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MERCURY; A POISONOUS HAZARD OF THE DENTAL OFFICE

R o b e r t G r i f f i t h , D.D.S.

T h a t hazards f rom v a p o r i z e d mercury i n t h e p r a c t i c e o f d e n t i s t r y e x i s t has t r o u b l e d i n d u s t r i a l h y g i e n i s t s and t h e pe rsonne l p romot ing occupa t iona l h e a l t h f o r some t ime. References have appeared r e c e n t l y i n the l i t e r a t u r e o f s c i e n t i f i c groups which c a l l a t t e n t i o n s p e c i f i c a l l y t o t h e s e haza rds i n t h e p r a c t i c e o f d e n t i s t r y . I n d e n t a l schoo ls , l i t t l e o r no a t t e n t i o n appears t o have been p a i d t o t h e r i s k of vapor- i z e d mercury t o h e a l t h i n p r i v a t e p r a c t i c e o r i n d e n t a l c l i n i c s . A number o f d e n t i s t s have exp ressed a comp le te l a c k o f conce rn a b o u t hand1 ing mercury.

I n numerous o f f i c e s , i t appears, d e n t i s t s have become so accustomed t o h a n d l i n g mercu ry t h a t t h e y n e v e r t h i n k o f i t as an o c c u p a t i o n a l hazard. Warnings have begun t o appear, however t h a t mercury may be- come a source o f se r ious c h r o n i c i l l n e s s .

The r e p o r t , which f o l l o w s , w i l l e x p l o r e t h e problem o f exposure o f d e n t i s t s t o t h e vapor o f mercury . I n o r d e r t o assess t h e hazard o f such exposure d u r i n g r o u t i n e c l i n i c a l procedures, t h e o p e r a t o r ' s p ro - cedures w i l l have t o be examined t o de te rm ine such c o n d i t i o n s as t h e ar rangement o f t h e o p e r a t i n g room and some o t h e r p e r t i n e n t f a c t o r s . The f o l l o w i n g f a c t o r s a p p e a r p e r t i n e n t i n s t u d y i n g t h i s haza rd :

1. 2. 3. 4. 5. 6. 7. 8- 9.

10. I I .

12. 13.

c 1 ean 1 i ness o f the o f f i c e , v e n t i l a t i o n , s p i l l a g e d u r i n g amalgamation o f a l l o y , temperature o f t h e room. the years used i n a den ta l o f f i c e , t o t a l personnel exposed, medical and den ta l f i nd ings , person p repar ing t h e amalgam, approximate amount of o p e r a t i v e se rv i ces completed d a i l y , method of d i sposa l o f scrap, t h e method o f d i s p o s a l o f f r e e mercury expressed from the amal- gam through a squeeze c l o t h , p rev ious a n a l y s i s of t he a i r , and v a r i o u s ins t ruments and dev ices which may i n f l u e n c e t h e concen- t r a t i o n o f mercury as a vapor.

REVIEW OF THE LITERATURE

Hami l ton8, i n 1925, repo r ted t h a t mercury, as a mobi le, 1 i q u i d metal, v o l a t i l e a t room tempera ture , gave o f f vapor which would be hazardous when t h e c o n c e n t r a t i o n exceeded 0.1 m i l l i g r a m per c u b i c meter of a i r .

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I n 1938, Nea l i4 c a l l e d a t t e n t i o n t o t h e v a l u e w h i c h d e l i m i t e d t h e t h r e s h o l d (maximal a l l o w a b l e c o n c e n t r a t i o n ) , based on an e i g h t - h o u r

