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Forty-seven chloralkali workers exposed to mercury vapour for an average of 13.3 years were compared with 47 referents matched for age in a cross-sectional study of thyroid function. The mean urinary mercury concentration in the exposed workers was low compared with other studies of chloralkali workers: 5.9 nmol mmol-1 creatinine (range 1.1-16.8) vs 1.3 nmol mmol-1 creatinine (range 0.2-5.0) in the reference group. The median serum concentration of reverse triiodothyronine (rT3) was statistically significantly higher in the exposed subjects compared with the referents (268 pmol l (-1) and range 161-422 vs 240 pmol l(-1) and range 129-352; P = 0.009). The difference between the exposed subjects and the referents was most pronounced in the highest exposed sub-groups. The free thyroxine (T4)/free T3 ratio was also higher in the highest exposed subgroups compared with the referents. The median serum concentration of tumour necrosis factor alpha (TNF-alpha) was lower in the exposed subjects (7.3 pg ml(-1) and range 4.4-69.7 vs 8.0 pg ml(-1) and range 6.0-34.6; P = 0.004). Exposed subjects with the lowest urinary iodine (<67.8 nmol mmol(-1) Cr) had higher serum concentrations of reverse T 3 and a higher free T4/free T3 ratio than the other subjects, suggesting that a low concentration of iodine in urine may be a risk factor for increased serum concentrations of reverse T3 and the free T4/free T3 ratio in subjects exposed occupationally to mercury vapour. The study could indicate a slight effect of low mercury vapour exposure on the function of the enzyme type I iodothyronine deiodinase, possibly modified by comparatively low urinary iodine concentrations., (Copyright 2000 John Wiley & Sons, Ltd.)

The object of this work was to investigate possible interactions of mercury, cadmium and selenium in humans. Selenium and cadmium in blood and urine were determined in this cross-sectional study of 130 males, of whom 77 had been previously exposed to mercury vapour at a chloralkali plant. Of the participants, 61.5% were smokers and 16.2% were never-smokers. The concentration of selenium in blood (B-Se) was significantly lower in subjects currently smoking more than 50 g of tobacco per week compared to never-smokers, whereas the concentration of cadmium in blood (B-Cd) was significantly higher in all categories of current smokers. In the multiple linear regression analysis, B-Se as a dependent variable was negatively associated with B-Cd, whereas current smoking habits were not included in the model as a predictor variable. In contrast, B-Cd as a dependent variable was positively associated with current as well as previous smoking habits, and negatively with both B-Se and the 'cumulative dose' of previous mercury vapour exposure. The concentration of selenium in blood was also negatively associated with B-Cd in the group of never-smokers (Spearman's r = -0.80; P < 0.001). In conclusion, these results suggest a depressive effect of cadmium on the concentration of selenium in blood, while smoking alone did not operate as a true predictor for this effect. Furthermore, previous exposure to mercury apparently modifies the concentration of cadmium in blood.

Urinary selenium excretion was studied in 21 mercury vapour (Hgo)-exposed workers involved in the demolition of a chloralkali plant. The subjects had no known previous occupational exposure to mercury. Their mean pre-exposure urinary mercury concentration, determined on average 1.2 days prior to the exposure, was 0.8 nmol mmol-1 creatinine (range 0.3-1.9). Their last mean urinary mercury concentration, determined on average after 51.4 days (range 19-103) of exposure, was 4.8 nmol mmol-1 creatinine (range 1.2-10.0). The exposure ceased on average 4.1 days after the last determined urinary mercury concentration. The corresponding concentrations of urinary selenium decreased from an average of 39.1 nmol mmol-1 creatinine (range 13.9-89.5) to 29.0 nmol mmol-1 creatinine (range 10.1-52.9) (P = 0.002). This finding may indicate that even a low to moderate work-related exposure to Hgo may reduce the urinary selenium concentration in humans in a manner that is not yet fully known.