Biological monitoring of exposure to metallic mercury.

The concentration of mercury was analysed in 418 paired blood and urine samples from 185 workers at three chlorine-alkali plants. The correlation between the concentration of mercury in blood and urine and their dependence on age were examined. There is a considerably larger variability of the mercury levels in urine than in blood. In more than 90% of paired samples, the mercury concentration was higher in urine than in blood. The ratio between the mercury concentration in blood and urine tends to increase with age indicating a weak tendency to age-correlated reduction of renal mercury excretion. As an indicator of exposure to mercury vapour, the mercury content of blood is preferable to that of urine. Active control measures are recommended when the mercury content of blood exceeds 150 nmol/l. When the blood level exceeds 300 nmol/l occupational mercury exposure ought to be stopped until the level has decreased to below 100 nmol/l.