the mercury in your teeth

THE MERCURY IN YOUR TEETH

http://depts.washington.edu/envhlth/info/newsletter_html/winter99.html

Going to the dentist today to have a tooth filled? If so, chances are your filling will be made of an alloy containing about 50 percent mercury, the standard amalgam used around the world for dental restoration work. Millions of mouths contain mercury fillings, yet definitive research is still underway as to whether or not mercury amalgams represent a human health concern.

The dangers of high-level mercury exposure have long been recognized. Whether mercury amalgams (which also contain silver and other materials) represent a case of chronic, low-level mercury hazard has yet to be determined. Two scientists connected with the Department of Environmental Health, Professor Jim Woods and Affiliate Associate Faculty member Diana Echeverria of the Battelle Centers for Public Health Research and Evaluation, are addressing the issue.

Dr. Woods is currently active in projects involving two different age groups in two different countries: 500 children in Portugal and 400 dental assistants and dentists in Seattle. Dr. Woods is collaborating with Dr. Echeverria in the latter project. Their research is funded by two institutes of the National Institutes of Health, the National Institute of Dental Research and the National Institute of Environmental Health Sciences.

Mercury toxicity affects, especially, the central nervous system and the kidneys, which are its storage sites. According to Dr. Woods, it was once believed that mercury alloys, when fully hardened in a tooth, remained more or less inert; however, we have since come to realize that the material slowly leaches, helped along by saliva. A very small amount is swallowed and simply passes through the body like many other substances; a greater amount vaporizes and enters the lungs. From there it goes into red blood cells and eventually affects the central nervous system. A portion of vapor is oxidized in plasma and ends up in the urine.

Mercury vapor, especially, is very toxic. Dentists and dental assistants come into contact with vapor when preparing amalgams. As the hazards of handling mercury have become more recognized, dental professionals have handled it with more care--squeezing it from a capsule under well-ventilated conditions, using protective gear. With more careful handling, mercury in the urine of tested Washington State dentists has shown a steady decline since the 1970s. Dentists now typically have urinary mercury levels similar to the levels in the general population. Several uses of mercury, such as putting the substance into latex paint, have been abolished; however, people may be exposed through food (especially fish); through certain occupational exposures (such as work with hazardous wastes, thermometer or barometer manufacture, some chlorine-related manufacturing processes); and through releases from fossil fuel power plants and incinerators, to list a few possibilities.

Exposure tests

To evaluate chronic, low-level mercury exposure from amalgams, Drs. Woods and Echeverria will do various kinds of testing. To measure vapor exposure, the team will place air monitors in dental settings, and the 400 volunteers will wear mercury-registering dosimetry badges. Blood and urine samples will be taken twice, at six month intervals, and tests given for kidney functioning and for how a rare mercury allergy affects the kidneys.

In addition, urine samples will be evaluated for substances called porphyrins. Five porphyrins are normally excreted in the urine. Dr. Woods and colleagues have discovered that there is a change in the porphyrin excretion pattern that is unique to mercury. Some of the porphyrins that normally are present in urine in low concentrations increase dramatically when mercury is retained in the kidneys, the principal body storage site. The particular porphyrins that are affected by mercury can therefore be used as metabolic biomarkers of mercury body burden. Some of the volunteers who have elevated urinary porphyrins will be treated with a drug (called a chelating agent) that binds with mercury in the kidneys and facilitates mercury excretion in the urine. A decline in urinary porphyrin levels after removal of mercury from the kidneys by chelation would confirm that elevated urinary porphyrins accurately reflect mercury retention in body tissues.

Dr. Echeverria will evaluate the central nervous system of volunteers with a standardized battery of tests that she has developed over the past ten years. Mercury is known to affect cognitive and other functions. Cognitive tests--some done on a computer--will measure such things as various kinds of memory; attention span and the ability quickly to switch one's attention; visual and spatial abilities; mood (tension, depression, anger, fatigue, confusion); and motor function. In addition, another set of tests will measure postural sway, imbalance, heart rate interval, nerve conduction velocities, and sensitivity to vibration and smell. Dr. Echeverria will be looking for potential shifts in behavior at very low mercury exposure levels.

