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J. M. HARRINGTON T.U.C. Centenary Institute of Occupational Health, London School of Hygiene and Tropical Medicine, London WC1 7HT

Markedly increased

levels of environmental mercury, discovered by chance in a commercial laboratory using volumetric gasanalysis techniques, were associated with dangerously high levels of urinary mercury in the laboratory technicians. Although urinary concentrations are a poor guide to clinical mercury poisoning, they rapidly detect high body concentrations. The hazard arose through poor laboratory technique and ignorance of the dangers of mercury. Similar circumstances are common in hospital practice. The belief that mercury is a harmless material persists, and people who work with mercury must be made aware of the risks involved in handling the element.

Sum ary


MERCURY has been recognised as a hazardous element for 3500 years. Occupationally acquired mercurial poisoning occurred in mining processes in the 16th century, and Ramazzini graphically described the plight of the mirror silverers on the island of Murano in the Venetian lagoon.1 Nevertheless, the risk of mercury poisoning continues despite legislative attempts at control over the past seventy-four years. The present report highlights the continuing and potentially dangerous risk of mercury intoxication present during the routine measurement of carbon dioxide in fluids by volumetric gas analysis. This particular hazard was noted when the attention of a company medical officer was drawn to a small qualitycontrol laboratory employing two female laboratory assistants. They complained that they were unable to wear gold or silver jewellery on their hands because it became " silvered MATERIALS


feet’ and the ambient temperature was in excess of 23 °C, with poor ventilation. The Martin apparatus was in use and droplets of mercury were visible on the bench, the floor, and in the sink. The pockets and shoes of the laboratory staff also contained mercury. Under ideal circumstances, the Martin apparatus can be used without spillage of mercury, but in this laboratory the technique used by the laboratory assistants was faulty. Vigorous raising and lowering of the reservoir can produce a fountain of mercury, which spills over the top of the glass lip. In addition, expulsion of the test liquid through the side arm of the tap at the end of the measurement often carries with it some mercury. The speed with which the technicians undertook serial analyses was so fast that mercury was lost during most measurements. The concentration of mercury in the room exceeded 750 /g. per cubic metre, and air removed from the room by an extraction fan above breathing level contained between 550 and 650 /.g. per cubic metre. These values are more than 15 and 12 times the current threshold limit value, respectively.3 Urinary mercury measurements made on specimens passed by the two technicians on the day after the environmental readings were 1150 and 425 g. per


Mercury is widely used in apparatus for analysing gas in liquids. The Van Slyke, Haldane, and Martin apparatuses are

commonly used in hospitals.


apparatus was designed to measure the carbon-dioxide content of beer. Mercury in the reservoir is covered by a thin layer of water, the corresponding mercury level on the other side being enclosed by the Under normal working test fluid or the tap at the top. conditions, no mercury is exposed to the atmosphere and none is spilt. In practice, this proves to be far from the case.

Airborne mercury concentrations in the laboratory were measured using the Hendry mercury-vapour meter calibrated and zeroed on site. The instrument has a lower limit of detection of about 7 Ag. per cubic metre of air and a precision of 4 Ag. per cubic metre. RESULTS




of the



7t X 13 X 10


(}lg.per litre).

mercury levels in laboratory technicians using Martin’s apparatus. First measurements taken in 130 staff from twenty laboratories.


Numbers indicate technicians who had either an initial or serial urinary mercury measurement which exceeded 100 g. per litre. * Techniciar. for whom serial measurements were not available.


litre. Repeat readings two weeks later showed levels of 2400 and 203 j1.g. per litre, respectively. All measurements were corrected to standard urine density of 1.016 g. per ml. Subsequent detailed clinical examination of both laboratory assistants revealed no evidence of chronic mercurialism and there was no glycosuria or proteinuria. As a result of these findings, the laboratory was closed and the technicians removed from exposure. The laboratory was stripped down and the floor taken up. Pools of mercury were discovered under the floor boards, and the whole room was redecorated and an impervious floor laid. Repeat environmental readings after rebuilding showed mercury levels below 20 g. per cubic metre of air. The technicians’ mercury excretion fell over the next three months to 119 and 111 }.Lg. per litre, respectively (see accompanying

