Measuring mercury: Common test may overestimate exposure from dental amalgam fillings
A common test used to determine mercury exposure from dental amalgam fillings may significantly overestimate the amount of the toxic metal released from fillings, according to University of Michigan researchers.
Scientists agree that dental amalgam fillings slowly release mercury vapor into the mouth. But both the amount of mercury released and the question of whether this exposure presents a significant health risk remain controversial.
Public health studies often make the assumption that mercury in urine (which is composed mostly of inorganic mercury) can be used to estimate exposure to mercury vapor from amalgam fillings. These same studies often use mercury in hair (which is composed mostly of organic mercury) to estimate exposure to organic mercury from a person's diet.
But a U-M study that measured mercury isotopes in the hair and urine from 12 Michigan dentists found that their urine contained a mix of mercury from two sources: the consumption of fish containing organic mercury and inorganic mercury vapor from the dentists' own amalgam fillings.
"These results challenge the common assumption that mercury in urine is entirely derived from inhaled mercury vapor," said Laura Sherman, a postdoctoral research fellow in the Department of Earth and Environmental Sciences and lead author of a paper in the journal Environmental Science & Technology. A final version of the paper was published online March 20.
"These data suggest that in populations that eat fish but lack occupational exposure to mercury vapor, mercury concentrations in urine may overestimate exposure to mercury vapor from dental amalgams. This is an important consideration for studies seeking to determine the health risks of mercury vapor inhalation from dental amalgams," said U-M biogeochemist Joel D. Blum, a co-author of the paper and a professor in the Department of Earth and Environmental Sciences.
The study by Sherman, Blum and their colleagues demonstrates that mercury isotopes can be used to more accurately assess human exposure to the metal—and the related health risks—than traditional measurements of mercury concentrations in hair and urine samples. Specifically, isotopes provide a novel chemical tracer that can be used to "fingerprint" both organic mercury from fish and inorganic mercury vapor from dental amalgams.
Mercury is a naturally occurring element, but more than 2,000 tons are emitted into the atmosphere each year from human-generated sources such as coal-fired power plants, small-scale gold-mining operations, metals and cement production, incineration and caustic soda production.
This mercury is deposited onto land and into water, where micro-organisms convert some of it to methylmercury, a highly toxic organic form that builds up in fish and the animals that eat them, including humans. Effects on humans include damage to the central nervous system, heart and immune system. The developing brains of fetuses and young children are especially vulnerable.
Inorganic mercury can also cause central nervous system and kidney damage. Exposure to inorganic mercury occurs primarily through the inhalation of elemental mercury vapor. Industrial workers and gold miners can be at risk, as well as dentists who install mercury amalgam fillings—though dentists have increasingly switched to resin-based composite fillings and restorations in recent years.
About 80 percent of inhaled mercury vapor is absorbed into the bloodstream in the lungs and transported to the kidneys, where it is excreted in urine. Because the mercury found in urine is almost entirely inorganic, total mercury concentrations in urine are commonly used as an indicator, or biomarker, for exposure to inorganic mercury from dental amalgams.
But the study by Sherman, Blum and their colleagues suggests that urine contains a mix of inorganic mercury from dental amalgams and methylmercury from fish that undergoes a type of chemical breakdown in the body called demethylation. The demethylated mercury from fish contributes significantly to the amount of inorganic mercury in the urine.
The U-M scientists relied on a natural phenomenon called isotopic fractionation to distinguish between the two types of mercury. All atoms of a particular element contain the same number of protons in their nuclei. However, a given element can have various forms, known as isotopes, each with a different number of neutrons in it nucleus.
Mercury has seven stable (nonradioactive) isotopes. During isotopic fractionation, different mercury isotopes react to form new compounds at slightly different rates. The U-M researchers relied on a type of isotopic fractionation called mass-independent fractionation to obtain the chemical fingerprints that enabled them to distinguish between exposure to methylmercury from fish and mercury vapor from dental amalgam fillings.
