CLEARANCE HALF-LIFE OF MERCURY IN URINE AFTER THE CESSATION OF LONG-TERM OCCUPATIONAL EXPOSURE - INFLUENCE OF A CHELATING AGENT (DMPS) ON EXCRETION OF MERCURY IN URINE

The elimination of mercury (Hg) in urine was investigated in 12 former chloralkali workers exposed to metallic Hg vapour for two to 18 (median five) years. Morning urine samples were taken on several (median 9) occasions after change of employment or retirement, The median follow up time was 28 months. The decrease in concentration of Hg in urine (U-Hg) was well characterised by a one compartment model. Three different regression methods were used; non-linear least squares regression (NLSR), weighted non-linear least squares regression (WNLSR), and linear least squares regression (LLSR) after log transformation of the U-Hg data. The median half Life from the WNLSR method was 55 days. There were no large differences in the half Life estimates given by the WNLSR or the NLSR methods, but for five subjects the LLSR method gave poor fits. There was a non-significant tendency towards longer half lives with higher initial U-Hg. About three years after the cessation of occupational exposure a mobilisation test with 2,3-dimercaptopropane-1-sulphonate (DMPS) was performed on seven subjects. Excretion of Hg, copper (Cu), and zinc (Zn) in urine was estimated before and after the ingestion of 300 mg of DMPS. Treatment with DMPS increased 24 hour urinary excretion by a factor of 7.6 for Hg, 12 for Cu, and 1.5 for Zn. The relative increase in U-Hg was not significantly higher than that obtained in a previous study of an occupationally unexposed group. A major proportion (62%) of Hg excreted during 24 hours after DMPS appeared in the first six hours. For Hg and Zn, but not for Cu, the amounts excreted before and after DMPS were highly correlated. The excretion of Hg in urine probably reflects the amount of Hg stored in the kidneys; and the use of a single dose of DMPS gives no further information about the size of that pool.