نتایج تحقیقات مارک ریچاردسون که در روز سه شنبه گذشته (23 آذر ماه) در سایت اخبار پزشکی Medscape انتشاریافت، نشاندهنده آلوده شدن میلیونها آمریکائی با جیوه موجود در مواد دندانپزشکی است. متن کامل خبر در این بخش ارائه میشود.
Mercury Exposure Due to Dental Fillings of Superfund Site Magnitude: Biologist
Robert Lowes
December 15, 2010 — Millions of Americans with mercury-based dental fillings are exposed to levels of mercury vapor that qualify toxic waste sites for the federal Superfund program, a scientist told an advisory panel of the US Food and Drug Administration (FDA) yesterday.
The scientist, biologist G. Mark Richardson, PhD, appeared among a parade of researchers, dentists, and consumer advocates who spoke for and against the use of mercury-based fillings — also known as dental amalgam — on the first day of a 2-day hearing of the FDA’s dental product panel.
Last year, the agency reclassified dental amalgam from a lower-risk class I medical device to a moderate-risk class II device with a new label stating that fetuses and young children may be more sensitive to its neurotoxic effects. Nevertheless, the agency declared that the material was safe for adults and children aged 6 years and above.
Opponents of dental amalgam, who link it to diseases ranging from autism to Alzheimer’s, have petitioned the agency to reconsider its 2009 decision and either ban the filling material or classify it as a high-risk class III device. The FDA convened the advisory panel to hear out these opponents, but not to recommend new regulations for dental amalgam.
Two prime questions for the panel are how much mercury is absorbed by people with dental amalgam and what the reference exposure level (REL), or safety threshold, for mercury vapor should be. Estimated mercury doses can be calculated from exposure levels to the vapor.
In its 2009 decision, the FDA put the mercury dose absorbed by individuals with 7 to 10 amalgam fillings at 1 to 5 μg/day. The range is roughly identically to permissible doses for children and adults derived from an REL for mercury vapor — 0.3 μg/m3 — set by the US Environmental Protection Agency (EPA). Such an REL, also called a reference concentration, is considered safe for even the most susceptible individual.
Dr. Richardson, the lead author of a dental amalgam study commissioned by a group advocating mercury-free dentistry, disagrees with the FDA’s daily dose calculation and states that the amount of mercury absorbed can range up to 22 μg, based on a conservative scenario of amalgam use. In his study, he estimates that 67 million Americans with dental amalgam exceed the permissible mercury dose associated with the EPA’s REL.
Dr. Richardson told the panel that RELs such as those for mercury vapor “do mean something.”
Of 1500 toxic waste sites in the EPA Superfund program, almost half contain elemental mercury, according to Dr. Richardson. Those mercury-contaminated sites make it on the list “because levels of exposure…exceed the EPA reference dose.” RELs and reference doses, he said, also shape guidelines for cleaning up these sites.
“When they’re cleaned up, the doses from those sites should not exceed the [REL],” said Dr. Richardson, a former employee of the Canadian equivalent of the US Department of Health and Human Services who now works for the environmental division of a Canadian engineering and construction firm.
Dr. Richardson believes that the EPA’s REL for mercury vapor is set too high and views the REL of 0.3 μg/m3 used by the California EPA as more accurate. All Americans with dental amalgam — some 122 million of them — are exceeding permissible mercury doses linked to this stricter safety threshold, according to Dr. Richardson.
“I Have Amalgams in My Own Teeth”
During a public comment section of the hearing, representatives of organized dentistry countered claims by Dr. Richardson and others that dental amalgam is a public health threat.
Dennis Charlton, DDS, president-elect of the Pennsylvania Dental Association, asserted that millions of patients have used dental amalgam with no adverse effects. He explained that mercury, normally toxic to humans, is rendered harmless by its combination with other metals in dental amalgam, just as poisonous chlorine gas combines with sodium to form perfectly safe sodium chloride — otherwise known as salt.
Dr. Richardson’s research came under fire from Rod Mackert, DMD, PhD, a dental materials researcher and professor in the School of Dentistry at the Medical College of Georgia in Augusta. Dr. Mackert, speaking on behalf of the American Dental Association, said Dr. Richardson reached his “ludicrous” assertions about the need for a lower REL for mercury vapor by discounting valid studies and relying on a flawed one.
A number of dentists told the panel that their support of dental amalgam has nothing to do with their economic self-interest, as some critics charged.
“I have amalgam in my own teeth, and I have used it to treat members of my own family,” said Jonathan Knapp, DMD, from Bethel, Connecticut, a member of the American Dental Association’s Council on Dental Practice. “If had any doubt — any doubt — about the safety of amalgam, I would never use it to treat my family.”
Mercury Issue Rarely Mentioned to Patients
Another contingent of dentists was on hand yesterday to denounce dental amalgam and tout mercury-free alternatives.
“Mercury exposure is no longer a price we have to pay to be successful in restorative dentistry,” said Stephen Koral, DMD, from Boulder, Colorado, a past president of the International Academy of Oral Medicine and Toxicology, which opposes the use of dental amalgam.
“I learned mercury was toxic in the second grade,” added Janet Stopka, DDS, from suburban Chicago, Illinois. “Mercury fillings have been a 200-year-old mistake.”
The panel also heard a number of individuals who bore painful witness to a host of health problems such as panic attacks, memory loss, food allergies, hypertension, metabolic syndrome, and cancer that they attributed to dental amalgam fillings and subsequent mercury poisoning. Several of them said their conditions subsided after they had these fillings replaced with mercury-free substitutes. They might have avoided their ordeals, they said, if their dentists had informed them about the risks of dental amalgam.
“Placing mercury in the mouths of patients is reckless and dangerous, and I am proof of that,” said Stephanie Bernier-Adamson from Fullerton, California. “The issue of mercury was never mentioned in any dental office where I was a patient.”
