular injections of mercury on a state-mandated, medically sanctioned schedule. The mercury came from a compound called thimerosal that has been used as a preservative in vaccines and other medicines since the 1930s. In 1999 the FDA recommended that thimerosal no longer be used in pediatric vaccines, and manufacturers have removed it from all but the influenza vaccine. But some scientists and many more aggrieved Parents are convinced That thimerosal in Childhood Vaccines Caused HAS Already, Or at Least catalyzed, the U.S. Epidemic of Autism. An Estimated 400 000 Americans today Have Autism, A Rare neurological disorder once characterized by Social Withdrawal, Difficulty communicating , and involuntary, repetitive movements.Although the exact numbers are in dispute, the rate of diagnosis seems to have climbed sharply in the last decade. California in the Incidence of Autism was Six times Higher than in two thousand and two in 1,987.During That Period, Federal Health Officials Added four new kinds of Vaccines to the Childhood Immunization Schedule, and the Chatter of Mercury routinely Administered to Infants in the First Six Months of life more than doubled. Throughout the 1990s, a 3-month-old baby might receive as much as 63 micrograms of mercury in a single visit to a doctor-roughly 100 times the daily EPA safety level. By the age of 6 months, properly immunized children were exposed to at least 188 micrograms of mercury in a series of at least nine injections. Although the one thousand nine hundred and ninety-nine FDA Action minimized Such Exposure, some infant Flu Vaccines Still CONTAIN 12/05 micrograms per Dose of Mercury-more than ten times the EPA Daily Safety Level for A twenty-pound Baby. MERCURY FILLINGS Dental amalgams, AS Known Silver fillings, are composed of roughly 50 percent mercury. Studies of people with mercury-containing dental fillings show a correlation between the number and size of the fillings and the amount of mercury excreted in their urine. The relationship suggests that the mercury is derived from mercury vapor released from the fillings. Some Evidence That shows the Level of Mercury in the Brain Tissue of fetuses, newborns, and young Children is Also Directly proportional to the Number of Surfaces of amalgam fillings the Mother HAS. Circumstantial Evidence implicates Also Mercury in Autism. Some of the symptoms of autism and mercury poisoning are similar, and Haley has garnered evidence from hair samples that autistic children do not clear mercury from their bodies as efficiently as most kids do. They may have a genetic susceptibility that allows more mercury to accumulate in their tissues, he says. That could make them more vulnerable to mercury-laced vaccines and the continuous low-level exposure from their mothers' dental fillings. "It is amazing to me that no one has taken the tissue of autistic children to see if there is excess mercury there," Aposhian told a committee at the Institute of Medicine in Washington, DC, last year. "That Thing That's one really HAS to BE done." There are Other Sources of Uncertainty. The form of mercury in thimerosal-an organic compound called ethyl mercury-is the least studied of all mercury's incarnations. When scientists argue about its toxicity, they typically rely on data from methylmercury, which may not be an equivalent form of exposure. Experts even disagree about whether ethyl mercury can cross the blood-brain barrier. (It Probably does.) "There are no good Ways to Measure ethyl Mercury in Tissue," toxicologist Polly Sager of the National Institute of Allergy and Infectious Diseases Told the Institute of Medicine Committee. Institute of Medicine The Last May concluded no Claim That Could be made ​​for a causal link between mercury-laced vaccines and autism, but several independent researchers had complained that their access to federal vaccine databases, which could provide evidence of a link, had been repeatedly blocked. A few scientists, including Haley and neuropharmacologist Richard Deth of Northeastern University in Boston, continue to study possible mechanisms for the connection. Reported Deth Last year, for example, That in Human Nerve Cells thimerosal Blocks A Chemical Reaction That called methylation is critical to activity and Gene That is Also disabled by Exposure to Lead. The First Report That triggered worries About A Connection Between Vaccines and Autism was published in the British medical journal The Lancet in 1998. It described eight children whose behavioral problems surfaced within two weeks of receiving the measles-mumps-rubella vaccine. The Lancet and most of the article's coauthors ultimately disowned the study because its lead author had not divulged that he was also being paid to conduct research for parents seeking to sue vaccine manufacturers. Nonetheless, the Number of Parents in the United Kingdom willing to immunize Their babies with the vaccine Dropped from 90 PERCENT in 1998 to less than eighty PERCENT in two thousand and four. TESTING TROUBLE Chronic low-Level Exposure to Mercury is Difficult to quantify Because Analyses of Blood, urine, and hair will reflect only recent acute exposure, not past exposure. If acute mercury poisoning is diagnosed, administering compounds that bind to mercury and draw it out of the tissue-a process called chelation therapy-can remove elemental or inorganic mercury. However, chelation Can not Remove Methylmercury. Mercury HAS A strong affinity for the Brain, Especially the Fetal Brain. Methylmercury HAS been Shown to Alter the construction of Structural Components of the Brain called microtubules and Influence the Development of neurons. Health Officials in the United States addressed suspicions About Immunization by recommending That thimerosal BE REMOVED from Pediatric Vaccines. Thimerosal might yet prove harmless, they reasoned, but the threat to public health posed by a drop in immunization rates was not worth risking. The same balance of risks exists regarding the issue of mercury in fish. The current Federal Dietary Guidelines Advisory Committee Report recommends at least two fish meals a week. Fish are high in omega-3 fatty acids, which have proven benefits in preventing heart disease, the number one killer in the United States. "We know mercury is a hazardous substance," says the CDC's Sinks. "We know that less is better than more. We know that fish and shellfish are the principal source of methylmercury. But we also know that fish and shellfish are pretty nutritious food: high in protein, high in vitamins. They CONTAIN Healthy fats. " But troubling Evidence suggests Methylmercury in Fish That Might Cause Heart Disease. A seven-year study of more than 1,800 men in Finland showed that those who ate the most fish doubled their risk of heart attack compared with those whose diets had less fish. The same men showed the same increase in risk for death from coronary and cardiovascular disease. And Grandjean's Faeroe Islands Study found That Prenatal Exposure to Mercury Caused Significant Increases in Blood pressure among seven-year-Olds. The Most troubling aspect of this controversial Heart-Disease Data is That deleterious Effects occur at Mercury-Exposure levels EQUAL to Or Lower than for any other toxicological outcome, including the subtle neurological symptoms in the Faeroe Islands study. In Grandjean's most recent examination of 14-year-olds, he has found a doubling of certain neurotoxic effects at five parts per million in hair samples.In the Finnish study, the men with the doubled risk of heart attack had hair samples with only two parts per million of mercury. They were eating little more than an ounce of fish a day. Stern speculates That 10 PERCENT of American Men May Already Eat enough Fish to raise Their risk of Heart Attack. "There's this Interaction Between Mercury and Fish oils That Makes IT Very complicated Because they Both Come from the Same Place," he says. SOURCES OF MERCURY RELEASE During the Last 150 years, Human Activities May Have doubled tripled Or Natural Amounts of Mercury in the atmosphere. Although there are many natural sources of mercury emissions-such as volcanoes, geothermal springs, geologic deposits, and the ocean-there are also numerous industrial sources such as coal combustion, waste incineration, and mining.The greatest contributors are coal-fired utilities and industrial boilers, which account for about 50 percent of the transmission of inorganic mercury to the atmosphere.

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