Dr. Echeverria noted that, for dentists, any problem with motor skills (such as poor coordination or tremor) is a potential problem, since dentists need steady hands to work with drills and small instruments. Motor problems correlate with a finding of about 5&endash;10 micrograms of mercury per liter in urine; Washington State dentists evaluated in the 1970s and early 1980s averaged above the upper level of this urinary range, but now typically measure around 3 micrograms per liter. One kind of coordination test requires participants to place a pen in a series of holes with decreasing diameters without hitting the sides. Researchers have observed a clear dose-response effect with increasing mercury concentration.

Long-term project

Drs. Woods and Echeverria are expecting to have their correlated results in about another year. The children's study in Portugal with which Dr. Woods is involved is just beginning its third year and will probably continue for a minimum of seven to eight years. Funding is being provided by the National Institute of Dental Research, and a team of interdisciplinary researchers from the University of Washington, including lead scientists from the UW School of Dentistry, is taking part.

In this study, the 500 children participating are 8 to 10 years old (thus beyond the age for loss of their baby teeth) and are from backgrounds that have not allowed necessary dental care. Pilot studies established that their prior exposure to mercury (or lead) was insignificant. It will be usual for these children to need 15-20 fillings; they have lacked the opportunity to drink fluoridated water, which has now more or less eliminated the need for fillings in the teeth of most US children. Some of the Portuguese children will receive the usual mercury amalgams and others will receive a composite made of a mixture of acrylic resin and finely ground up porcelain. The work will be done at the School of Dentistry of the University of Lisbon. Extensive behavioral and neurological tests will be administered before and after dental treatment and urine monitoring will be done. This is one of the first studies focusing on the safety of mercury amalgams for children, who are, generally speaking, more sensitive to toxicants than are adults.

Dr. Woods observed that any substitute for mercury in amalgams should have certain qualities. It must not be so costly that people will see a dentist less often; it must be durable; and it must have "expansive" properties that enable it, once inserted, to fill in all crevices of a tooth cavity, leaving no air pockets.

Neither Dr. Woods nor Dr. Echeverria recommends that mercury amalgams in one's mouth be replaced, barring some unusual circumstance, such as an allergy to mercury. This is because mercury vapor is released in excavating a filling for replacement. While Dr. Echeverria noted that such decisions are personal ones at the present state of knowledge, she commented that "the person who will feel the benefit [of replacement] is rare." --PC

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MERCURY IN WONDERLAND

In Lewis Carroll's tale of Alice, why is the hatter mad?

Although the hatter pours tea over the dormouse and has an eccentric view of Time, he's really no "crazier" than many of the other characters in Alice in Wonderland. But according to Martin Gardner, author of The Annotated Alice, the phrase "mad as a hatter" was common at the time Carroll wrote, and a reason for Carroll's creation of his "mad" hatter.

Gardner writes that the "mercury used in curing felt [for hats] was a common cause of mercury poisoning. Victims developed a tremor called 'hatter's shakes,' which affected their eyes and limbs and addled their speech. In advanced stages they developed hallucinations and other psychotic symptoms."

Felting involves the interlocking of materials--such as wool, fur, and certain hairs--that, because of their structure, can be combined without adhesives. In an interesting 1992 article in Occupational Medicine, Dr. Martin Cherniack explains that felters applied a solution of mercury and nitric acid to rabbit skins. The fur was then dried, cut, and brushed. So dusty was this procedure that mercury levels in air "could range from...100-1000 times the [US early 1990s] workplace exposure limit."

As the dangers of mercury were recognized, the British Parliament took action to outlaw uses by the mid-1860s. In the US, important mercury exposure studies were done in the 1920s. However, a US Public Health survey of 25 felt-hat plants as late as 1941 found widespread use of mercury and of mercury-induced symptoms. --PC

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Assessing worker exposures

The Department of Environmental Health has a weekly Seminar Series for students and faculty, which features speakers from within the department, public agencies, and other university departments. During autumn quarter, DEH faculty member Michael Morgan presented a talk, from an industrial hygienist's perspective, on biomonitoring in the workplace. A report on some of his remarks, supplemented by a later interview, follows. Professor Morgan directs DEH's Undergraduate Program.

