Exposure of Dental Workers to Mercury
HERBERT BUCHWALD, Ph.D.*
Division of Industrial Health Services, Alberta Department of Health, Edmonton, Alberta
The work environment and procedures of twenty-three dentists and their assistants were surveyed for the existence of potential health hazards which could be associated with the preparation of mercury amalgam fillings. Data were collected on the work environment, ventilation, individual procedures, and hazard awareness related to the removal of old amalgam fillings as well as the preparation of new fillings. The results indicated that the greatest potential hazard may result from contamination of hands after working with mercury metal or fresh amalgam. Respirable dust, in terms of total concentration and mercury content, was also significant.
This study also demonstrated the almost complete unawareness of most dental assistants and of many dentists that mercury could be hazardous; consequently, precautionary measures were almost nonexistent.
A list of recommended precautionary measures is presented.
Contamination of the environment by mercury and its compounds is currently receiving a great deal of attention. The potential hazard to dental workers from mercury used in the preparation of restorative amalgams is no exception.
Observations regarding the safety of mercury in dental practice continue to be made on a regular basis, ranging from serious warnings to reports that there is little risk. In view of the ubiquitous use of mercury amalgams in dental offices, it is not surprising that the fatal intoxication of a dental assistant was eventually reported. 1 Frykholm,2 Noe,3 McCord,4 Preussner et al., 5 Nixon and Smith,6 Joselow et al., 7 and Gronka et al. 8 suggested hygienically significant exposures to mercury in dental offices.
In a survey of fifty operating rooms, Joselow and his associates found the average concentration of mercury vapor to be 0.020 .mg/m3 (range 0.002 to 0.160) and the average total concentration of mercury (vapor plus amalgam dust) to be , 0.045 mg/m3 (range 0.005 to 0.18).
In fifty-nine offices Gronka and his associates found an average exposure to mercury vapor of 0.027 mg/m3 (range 0.005 to 0.180).
The above studies had not included other parameters of mercury absorption into the system (for example, orally by transfer from hand and fingers to food or cigarettes, or by nail biting; by absorption through the skin of the hand ; by inhalation following transfer from fingers to cigarettes).
Our interest in this subject dates back to February 1966, when a request was received from the Edmonton Dental Association to determine if mercury was a hazard to health in dental offices. In a pilot investigation, urine specimens for mercury analysis were obtained from four dentists and their assistants.
From eight specimens collected in March 1966, the average mercury concentration was 0.16 mg/liter, the range being 0.06 to 0.37 mg/liter. Specimens obtained in August 1966 from five of the eight individuals showed an average mercury concentration of 0.06 mg/liter, with a range of 0.01 to 0.19 mg/liter. Cumulative urine specimens from several voidings on the same day were collected in each case.
Control analyses on several nonexposed subjects all showed mercury concentrations less than 0.03 mg/liter.
The results indicated significant absorption of mercury by the dental workers; the seasonal variation was not unexpected, since the ventilation of the offices was reported to be considerably better during the summer months.
In view of the significant results, a more comprehensive study was carried out during the summer of 1968, the results of which are the basis of this report.
Recommended Precautions for Safe Use of Mercury by Dental Workers
All persons working with or handling mercury should be instructed in the potential harm to health and in the methods for preventing absorption into the system.
(a) All mercury, including waste andl amalgam residues, should be stored in wellÂ·sealed containers. Waste mercury should not be flushed down the sink, placed in the garbage, or kept in beakers, trays, or other open containers. (Suitable containers include plastic, glass, and glazed ceramic; metal containers should be avoided.)
(b) Store mercury in a cool place.
(c) Never heat (even above 100Â°F) mercury except under exhaust ventilation (for example, under a fume hood).
(a) Articles contaminated with mercury (paper tissue, chamois leather, squeeze cloths, etc.) should be kept in sealed containers until disposal is possible (polyethylene bags are suitable); these may then be disposed in the normal garbage collection.
(b) All droplets or larger amounts of waste mercury, including pieces of new or old amalgam, should be accumulated in a sealed container until sufficient is available for return to the supplier or for sale to scrap metal dealers for recovery of mercury and silver. A layer of water over the mercury will reduce the possibility of vaporization.
4. Working Environment
(a) Mercury should not be used in small unventilated rooms.
(b) In rooms where mercury is used!, floors should be of smooth plastic, linoleum, or terrazzo with a minimum of cracks, corners, or fissures. Absorbewt floors such as carpet or worn wood should be avoided, since it is impossible to decontaminate these properly after accidental spills.
(c) Wooden benches and counter tops with cracks and corners should be sealed to prevent entry and accumulation of mercury. (One easy way of doing this is to tape heavy-gauge polyethylene sheet over the working surfaces.)
(d) Take care not to place hot objects or lighted cigarettes on surfaces where mercury is being used.
5. Prevention of Spills
(a) Care should be exercised to prevent spillage of mercury; the use of funnels and proper dispensers can be recommended. Apparatus used for dispensing mercury should be properly designed and maintained and in good condition.
(b) All dispensing of mercury, mulling, or other preparation of amalgam should be done over a suitable tray in which any pills or drops will be caught. Triturators or other equipment used in conjunction with mercury can be placed on a shallow tray large enough to catch any stray droplets.
(c) The use of encapsulated materials can be recommended.
6. Clean-up Spills
(a) Spilled mercury should be cleaned up immediately.
(b) Never use bare hands for wiping over contaminated surfaces. A paper tissue can be used effectively to sweep together many small droplets for agglomeration into larger drops.
(c) Droplets in difficult places may be picked up with narrow-bore tubing connected (via a suitable trap) to a vacuum pump. A vacuum cleaner should not be used for cleaning up spills.
(d) Droplets in inaccessible places should be treated with a mercury absorbent paste composed of equal parts of calcium oxide (hydrated), flowers .ofsulfur, and water.
7. Personal Hygiene
(a) Mercury can be absorbed through the skin. Care should be taken not to handle metallic mercury or contaminated equipment. If it is necessary to handle mercury, the hands should be washed thoroughly as soon as possible afterwards.
(b) Mercury can be transferred from contaminated surfaces or hands to cigarettes and then inhaled directly after being volatilized by the heat. The heat from a burning cigarette can also volatilize significant amounts of mercury if the cigarette is placed on a contaminated surface. Smoking should be prohibited in areas where mercury is being used, and persons who have worked with mercury should not smoke until the hands have been washed.
8. Medical Examination
Periodic blood and/or urine analyses for mercury should establish if persons are absorbing potentially harmful amounts. (every 3, 6, or 12 months, according to the degree of exposure). Advice regarding such analyses can be obtained from the Occupational Health Branch of the Provincial Department of Health.