revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 442
5. POTENTIAL FOR HUMAN EXPOSURE
uptake is still below the dose corresponding to the acceptable daily intake (ADI) of mercury. The ADI of
40 µg total mercury, 30 µg of which are allowed for methylmercury, results in a total dose of approximately
30 µg after accounting for absorption (Halbach 1994; WHO 1976). WHO (1990) estimates a daily
absorption of 2.61 µg from background exposure for persons without amalgam exposure.
In a recent study by Schweinsberg (1994), the author monitored mercury in blood, urine, and hair of
subjects with amalgam fillings, in subjects who consumed fish, and in mercury-exposed workers. With
respect to hair concentrations, the author reported a mean mercury level in hair of 560 µg/kg (ppb),
940 µg/kg, and 1,600 µg/kg in subjects that consumed the following mean amounts of fish per month:
120 g/month (range, 0–6 dental amalgams, 2.56±2.123 µg/L for persons with fish consumption >990 g/month
and no dental amalgams, and 2.852±2.363 µg/l for persons with fish consumption >990 g/month and
>6 dental amalgams. Mercury concentrations in the urine of occupationally exposed thermometer factory
workers were higher, by a factor of 100, than in the group with amalgam fillings. The author concluded
that both amalgam fillings and the consumption of fish burden individuals with mercury in approximately
the same order of magnitude.
In a more recent study of lactating women, Oskarsson et al. (1996) assessed the total and inorganic mercury
content in breast milk and blood in relation to fish consumption and amalgam fillings. The total mercury
concentrations (mean±standard deviation) in breast milk, blood, and hair samples collected 6 weeks after
delivery from 30 Swedish women were 0.6±0.4 ng/g (ppb), 2.3±1.0 ng/g, and 0.28±0.16 µg/g, respectively.
In milk, an average of 51% of total mercury was in the inorganic form, whereas in blood an average of only
26% was in the inorganic form. Total and inorganic mercury levels in blood and milk were correlated with
the number of amalgam fillings. The concentrations of total mercury and organic mercury in blood and total
mercury in hair were correlated with the estimated recent exposure to methylmercury via consumption of
fish. There was no significant difference between the milk levels of mercury in any form and the estimated
methylmercury intake. A significant correlation was found, however, between the levels of total mercury in
blood and in milk, with milk levels being an average of 27% of the blood levels. There was also an
association between inorganic mercury in blood and in milk; the average level of inorganic mercury in milk
was 55% of the level of inorganic mercury in blood. No significant correlations were found between the
levels of any form of mercury in milk and the levels of organic mercury in blood. The results indicated that