table). All the companies in the group were informed of the mercury hazard and a survey of urinary mercury measurements of all 130 staff from twenty laboratories started (see accompanying figure). was High excretion of mercury (i.e., more than 100 jug. per litre) was followed up with serial measurement over several months (see table). Subjects 1 and 2 have been described earlier in the text, and the excretionrates illustrate the effect of removing them from their contaminated laboratory. No specific treatment was given. Subjects 3, 4, 5, and 6 work in laboratories elsewhere and results illustrate the effect of improved handling procedure and hygiene in the laboratory. Subject 5 demonstrated an initial rise in excretion, and this laboratory is being redesigned. There was one other technician whose level exceeded 100 jug. per litre (110 g. per litre). Serial measurements were not available. None of the 130 subjects demonstrated any signs of clinical mercurialism. Environmental and urinary levels are now mercury regularly measured. These with precautions, together overhauling the laboratories, should effectively eliminate the risk, provided that the technicians are trained to use the apparatus correctly. In one laboratory, 7 lb. of metallic mercury An imwas recovered from under the floor boards. pervious floor has been laid to prevent this occurring in the future. DISCUSSION

vapour pressure detectable at low as —12°C. Pools of mercury temperatures to exposed temperatures of 25°C in an enclosed room produce mercury concentrations in air of 3 mg. per cubic metre. The level in the laboratory atmosphere was dangerously high and the high mercury excretion by the staff also warranted urgent action. The correlation between urinary mercury levels and symptoms of mercury poisoning is rather poor 5; but in a study of 83 men exposed to mercury,6 18 of whom had clinical evidence of mercury poisoning, all the affected workers had urinary mercury concentrations in excess of 300 Ag. per litre, although some symptomfree workers had levels of 1000 g. per litre. Clearly there is wide variation in tolerance to mercury. A study of scientific-glassware manufacturers revealed symptom-free workers excreting up to 2200 u.g. per litre.’ However, in a survey of laboratory technicians





exposed to moderate levels of mercury over several years,8 there was a significant correlation between urinary and airborne mercury (r=0-47). As a result, Lauwerys and Buchet suggested a maximum allowable urinary mercury excretion of 50 pg. per litre. If levels rise above this, measures must be taken to reduce environmental contamination. The use of a personal sampling device may be a more accurate method of determining individual exposure to mercury vapour and seems to correlate better with urinary mercury excretion.9.lo Nevertheless, excretion-rates do not give a clear picture of how hazardous the element is to a given individual. None of the 130 employees in the present study showed any signs of chronic mercurialism, yet 20 of them (14%) excreted more than 50 /g. of mercury per litre of urine. Biological monitoring should only be used as the prime indicator of control measures if no better method is available. Mercury-in-air monitoring is to be preferred, since it is not only more accurate but it is also not subject to the variation inherent in measuring an individual’s response to a body burden of mercury. The second feature of the present investigation was the workers’ total ignorance of the potential danger. Presumably the message has not been made Merclear enough or emphasised often enough. curialism still occurs and is nearly always due, in industrial practice, to bad handling and ignorance of the risks. Enclosure of the apparatus is one way of reducing the risk, or alternative methods of gas analysis could be used. The manometric adaptation of the Martin apparatus 11 eliminates the risk of poisoning, since the mercury is completely enclosed. Workers exposed to a potential mercury risk should be examined clinically at regular intervals, preferably every six months.12 At this examination the urine should be examined for proteinuria and a handwriting test performed. The risk of renal damage means that any mercury worker with proteinuria should be removed from exposure, but even severe renal damage appears to be reversible in some reported cases.13 Whereas lead and arsenic are well-established in the minds of workers as dangerous elements, mercury is persistently ignored as a hazard. There is little doubt that the circumstances described in industry occur equally commonly in hospital laboratory practice, especially if the gas-analysis apparatus is used by clinical staff in a side room off the ward. REFERENCES

Ramazzini, B. De Morbis Artificium (translated by C. Wright). Chicago, 1940. 2. Martin, E. C. J. Inst. Brew. 1936, 79, 10. 3. Technical Data Note 21 (Rev.). Department of Employment. H.M. Stationery Office, 1973. 4. Noe, F. E. New Engl. J. Med. 1959, 261, 1002. 5. Ladd, A. C., Zuskin, E., Valic, F., Almonte, J. B., Gonzales, T. V. J. occup. Med. 1966, 8, 127. 6. Rentos, P. G., Seligman, F. J. Archs envir. Hlth, 1968, 16, 794. 7. Danziger, S. J., Possick, P. A. J. occup. Med. 1973, 15, 15. 8. Lauwerys, R. R., Buchet, J. P. Archs envir. Hlth, 1973, 27, 65. 9. Bell, Z. G., Wood, M. W., Kuryla, L. A. J. occup. Med. 1973, 15, 340, 420. 10. Bell, Z. G., Lovejoy, H. B., Vizena, T. R. ibid. p. 501. 11. Bayles, P. F., Brown, D. G. W., Martin, P. A. Proc. Am. Soc. Brew. Chem. 1968, 21, 43. 12. Duffield, D. P. Chem. Ind. 1968, 197. 13. Kazantzis, G. Trans. Soc. occup. Med. 1970, 20, 54. 1.