Members o f t h e Med iz in i sche K I i n i k i 2 o f Germany concluded, i n 1926, t h a t c h r o n i c p o i s o n i n g was p o s s i b l e i n peop le work ing f o r a l o n g per- iod, i n a room i n which t h e thermometer has been broken and the mercury al lowed t o remain on the f l o o r . Souder and Sweeneyi6, i n 1931, repor ted t h a t a d r o p l e t of mercury i n a c l e a n o f f i c e would g i v e o f f a g r e a t e r c o n c e n t r a t i o n of vapor than i n an unc lean o f f i c e because t h e d u s t and o t h e r subs tances formed p r o t e c t i v e c o v e r i n g s around t h e d r o p l e t and i n h i b i t e d v a p o r i z a t i o n . Grossman and Dannenberg7 p o i n t e d o u t i n 1949, t h a t " s l i g h t ( b u t n o n - t o x i c ) amounts of mercury vapor a r e p r e s e n t i n t h e a i r of d e n t a l o f f i c e s , and t h a t t h e c o n c e n t r a t i o n o f mercury vapor i s d i r e c t l y p r o p o r t i o n a l t o t h e amount o f mercury used by the i n d i v i d - ua l d e n t i s t . "

MeadlI , i n 1940, repo r ted t h a t repeated smal l doses o f mercury were more dangerous i n p r o d u c i n g m e r c u r i a l s t o m a t i t i s t han a s i n g l e l a r g e dose. Schour and Sarnat15, i n 1942, l i s t e d t h e symptoms o f m e r c u r i a l po i son ing as " s a l i v a t i o n , meta l1 i c t a s t e , u l c e r a t i o n s , hoarseness, fa- t i g u e , osteomyel i t i s , g i n g i v i t i s , and p e r i o d o n t i t i s . " Browning1, i n 1961, Hami l t on i n 1925, and Johnstone and M i l l e r g i n 1960, desc r ibed t h e symptoms o f p a t i e n t s a f f l i c t e d w i t h m e r c u r i a l i n t o x i c a t i o n as ma- l a i se, anorex i a , g a s t r o i n t e s t i n a l d i s tu rbances , d i a r r h e a , l a s s i tude, and anx ie ty about phys i ca l cond i t i on .

C u r t i s and T a y l o r 2 s t a t e d , i n 1947, t h a t pure mercury seldom was a s e n s i t i z i n g agent, b u t t h a t i t s s a l t s were prone t o be. Some d e n t i s t s have been unable t o work w i t h amalgams because o f s e n s i t i z a t i o n . Cur- t i s and Tay lo r , i n 1947, and Fernstrom, e t a l . , 4 i n 1962, agreed t h a t mercury was recognized as a s e n s i t i z i n g agent and t h a t i t cou ld produce a l l e r g i c r e a c t i o n s . Accord ing t o Webster17, i n 1949, "Substances en- coun te red i n v a r i o u s occupat ions and i n d u s t r i e s o r t h e i r p roduc ts a re capable o f induc ing eczematous s e n s i t i z a t i o n . "

Giese' s t a t e d , i n 1948, t h a t we l l - known s c i e n t i s t s , among them Faraday and Pascal, were v i c t i m s o f c h r o n i c po i son ing by mercury, even though t h e y were unaware o f exposure t o i t a t t h e t ime . Frykho lm5 s t a t e d , i n 1957, t h a t " t h e p o s s i b l e d e t e r i o r a t i o n i n h e a l t h as a con- sequence of exposure t o mercury from amalgam r e s t o r a t i o n s may be looked upon as a poisonous e f f e c t o f mercury o r as an a l l e r g i c m a n i f e s t a t i o n due t o o v e r s e n s i t i v i t y t o t h a t meta l . " F rykho lm summarized t h e pre- cau t iona ry measures which should be stressed, when engaging i n the pro- cedures of a den ta l o f f i ce , as care i n mixing, kneading, and e l i m i n a t i n g excess mercury. Knappl', i n 1962, s t a t e d t h a t mercury was an impor tan t m a t e r i a l and a s a f e one, i f p r o p e r l y hand led , b u t t h a t c e r t a i n p re - c a u t i o n s were necessa ry t o a v o i d t h e p o s s i b i l i t y o f some degree o f m e r c u r i a l po ison ing . Frykho lm s t a t e d t h a t a p r i n c i p a l source of t h i s v a p o r was f r o m m e r c u r y w h i c h had s p i l l e d on rough s u r f a c e s , where thorough removal was d i f f i c u l t . Temperature, s u n l i g h t , and v e n t i l a t i o n

d a i l y exposure, as 0.1 mg/m 3 .

