"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.
One in every three of American women have detectable levels of mercury in their blood. (Photo by Kathleen Franklin)
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 nationís 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 Alzheimerís 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 journalís 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.
Copyright Environment News Service, ENS, 2009. All rights reserved.