LOS ANGELES, California, September 1, 2009 (ENS) – The level of inorganic mercury in the blood of American women has been increasing since 1999 and it is now found in the blood of one in three women, according to a new analysis of government data for more than 6,000 American women.
“My study found compelling evidence that inorganic mercury deposition within the human body is a cumulative process, increasing with age and overall in the population over time,” said author Dan Laks, a neuroscience researcher at the David Geffen School of Medicine at the University of California, Los Angeles.
In a separate statistical analysis, he found that older women had more inorganic mercury in their blood than younger women, indicating that mercury accumulates in the blood over time.
“My findings also suggest a rise in risks for disease associated with mercury over time,” Laks said.
Laks conducted computer analyses of data from the Centers for Disease Control and Prevention in Atlanta. The CDC’s National Health and Nutrition Examination Survey, usually called NHANES, is what Laks calls the “gold standard” in assessing the health status and health risks to a representative group of Americans. NHANES is unique in that it combines interviews and physical examinations.
NHANES data also are designed and survey weighted so that results can be generalized to the nation’s entire population.
Laks examined data on blood inorganic mercury levels of 6,168 women, ages 18-49, in NHANES two year data sets from 1999 through 2006. Between 1,455 and 1,622 women were in each two-year matched group.
“The overall population average of blood inorganic mercury concentration also increased significantly from 1999-2006,” Laks wrote.
Inorganic mercury was detected in the blood of 30 percent of women studied in 2005-2006, a steep rise from the two percent of women who were found to have inorganic mercury in their blood in the 1999-2000 study.
Blood mercury concentration is widely considered the appropriate indicator of absorbed dose that corresponds to deposition within the human body, Laks explains in the study.
While people face chronic exposure from both the organic mercury form, due to consumption of fish, and the elemental form, due to inhalation from air, and dental amalgams, there is strong evidence that inorganic mercury concentration in the blood is the best bioindicator of chronic exposure to both organic and elemental mercury forms.
Organic mercury is a poor indicator of exposure as it remains in the body for just a few months, Laks explains.
Laks says his analysis indicates associations of “both blood inorganic mercury detection and average concentration with biomarkers for the main organs and systems which mercury targets: the liver, the immune system, and the pituitary gland.”
His study cites numerous other research that has found chronic mercury exposure associated with elevated risks for autism, mental impairment and neurodegenerative disorders such as Alzheimer’s disease.
An earlier analysis of NHANES data by researchers with the U.S. EPA estimated that, as a result of chronic mercury exposure, between 300,000 and 600,000 American children were born with elevated risks of neurodevelopmental disorders between 1999 and 2000.
“These results suggest that chronic mercury exposure has reached a critical level where inorganic mercury deposition within the human body is accumulating over time,” said Laks. “It is logical to assume that the risks of associated neurodevelopmental and neurodegenerative diseases will rise as well.”
One of the journal’s peer reviewers commented, “This is a highly important contribution as there are very few publications that have enough subjects to evaluate accurately the effects of increased body levels of mercury on biomedical parameters in humans.”
The study is published online in “Biometals,” an international peer-reviewed journal on the role of metal ions in biology, biochemistry and medicine, and will appear in a future print edition of the journal.
Student spills mercury at Denver’s Lincoln High
A student at Denver’s Lincoln High School brought mercury to school Wednesday, and had to be decontaminated by firefighters.
The incident happened around the lunch hour when the student spilled a trace amount inside the school, said Lt. Phil Champagne, a Denver Fire Department spokesman.
The Fire Department’s hazardous- materials unit cleaned up a minuscule amount of mercury from a classroom, Champagne said.
In August 1996 Karen Wetterhahn, a chemistry professor at Dartmouth College in Hanover, New Hampshire, spilled a few drops of a laboratory compound 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 a vegetative state in February and died the following June.
Scientists are at a loss to explain why mercury often takes months to exert its effects. “If we knew that, we’d know a lot more about how mercury poisons the brain,” 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. A broken thermometer can release enough mercury vapor to poison the air in a room—one reason why some cities and several states discourage the sale of mercury fever thermometers.
Mercury also binds with other elements in 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 methylmercury is of greater concern because methyl- mercury is the form found in the flesh of fish.
Seafood is one of the two most common 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—big predators such as albacore tuna, shark, and swordfish—can have 100 times more mercury in their tissues than smaller fish do.
The methylmercury in fish passes readily from the human gut to the 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 it binds to,” says Boyd Haley, a biochemist at the University of Kentucky.
Mercury was known to the ancient Chinese and Hindus; the element has been found in Egyptian tombs from 1500 B.C.
Mercury rarely occurs free 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. The metal is obtained by heating cinnabar in an air current and condensing the vapor.
Mercury easily forms 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 is that mercury, like lead, is harder 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 us wonder whether mercury could be like lead.”