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migh t a f f e c t t h e c o n c e n t r a t i o n o f vapor i n a room and, f o r these rea- sons, he s t a t e d t h a t i t was e s s e n t i a l t h a t areas, i n which mercury was used, shou ld be checked r e g u l a r l y i n o r d e r t o l o c a t e t h e sou rces o f hazardous vapor ized mercury. Exposure t o low a i r b o r n e concen t ra t i ons of mercury-vapor p o s s i b l y c o u l d r e s u l t i n c h r o n i c symptoms. The presence o f vapor ized mercury cou ld lead t o i l l n e s s which man i fes ted i t s e l f pre- dominately i n nervous and menta l d i so rde rs . The occupa t iona l hazards t o h e a l t h were s t a t e d by Frykho lm t o be g r e a t e r f o r t h e d e n t a l a s s i s - t an ts than f o r t he d e n t i s t s .

Meyer13, i n 1962, r e p o r t e d t h a t improvement o f t h e h e a l t h o f d e n t a l personnel would be accompl ished o n l y by adherence t o p r o p h y l a c t i c and s t r i c t h y g i e n i c measures. These measures would have t o be fo l l owed i n o r d e r t o p r e c l u d e ( I ) t h e r i s k o f i n t o x i c a t i o n , and ( 2 ) t h e r i s k o f s e n s i t i z a t i o n s i n c e the consequences o f a l l e r g y may n o t become man i fes t u n t i l years l a t e r .

Dalhamn3, i n 1953, and Meyer, i n 1962, concluded, on t h e b a s i s of r e s u l t s o f a n a l y s e s o f a i r and u r i n e , t h a t t h e r e was no s e r i o u s r i s k o f c h r o n i c m e r c u r i a l po i son ing f o r d e n t i s t s and den ta l nurses i n normal d e n t a l p r a c t i c e . Both Meyer and Dalhamn s t a t e d , however, t h a t t h e r e were many degrees o f i n t o x i c a t i o n and t h a t t he d e n t i s t and den ta l per - s o n n e l were p o t e n t i a l c a n d i d a t e s f o r m e r c u r i a l p o i s o n i n g .

APPRAISAL OF AVAILABLE INFORMATION

The occupa t iona l hazards t o h e a l t h have been s t a t e d by Frykholm t o be g r e a t e r f o r t h e d e n t a l a s s i s t a n t s than f o r d e n t i s t s , a r e s u l t which, o f course , would be expec ted s i n c e a s s i s t a n t s would be s u b j e c t e d t o v a p o r i z e d mercury f r e q u e n t l y d u r i n g m i x i n g and d i s p e n s i n g . Mercury as a poisonous hazard o f t h e d e n t a l o f f i c e has been accepted w i d e l y by invest igators,3,5,7,13 and l i t t l e research o f any s i g n i f i c a n c e has been added t o t h e o r i g i n a l obse rva t i ons and a n a l y t i c a l a n a l y s i s o f Frykholm i n 1957.

The c o n c e n t r a t i o n s o f m e r c u r i a l vapor have been found t o be t h e h i g h e s t i n t h e o p e r a t i n g rooms where t h e amalgamation and r e s t o r a t i v e procedures were performed. S tud ies have conf i rmed s c i e n t i f i c a l l y , t h a t t h e busy genera l p r a c t i t i o n e r s , whose p r a c t i c e s c o n s i s t e d o f a l a r g e p o r t i o n o f o p e r a t i v e procedures, had o f f i c e s i n which h i g h concent ra - t i o n s o f m e r c u r i a l vapor were found. Contaminat ion by mercury i n t h e d e n t a l o f f i ce , may be d e t e c t e d i n darkrooms, ha1 \ways, s t a i rways, re- c e p t i o n rooms, and baseboards. Mercury was found t o have been d i s - t r i b u t e d o v e r t h e f l o o r and a d j a c e n t a reas by mops, brooms, sponges, and t h e s o l e s o f shoes. I n v e s t i g a t o r s have d e m i n s t r a t e d t h a t v e r y h i g h read ings a r e o b t a i n e d i n o p e r a t i n g rooms where rugs, r a t h e r than l i no leum, have been used as f l o o r cove r ings . The i n v e s t i g a t o r s , who conc luded t h a t no r i s k o f c h r o n i c m e r c u r i a l p o i s o n i n g f o r d e n t i s t s and d e n t a l personne l e x i s t s , have based t h e i r s ta temen ts on ev idence which was l a r g e l y s u b j e c t i v e , c i r c u m s t a n t i a l and n o n s c i e n t i f i c . The v a l i d i n f o r m a t i o n now may be l i s t e d : ( I) v a p o r i z e d mercury i s known