Consider this scenario: Workers using a powerful solvent suspect that levels of a chemical in the air around them are not being accurately recorded by air monitors in the room where they work. Although the monitors are recording low levels, the odor of solvent is very strong. They raise this issue with their union representative, who in turn raises it with their manager. Eventually arrangements are made for biomonitoring.

What is biomonitoring? While there are different kinds, used for different purposes, that employed by industrial hygienists involves the planned, repeated collection, over time, of some form of biological specimen--most commonly urine, blood, expired air, or a secretion such as saliva or sweat. While ambient air monitoring has served us well in the past to protect workers from toxic chemicals, and should almost always be employed in conjunction with biomonitoring (so that "body readings" and monitor readings can be compared), inhalation is not the only route by which a chemical enters the body. Thus the use of biomonitoring as an adjunct to air monitoring should be considered.

From the standpoints of both workers and employers, Dr. Morgan noted, biomonitoring can be seen as having both positive and negative attributes. Among the positives are the fact that biological specimens taken from workers will account for such routes of exposure as skin contact, because the specimen will "sum up" all exposures; can take into account how chemicals are processed differently in different individuals; can reveal nonoccupational exposures to chemicals (if a worker's specimens, say, reveal differences on a Monday morning following a weekend off); and can help test the performance of protective equipment, since specimens can be taken both before and after equipment use.

Among the possible drawbacks are such problems as worker dislike and suspicion of being monitored; the fact that monitoring is a repetitive process that may require a good deal of data collection before results can be interpreted; and the process can be expensive, both in terms of the costs of lab analysis and because certain professionals may need to be added to the monitoring team if some kinds of specimens--blood samples, for instance--are to be collected.

International differences

There are interesting international differences in attitudes towards biomonitoring in societies across the world. In such places as Japan and Sweden, for example, as well as in other countries of Europe, biomonitoring is simply something that is done. In the US, workers tend towards more suspicion of their employers, with concerns about how data will be used and what employers are "really" looking for, such as illegal drug use. Biomonitoring can also be seen as an unwanted nuisance at the end of a long day or week. For these and other reasons, workers are perhaps as likely to reject biomonitoring as to accept it, unless they are, as in the scenario with which this story opened, concerned about some toxic hazard. The presence of a labor union, representing an opportunity for organized worker discussion, may make workers more inclined to biomonitoring than they would otherwise be.

One question to be asked when considering biomonitoring is whether there is a definitive analytic method available for dealing with a suspected problem. In testing for exposure to the solvent toluene, for instance, one needs to know that toluene taken into the body is largely metabolized into hippuric acid. However, finding a large amount of hippuric acid in a urine sample is not a reliable indicator of toluene exposure, because hippuric acid also appears in urine as a result of eating such foods as cereals, fruits, and vegetables. Since hippuric acid is not a good indicator of toluene exposure, hygienists instead look at the level of o-Cresol (ortho-Cresol), even though only about 1 percent of toluene is converted into o-Cresol. In the case of another substance, benzene, experience has led hygienists to switch from looking at phenols in urine samples to examining, instead, mercapturic acid.

finding any substance in urine or some other bodily excretion does not take one too far without a guideline or standard of comparison to help interpret what the presence of the substance at that level might mean. Here the work of professional associations and government agencies comes into play.

Dr. Morgan is currently chair of the BEI Committee of the American Conference of Governmental Industrial Hygienists (ACGIH). This international committee, made up of volunteer scientists and practicing professionals in a variety of fields, has the job of developing reference values against which observed biological concentrations of a substance may be compared, in order to form judgments about workplace conditions. The reference values are published as a list of Biological Exposure Indices--BEIs--and are periodically reviewed as new scientific information becomes available. The review process involves many steps and has been described in an article by Dr. Morgan that is referenced at the end of this story. See the table below for examples of how reference values are set forth. The complete ACGIH list contains approximately 35 compounds or groups of compounds; another list, compiled in Germany, contains about 40 compounds, with overlap between these two major lists. Much important biomonitoring work is now being done in Europe.

In the US, the Occupational Safety and Health Administration has made biomonitoring mandatory for only two substances to which workers may be exposed: lead and cadmium. So much is now known about the dangers represented by different levels of lead in the blood, in fact, that it is one of only two cases in which the ACGIH does not correlate blood sample results with monitor readings. Cholinesterase inhibitors--found in pesticides--are the other case.

