Pharmacokinetics of mercury from dental amalgam

Abstract

The overall aim of the present work has been to obtain quantitative and qualitative data on mercury from dental amalgam in humans. The influence of amalgam removal on mercury levels in blood, plasma and urine has been studied in twelve volunteers. All amalgam fillings were removed during one dental session. A transient increase of mercury in blood and plasma was observed within 48 h after amalgam removal, and sixty days after the mercury levels in all media had decreased to about 60% of the pre removal levels. A bi-exponential model was applied on mercury in plasma with the median half-time of the second phase being 88 days. The kinetics of mercury in urine was fitted to a mono-exponential model, the median half-time being 46 days.

The pharmacokinetics of mercury vapor was studied after a single dose exposure in human volunteers. Nine subjects were exposed to 400 µg/m3 mercury vapor for15 min. The retention was on average 67% of the inhaled mercury dose. A rapid absorption phase was seen in blood and plasma, followed by a bi-exponential decline. In plasma the median half-time of the second phase was 10 days with a large inter-individual variation. The estimated total amount of mercury excreted via urine during 30 daysranged from 8% to 41%.

Mercury levels in saliva and feces before and after amalgam removal were studied. The fecal mercury concentrations were more than ten times higher in the pre-removal samples than those found in a reference group with no amalgam fillings. Two days after removal, the fecal mercury concentrations increased about 100 times, followed by a significant decrease. Sixty days after amalgam removal, the mercury levels in feces were still slightly higher than in the reference group. In saliva the median mercury levels declined from the pre-removal level of 200 nmol/kg to 1 nmol/kg sixtydays after amalgam removal.

The kidney is a target organ for inorganic mercury and in animal studies decreased renal function has been shown after placement of amalgam fillings. The mercury levels in blood, plasma and urine and the kidney function were studied before and after amalgam removal. A number of sensitive renal parameters were determined: the glomerular filtration rate (GFR) and the excretion of N-acetyl-ß glucose aminidase (NAG), ß2-microglobuline and albumin. No signs of kidney dysfunction were detectable.

Effects on mercury levels in blood, plasma and urine after 14-days treatment with a chelating agent (DMSA) or placebo were studied in twenty subjects, relating their symptoms to mercury exposure from amalgam fillings. In addition, these effects were related to possible changes of symptoms. Three cases of generalized hypersensitive reactions were encountered at the end of the treatment period. A significant increase in urinary mercury excretion was apparent during DMSA treatment, and the blood mercury levels decreased. There was no evidence that chelating therapy alleviated symptoms allegedly attributable to mercury from amalgam fillings.

In summary, amalgam fillings constitute a significant source of exposure to mercury. Mercury levels in blood, plasma, urine, saliva and feces decrease considerably after the removal of dental amalgam. No adverse effects on the kidney function were observed from the mercury exposure in conjunction with amalgam removal. DMSA treatment appears to mainly affect the mercury excretion from the kidney, and the risk of hypersensitivity reactions is considerable during prolonged treatment. Combined evaluation of the decline of mercury in plasma after amalgam removal and after the single dose exposure clearly verifies the pharmacokinetics of mercury as at least tri-exponential. The pharmacokinetic analysis of mercury verifies the daily mercury dose in subjects with an average number of amalgam fillings to be 5-9 µg per day.