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t o be a s e n s i t i z i n g a g e n t t h a t can produce a l l e r g i c r e a c t i o n s : (2) s m a l l doses o f mercury ove r an extended p e r i o d o f t i m e a r e more dan- gerous i n p roduc ing m e r c u r i a l s t o m a t i t i s than a s i n g l e l a r g e dose: ( 3 ) t h e s t a n d a r d f o r e i g h t - h o u r d a i l y exposure has n o t been accep ted as v a l i d comple te ly : (4) c h r o n i c i l l n e s s may be developed by t h e i nha la - t i o n o f vapor i zed mercury. I n f u r t h e r defense o f t he preced ing s t a t e - ments, i t may be s t a t e d t h a t supposed ly h e a l t h y p e o p l e can be found w i t h c h r o n i c m e r c u r i a l po i son ing , even though unaware o f exposure t o mercury a t t h e t ime. L a s t l y , t h e ev idence appears s u f f i c i e n t t o es- t a b l i s h t h a t c h r o n i c m e r c u r i a l i s m may produce s i g n s o f t o x i c i t y many years l a t e r .

The op in ions o f e a r l y i n v e s t i g a t o r s concern ing v e n t i l a t i o n appear t o have corroborated. Powerful v e n t i l a t i n g u n i t s were es tab l i shed as bene- f i c i a l , s i n c e mercury vapors a re n o t e a s i l y d isp laced. Heat was de te r - mined t o be another impor tan t f a c t o r t o cons ider i n t h e den ta l opera t ing room. Amalgamators p laced near r a d i a t o r s o r h e a t i n g dev ices obv ious l y would i nc rease t h e v a p o r i z a t i o n o f mercury. Grossman and Dannenberg may be quoted: "Unfor tunate ly , t he study was c a r r i e d o u t i n the sp r ing - t i m e when r a d i a t o r s and heaters , which m i g h t have increased t h e vo la - t i l i z a t i o n o f m e r c u r y , were n o t i n use."

V a l i d i n f o r m a t i o n demonstrated t h a t t h e read ings o f t h e meter were much h i g h e r nea r t h e f l o o r than a t t h e l e v e l o f b r e a t h i n g . I n v e s t i - g a t o r s have r e f e r r e d t o t r a n s i e n t a i r l e v e l s o f vapor i zed mercury i n t h e opera t i ng room which were above the va lue o f t h r e s h o l d - I i m i t (MAC). Mercury can be absorbed through t h e i n t a c t sk in , as w e l l as through the lungs , and t h e o r a l r o u t e o f i n t a k e a l s o must be cons ide red . Meyer suggested, i n 1962: "Fo r p r o t e c t i o n w h i l e m i l l i n g amalgam, cove r t h e h a i r and use a s u r g i c a l mask t o f i l t e r o u t p a r t i c l e s thrown toward the b r e a t h i n g zone." Meyer p r o v i d e d no s u p p o r t i n g ev idence t o e s t a b l i s h t h e c a p a b i l i t y o f a s u r g i c a l mask t o f i l t e r v a p o r i z e d mercury. I t i s i m p o r t a n t t o emphasize t h a t none o f t h e i n v e s t i g a t o r s used a n y t h i n g b u t i ns t rumen ts f o r d i r e c t r e a d i n g t o measure v a p o r i z e d mercury. I n t h e review o f t h e i r research on mercury, they f a i l e d t o s t a t e the c a l i - b r a t i o n o f t h e i n s t r u m e n t p r i o r t o e n t e r i n g each d e n t a l o f f i c e . I n d e t e r m i n i n g a i r b o r n e c o n c e n t r a t i o n s o f t h e vapor i zed mercury, t h e i n - s t rumen t must be a d j u s t e d i n an atmosphere f r e e o f vapor i zed mercury a f t e r each read ing i n o r d e r t o e l i m i n a t e e r r o r . I f c u r r e n t research s h o u l d p r o v i d e s u f f i c i e n t ev idence t h a t no s e r i o u s r i s k o f m e r c u r i a l p o i s o n i n g e x i s t s i n the d e n t a l o f f i c e , then i t would have t o be shown t h a t t he f o l l o w i n g fac to rs have been studied:

