Industrial Health, 1996, 34, 421-425 421 Blood Mercury in Workers Exposed to the Preparation of Mercury Cadmium Telluride Layers on Cadmium Telluride Base Abstract: Study was conducted in a group of 32 persons engaged in liquid phase epitaxial growth of mercury cadmium telluride (MCT) layers for nearly 11 years. Airborne mercury concentrations in work environment have been exceeding the threshold limit value of 0.05 mg/m' recommended by ACGIH". Hg concentration in workplace during peak working hours remained between 0.04-0.08 mg/m;. Findings were compared with 32 unexposed referents. Mercury value was estimated 1.60 ± 0.20 (mean ± SD) in control, and in Phase I and II, 10.72 ± 1.34 ng Hg/ml and 8.08 ± 1.15 ng Hg/ml of blood respectively. Results indicate a fall in blood mercury level during the second phase of study. But the values did not return to normal even after a gap of 3 months. An individual who met with a mercury accident showed 226 ng Hg/ml of blood which decreased to 25 ng/ ml after 3 months. It is inferred from the present study that Hg level has increased significantly in MCT workers during working period, and also in non-working period, the values were higher than controls. Key words: Mercury cadmium telluride - Industrial exposure to mercury - Airborne mercury concentration - Accidental exposure - Mercury in blood Mercury is a heavy metal which is ubiquitous in biosphere, environmentally stable, shows strong affinity for biological tissues and so far has not been demonstrated to have any beneficial function in humans' ~'. Elimination of Hg from the body is biphasic depending upon short term and long term occupational exposure4' ~'. The half life reported is about 3 days for the fast phase and 15-30 days for the slow phase''''. A tracer study has indicated half life of 49-164 days'. Studies on mercury and selenium in workers exposed in chloralkali plants9 and acute mercury poisoning in humans due to mercury vapor release from smelting alloys have indicated an increase in blood mercury level due to long term exposure'. In MCT project, mercury cadmium telluride layers of 10 mm x 10 mm x 1 mm -15 mm x 15 mm x 1 mm size are grown on cadmium telluride base. A process completes in two stages: layer preparation and layer characterization. During the layer preparation Hg is dissolved in cadmium telluride solution at 600 C. Layers are grown at 500 C in a high pressure liquid phase epitaxi reactor. The stage of the process takes two days. In the layer characterization exposure to mercury is negligible in comparison to the layer preparation. Address for Correspondence: Dr, Manju GUPTA, Scientist, Institute of Nuclear Medicine and Allied Sciences, Lucknow road, Delhi-110054, India
422 M. GUPTA et al. The aim of the present study is to estimate the level of mercury in blood of persons exposed occupationally to the preparation of MCT layers for nearly 11 years. Blood samples were collected from a group of 32 persons working with the MCT project for the last 11 years. Workers' mean age was 42.34 ± 9.07 years (± SD). The study was divided into two major groups, phase I and phase II. Phase I study was conducted when the project was on smooth run and mercury was handled on every working day. Because of some technical faults work of the layer preparation was hampered for 3 months but the layer characterization continued. During this period blood samples were collected for phase II study. Thirty-two referents of ages 40.5 ± 6.80 years (mean ± SD) were chosen for comparative study. Different groups were described as follows: Phase I - A group of 32 persons engaged in MCT project. Phase II - 3 months gap study with the same individuals as in phase I. A - Direct handling of mercury (group of 12 persons). B - Staying in same vicinity, never handled with mercury. C - Same as in group A but after 3 months. D - Same as in group B but after 3 months. Blood samples were collected in heparinized tubes. Digestion was done in a mixture of HCLO4-H,SO4-HNO3 (1:1:3) at 60 C and continued till organic matter was broken up and clear solution was obtained. Analysis of samples was performed by cold vapor atomic absorption technique, using a Perkin Elmer Atomic Absorption Spectrophotometer model 3110 (USA) with detection limit of 2 nmol Hg/liter. Reproducibility and accuracy of the chemical analysis was tested in two ways: by adding a known solution of mercury salt in water and blood. In this method accuracy was found acceptable, though precision for different media and concentration varied. In external reference material blood for mercury, obtained from Behring Institute, Germany, showed 97% of the recommended values of reference material in our estimation. Air sampling was done from time to time by project staff using JEROME 43 x mercury vapor analyzer with detection limit of 0.001 mg/m3. Samples were collected in working and non-working periods. Readings were taken from the working room of reactor area and the adjacent places. Data were analyzed statistically by applying paired and unpaired Student t-test. Values of significance were expressed in terms of p < 0.01 and p < 0.001. In a group of 32 persons, an individual while working met with a mercury accident (a mercury container was broken and large amount of mercury got spilled over the floor). His sample monitored after 24 hours of the accident showed 226 ng Hg/ml of blood. After 3 months his Hg level was found to decrease remarkably to a level of 25 ng Hg/ml of blood. Clinical investigations viz., ECG, X- ray, blood biochemistry and urine analysis were done immediately after the accident and at an interval of 3 months. Findings did not reveal any clinical changes. Apparently he did not develop any health complications after the accident except
BLOOD MERCURY IN Hg-Cd-Te WORKERS 423 minor mercury burns, headache and nausea which got subsided later. No chronic respiratory disorder was noticed, though mercury was reported to cause chest pain, dyspnea, coughing, haemoptysis and interstitial pneumonitis besides nervous system disorders after chronic exposure10'. Air sampling in project premises indicated increased levels of Hg in air. In close vicinity of the reactor during peak working hours Hg concentration was found between 0.04-0.08 mg/m:3, occasionally reached to 0.100 mg/m3. In adjacent areas during working period, Hg range was between 0.001-0.005 with 0.003 ± 0.001 mg/ m3 (mean ± SD). Survey in non-handling period also indicated some traces of mercury (0.001 mg/m3) but at rare incidences only. Figure l shows blood mercury levels in different groups of MCT workers. Number of subjects is shown in parenthesis. Blood Hg levels in non-mercuryhandling groups (B&D) were always lower than mercury-handling groups (A&C) but significantly higher than the referent group. Fig. 1. Blood mercury levels in MCT workers (Each Column with vertical bar indicate ng Hg/ml of blood (mean ± SE)). Number of subjects are shown in parenthesis. Horizontal bars with single and double asterisks indicate significant differences at p < 0.01 and p < 0.001, respectively. Phase I - Working with mercury; Phase II - 3 months gap study, A - Working directly with mercury. B - Never handled mercury but working in same project. C - Group A individuals after three months. D - Group B individuals after three months.