More information: www.lsa.umich.edu/… ld_ci.detail
Journal reference: Environmental Science & Technology
Provided by University of Michigan
- Older dental fillings contain form of mercury unlikely to be toxic Dec 09, 2009 | not rated yet | 0
- Form of Mercury in Older Dental Fillings Unlikely to be Toxic: Study Nov 11, 2009 | not rated yet | 0
- Study shows mercury levels from products decreasing, though still at dangerous levels May 06, 2008 | not rated yet | 0
- Researchers use fluorescence to develop method for detecting mercury in fish Nov 18, 2008 | not rated yet | 0
- Amalgam fillings are safe, but skeptics still claim controversy, researcher says Apr 02, 2009 | not rated yet | 0
- Motion perception revisited: High Phi effect challenges established motion perception assumptions Apr 23, 2013 | 3 / 5 (2) | 2
- Anything you can do I can do better: Neuromolecular foundations of the superiority illusion (Update) Apr 02, 2013 | 4.5 / 5 (11) | 5
- The visual system as economist: Neural resource allocation in visual adaptation Mar 30, 2013 | 5 / 5 (2) | 9
- Separate lives: Neuronal and organismal lifespans decoupled Mar 27, 2013 | 4.9 / 5 (8) | 0
- Sizing things up: The evolutionary neurobiology of scale invariance Feb 28, 2013 | 4.8 / 5 (10) | 14
Assumptions of Griffith's fracture theory
2 hours ago Any experts on Griffith's fracture theory? I am studying the subject and I am having hard time finding out if the theory is valid for all possible...
Current leading voltage or vice versa concept
3 hours ago Hello, I was wondering if there is a conceptual explanation for when current leads voltage or vice versa for capacitors or inductors with AC...
Angular Frequency of AC voltage
7 hours ago Hello, I am wondering, what is the physical interpretation of the angular frequency of AC voltage? I don't see the physicality of what the angle...
Modeling Rigid Body - Unsure about Euler angles and angular velocity
7 hours ago I'm modeling a single 3D rigid body in preparation for some more complicated modeling in order to gain a better understanding of Euler angles, the...
Function for a bullet's path
8 hours ago I've been mulling this over all weekend, and I've decided to get some help on this. The problem is writing a function to describe a bullet's path....
Elementary questions relating to Newton's laws of motion
10 hours ago i) If a wall breaks when it gets hit by a cannonball, did the wall exert an equal and opposite force on the cannonball? ii) Would the force...
- More from Physics Forums - Classical Physics
More news stories
(HealthDay)—Practitioners might consider discontinuing prophylactic antibiotics for patients with prosthetic implants undergoing dental procedures, and these patients should be encouraged to maintain appropriate ...
Dentistry May 14, 2013 | not rated yet | 0
A new report assessing the economic viability of services provided by practicing midlevel dental providers in the U.S. shows that they are expanding preventive dental care to people who need it most: children and those who ...
Dentistry May 14, 2013 | not rated yet | 0
(HealthDay)—Manifestation of dental erosion caused by illicit drug use or excessive soda consumption needs to be distinguished from dental caries, according to case studies published in the March/April ...
Dentistry May 13, 2013 | 5 / 5 (1) | 0
Are you wrecking your teeth without even knowing it? For instance, chewing on ice or opening stuff with your teeth may be convenient but using your teeth as tools can cause them to crack or chip.
Dentistry May 03, 2013 | 3 / 5 (1) | 1
Elderly or people with osteoporosis, smokers, diabetics or people who have had cancer are sometimes not eligible to receive dental implants as their bones are unable to correctly integrate the new prostheses which replace ...
Dentistry Apr 29, 2013 | not rated yet | 0
Johns Hopkins researchers say they have discovered specific chemical alterations in two genes that, when present during pregnancy, reliably predict whether a woman will develop postpartum depression.
57 minutes ago | not rated yet | 0 |
Children who have suffered maltreatment are 36% more likely to be obese in adulthood compared to non-maltreated children, according to a new study by King's College London. The authors estimate that the prevention or effective ...
57 minutes ago | not rated yet | 0
(AP)—The decade-old law that transformed the battle against HIV and AIDS in developing countries is at a crossroads. The dream of future generations freed from the epidemic is running up against an era ...
41 minutes ago | not rated yet | 0
(Medical Xpress)—A research team, led by Jeremy Barr, a biology post-doctoral fellow, unveils a new immune system that protects humans and animals from infection.
10 hours ago | 4.6 / 5 (13) | 4 |
New research suggests that a compound abundant in the Mediterranean diet takes away cancer cells' "superpower" to escape death. By altering a very specific step in gene regulation, this compound essentially re-educates cancer ...
13 hours ago | 4.8 / 5 (12) | 2 |
Early-life exposure to traffic-related air pollution was significantly associated with higher hyperactivity scores at age 7, according to new research from the University of Cincinnati (UC) and Cincinnati Children's Hospital ...
4 hours ago | not rated yet | 0 |