1 . S a m p l i n g p r o c e d u r e s t h a t a r e s t a t i s t i c a l l y Va l i d : 2. C o n s i d e r a t i o n o f v e n t i l a t i o n , t e m p e r a t u r e and a i r p r e s s u r e

3 . E l i m i n a t i o n o f nonaccu ra te i n s t r u m e n t s f o r d i r e c t r e a d i n g t o

The r e p o r t by Johnstone and M i l l e r l i s t e d 12 i ns tances o f c h r o n i c

ensu red :

d e t e r m i n e a i r b o r n e v a p o r i z e d mercu ry .

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m e r c u r i a l i n t o x i c a t i o n . S t o m a t i t i s , s a l i v a t i o n , and t remors o f t h e tongue and e y e l i d s , a l l o f which a r e c a r d i n a l s i g n s o f m e r c u r i a l p o i - soning, were absent. T h i s f i n d i n g may i n d i c a t e t h a t m ino r symptoms, such as insomnia, res t l essness , and i r r i t a b i l i t y , a l s o shou ld be con- s i d e r e d i n d i agnos i ng c h r o n i c m e r c u r i a1 i n t o x i c a t i o n .

From the survey o f t h e 1 i t e r a t u r e t h a t has been completed, t h e f o l - low ing v a l i d s ta tements may be suggested f o r reduc ing occupa t iona l ex- posu re :

1 . A l l mercury , i n c l u d i n g t h a t i n waste r e c e p t a c l e s , s h o u l d be s t o r e d i n an imperv ious c o n t a i n e r wh ich i s p r o v i d e d w i t h a t i g h t l y - f i t t e d l i d . The excess o f mercury expressed from d i s p o s a b l e squeeze c l o t h s should be c o l l e c t e d i n t h i s impervious con ta ine r . Extreme ca re should be taken i n s t o r i n g t h e mercury immediately a f t e r i t i s rece ived from the manufacturer.

Recommended p recau t iona ry measures shou ld be s t r e s s e d when f o l - l o w i n g t h e procedures o f t h e o f f i c e . Con tac t w i t h mercury shou ld be avoided bo th i n h a n d l i n g mercury and from b r e a t h i n g i t s vapors. S a l t s o f mercury o r s o l u t i o n s c o n t a i n i n g mercury which con tac t t he s k i n should be washed away immediately w i t h soap and water.

3. V e n t i l a t i o n i s impor tan t , s i n c e keep ing areas v e n t i l a t e d by t h e use o f e x h a u s t fans can draw t h e a i r away f r o m t h e o p e r a t o r . One should avo id work ing i n over-heated rooms, i.e., above 75' F. The amal- gamator should be k e p t away from r a d i a t o r s and heaters.

4. The f l o o r s should be non-porous and f r e e from cracks, i n o rder t o p rec lude t h e h a r b o r i n g o f s p i l l e d mercury, and every p recau t ion shou ld be exe rc i sed t o p reven t s p i l l i n g mercury. C lean ing o f f l o o r s and tops o f cab ine ts and workbenches w i t h a depressant o f vapors, such as ca l c ium p o l y s u l f i d e a p p l i e d i n accordance w i t h t h e manu fac tu re r ' s d i r e c t i o n s , should be i n s t i t u t e d .