424 M. GUPTA et at. The present study has demonstrated that in most of the groups differences in blood mercury concentration were highly significant (P < 0.001). The Study conducted after 3 months indicated a drop in mercury level in case of all the individuals. Earlier studies4-'' have reported that the half life of metallic Hg is about 40-60 days when major part of Hg burden is eliminated. But mercury level in the present study did not return to a normal range even after a gap of 3 months. One of the possible explanations for non return of blood mercury level to the normal range even after 90 days could be the regular exposure of staff to mercury contaminated air as indicated in air survey. During peak working hours airborne Hg concentrations in work place always exceeded the threshold limit value of 0.05 mgl m3 recommended by ACGIH''. In mercury non-handling period Hg level in work place was recorded though at very low concentration. Enhanced Hg concentration in non-mercury-handling staff (groups B&D) as they were staying in the same vicinity favors contamination of air with mercury. Other reasons for raised mercury level could be that either use of mercury was not stopped completely (characterization of layer continued) though reduced significantly or elimination of mercury from the body might have been delayed. A tracer study favors the delay in excretion of mercury (49-164 days) from the body5'. Though further studies are needed to conclude but assumptions on an increase in base line mercury level due to very long and low exposure can not be ignored. Literature favoring the view could not be cited. This study reveals that blood Hg during working period in MCT workers was high as compared to controls and continued to show high level in that period when major work was stopped. REFERENCES 1) American conference of Governmental Industrial Hygienists: TLVs and biological exposure indices, Cincinnati, 1993-1994 American Conference on Industrial Hygienists. 2) Oehme FW. Persistence Versus Perseverance FW Oehme Eds In: Toxicity of heavy metals in environment. Part I, Dekkar, New York/Basel. 1978: 1-2. 3) Oehme FW. Mechanism of heavy metal inorganic toxicities. IN: FW Oheme Eds. Toxicity of heavy metals in the environment DEKKAR, New York. 1978; 69-85 Part I. 4) Skare I, Enqvist A. Urinary mercury clearance of dental personnel after long term intermission in occupational exposure. Swed Dent J 1990; 14: 255-9. 5) Roles HA, Boeckx M, Ceulemans E, Lauwerys RR. Urinary excretion of mercury after occupational exposure to mercury vapor and influence of the chelating agent meso-2,3- dimercaptosuccinic acid (DMSA). Br J Ind Med 1991; 48: 247-53. 6) Clarkson TW, Hursch JB, Sager PR, Syversen TLM. In: Clarkson TW, Friberg L, Nordberg GF, Sager PR Eds. Biological monitoring of toxic metals. New York: Plenum press, 1988; 199-245. 7) Barregard. L, Sallsten G, Schutz A, Attewell R, Skerfving S, Jarvholm B. Kinetics of mercury in blood and urine after brief occupational exposure. Arch Environ Health 1992; 47: 176-84. 8) Houeto P, Sandouk P, Baud F, Levillain P. Elemental mercury vapor toxicol; treatment and levels in plasma and urine. Hum Exp Toxicol 1994; 13: 848-52.
BLOOD MERCURY IN Hg-Cd-Te WORKERS 425 9) Ellingsen G, Holland I, Thomassen Y, Landro-Olstad M, Frech W. Mercury and selenium in workers previously exposed to mercury vapor at a chloralkali plant. Br J Ind Med 1993; 50: 745-52. 10) WHO. Environmental health criteria 118: Inorganic mercury, Geneva, World Health Organization 1991; 19-20. Institute of Nuclear Medicine and Allied Sciences, Lucknow road, Delhi-110054, India Manju GUPTA, Jai Krishna BANSAL and Chandra Mohan KHANNA (Received November 28, 1995 and in revised form May 2, 1996)