MERCURY IN BIOLOGICAL-FLUIDS AFTER AMALGAM REMOVAL

Dental amalgam is the major source of inorganic mercury (Hg) exposure in the general population. The objective of the present study was to o btain data on changes in Hg levels in blood, plasma, and urine followi ng removal of all amalgam fillings during one dental session in 12 hea lthy subjects. The mean number of amalgam surfaces was 18 (range, 13 t o 34). Frequent blood sampling and 24-hour urine collections were perf ormed up to 115 days after amalgam removal, and in eight subjects addi tional samples of plasma and urine were collected up to three years af ter amalgam removal. A transient increase of Hg concentrations in bloo d and plasma was observed within 48 hours after amalgam removal. In pl asma, the peak concentrations significantly exceeded the pre-removal p lasma Hg levels by, on average, 32% (1.3 nmol/L; range, 0.1 to 4.2). N o increase in the urinary Hg excretion rate was apparent after amalgam removal. An exponential decline of Hg was seen in all media. Sixty da ys after the amalgam removal, the Hg levels in blood, plasma, and urin e had declined to approximately 60% of the pre-removal levels. In seve n subjects, who were followed for up to three years, the half-lives of Hg in plasma and urine were calculated. In plasma, a bi-exponential m odel was applied, and the half-life was estimated at median 88 days (r ange, 21 to 121). The kinetics of Hg in urine (nmol/24 hrs) fit a mono -exponential model with a median half-life of 46 days (range, 35 to 67 ). It is concluded that the process of removing amalgam fillings can h ave a considerable impact on Hg levels in biological fluids. After rem oval, there was a considerable decline in the Hg levels of blood, plas ma, and urine, which slowly approached those of subjects without any h istory of amalgam fillings.