5. Teaching personne l t o rep lace t h e c l e a n i n g equipment r e g u l a r l y and t o change wash and r i n s e w a t e r f r e q u e n t l y s h o u l d be h e l p f u l .

SUMMARY

2.

To summarize t h i s survey o f t h e l i t e r a t u r e , i t may be sa id , i n o rde r t o p r e s e n t an e v a l u a t i o n o f t h e r o l e o f mercury as an e n v i r o n m e n t a l hazard t o h e a l t h o f t h e d e n t a l o f f i c e w i t h o u t a wearisome e x c u r s i o n t h r o u g h t h e a c c u m u l a t i o n o f r e p o r t s and impress ions wh ich have been c i t e d t o a f f i r m t h e r e l a t i o n s h i p , a few c r i t i c a l a p p r a i s a l s by s c i e n - t i f i c i n v e s t i g a t o r s have been b r i e f e d . Ev idence was found t h a t t h e amount o f v a p o r i z e d mercury i n t h e d e n t a l o f f i c e i s g r e a t e s t d u r i n g h a n d l i n g o r heat ing , o r when t h e mercury i s l e f t unattended. A rev iew o f t h e l i t e r a t u r e shows t h a t t h e e f f e c t s o f exposure t o vapor i zed mer- c u r y i n a d e n t a l o f f i c e have been w e l l documented. P o t e n t i a l hazards such as a l l e r g i c m a n i f e s t a t i o n s , and some o r a l and sys temic d i s o r d e r s may r e s u l t f rom occupat iona l exposure t o vapor ized mercury.

Occupat iona l exposure f rom vapor i zed mercury shou ld n o t exceed 0.1 m i l l i g r a m per c u b i c meter o f a i r per e i g h t hou r day i n o r d e r t o a v o i d

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damage. I n l i g h t o f p resen t knowledge, t h i s amount o f exposure i s n o t expec ted t o cause any d e t e c t a b l e harm a t any t i m e d u r i n g l i f e . There i s no reason, however, why a l l p o s s i b l e means t o reduce occupat iona l ex- posure below t h i s l i m i t should n o t be employed i f they a r e f e a s i b l e from t h e s t a n d p o i n t o f expense and p h y s i c a l arrangement o f t he d e n t a l s u i t e . The d e n t i s t has t h e r e s p o n s i b i l i t y t o h i s s t a f f and h i m s e l f t o reduce occupat iona l exposure t o vapor ized mercury t o the minimum.

Perhaps one may summarize f r o m t h i s r e v i e w by q u o t i n g Frykho lm, P ro fesso r o f Opera t i ve D e n t i s t r y , The Royal School o f D e n t i s t r y , Stock- holm, r e g a r d i n g t h e importance o f mercury as a poisonous hazard i n the den ta l o f f i c e . Frykholm s t a t e s , "There i s a h e a l t h r i s k involved, which should n o t be exaggerated no r neglected."

C O N C L U S I O N S

I. The e x t e n t o f exposure i n most d e n t a l o f f i c e s may be s u f f i c i e n t t o b r i n g about many a l l e r g i c man i fes ta t i ons i n d e n t a l personnel who a r e s e n s i t i v e t o m e r c u r y ;

2. S ince mercury i s used f r e q u e n t l y by genera l p r a c t i t i o n e r s , ex- treme c a r e shou ld be used by t h e p r o f e s s i o n i n t h e h a n d l i n g and use of t h i s ma te r ia l ;

3. A i r b o r n e con tamina t ion occurs as t h e r e s u l t o f t h e v a p o r i z a t i o n of t he mercury s to red , s p i l l e d , o r d iscarded i n the o f f i c e ;

4. D i r e c t h a n d l i n g o f mercury o r i t s compounds shou ld be avoided.

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"The rule o f clearness is not to write so that the reader can understand, but so that he cannot possibly misunderstand!'

CHRISTOPHER MORLEY

CHARLES F. KETTERING:

"In research one needs a lot of intelligent ignorance; un- intelligent motion is more important than intelligent stand- ing still.11