Dr. Morgan described one company's experience with worker exposure to N, N-dimethylacetamide, a solvent used in making acrylic fibers. Although air monitors usually showed acceptable (or even better) air conditions, both the company and workers were aware that some kind of chemical contact was occurring; the question became whether the protective gloves used by workers were performing adequately. A three-month biomonitoring study, involving urine specimens, showed that in some workers skin absorption was indeed taking place. While it is not known how many US companies have done or are doing biomonitoring, because there is no developed reporting system, this case demonstrated that a biological indicator revealed much more about worker exposure to a chemical than did air monitoring alone.

Dr. Morgan concluded his talk by noting that the future will bring industrial hygienists new tools, as research is done to develop molecular biomarkers, better sampling techniques, and more data on how chemicals are processed within the body. These tools should contribute to the principal goal of the industrial hygienist: the prevention or minimizing of work-related illness. --PC

For Further Reading

Morgan, M. 1997. The Biological Exposure Indices: A key component in protecting workers from toxic chemicals. Environmental Health Perspectives 105 (Supplement 1, February): 105&endash;115.

Chemical Agent	Biological Exposure Index	Reference Value	First Adopted	Last Revised
Acetone	Acetone in urine	50 mg/liter	1994	1999
Cobalt	Cobalt in urine	15 mg/liter	1995
	Cobalt in blood	1 mg/liter
Lead	Lead in blood	30 mg/dl	1987	1995

* The chemical agents listed here are chosen merely as examples. As explained in Dr. Morgan's article in Environmental Health Perspectives (see For Further Reading), the BEI for lead has been set at a level to prevent or minimize effects that are believed to result in persistent functional impairment of the worker or his or her offspring. Certain effects may be seen at blood lead levels below the BEI of 30 micrograms per deciliter, but are not believed to represent significant impairment for various reasons. Few substances of health significance have been so thoroughly studied by epidemiologists as has lead. Abbreviations used above: mg = milligram; mg = microgram; dl = deciliter.

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CONTINUING EDUCATION

For course details, call (206) 543-1069, or visit the Web. Upcoming courses:

NW Center for Occupational Health & Safety

Mar 16-18 Hazardous Materials Incidents: Improving Interagency Response (Bellingham, WA)

Mar 22-26 Comprehensive Review of Industrial Hygiene

Mar 30 Ergonomics in the Forest Products Industry

April 8 Safety & Health in Commercial fishing

April 20 Occupational Skin Disorders: Management and Prevention

April 28 Effective Worker Training: What Safety & Health Professionals Need to Know

May 27 Implementing An Ergonomics Program in Your Workplace (Anchorage)

OSHA Training Institute Educational Center

Mar 15-18 OSHA 600: Collateral Duty Course for Other Federal Agencies

Mar 22-25 OSHA 501: Trainer Course in OSHA Standards for General Industry

Apr 5-7 OSHA 226: Permit-Required Confined-Space Entry

Apr 14-16 OSHA 502: Update for Construction Industry Outreach Trainers

Apr 19-21 OSHA 503: Update for General Industry Outreach Trainers

Apr 26-29 OSHA 201A: Hazardous Materials

May 3-6 OSHA 510: OSHA Standards for the Construction Industry

May 7 OSHA S: Scaffolding Users Course

May 10-13 OSHA 500: Trainer Course in OSHA Standards for The Construction Industry

May 24-27 OSHA 309A: Electric Standards (Portland)

June 2 OSHA 225: Principles of Ergonomics

June 7-10 OSHA 501: Trainer Course in OSHA Standards for General Industry

FOUR-DAY COURSE IN SEATTLE

Comprehensive Review of Industrial Hygiene March 22-26, 1999

This special course is specifically designed to assist practicing industrial hygienists in preparing for the American Board of Industrial Hygiene (ABIH) core and comprehensive exams (it is not intended for entry level professionals). Sponsors are DEH's Northwest Center for Occupational Health and Safety and the Center for Occupational and Environmental Health of the University of California at Berkeley. Classes will meet at the HUB on the UW campus; however, registration is through the Berkeley center. For more information, call (510) 231-5645 or use the Web home page at http://socrates.berkeley.edu/~coehce/.

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