No. 104 - Miljøstyrelsen

A recent study with rats showed an interplay between mercury vapour and
methyl mercury and the resulting level of mercury in the brain of offspring.
Low dietary exposure to methyl mercury and parallel exposure to mercury
vapour increased the level of mercury in the brain of offspring. Thus, the
study concluded that human foetus exposed to both methyl mercury and
mercury vapour has increased risk of impaired neurodevelopment compared
with exposure to the two forms of mercury separately (Ishitobi et al., 2010).
Body half-life of mercury after exposure to mercury vapour is 35-90 days
(WHO 1980). Retention in the brain is however somewhat longer. Mercury is
particularly long-term accumulated in the kidneys.
Metallic mercury is excreted in exhaled air, sweat and saliva. After conversion
to mercury(II) compounds these species may be excreted in urine through the
kidneys (Berlin 1977).
4.3 Human intake of mercury
The predominant route of exposure to mercury for the general public is
through food, especially from fish and other seafood. The daily average intake
through food is estimated at 2-3 �g mercury – almost exclusively in the form
of methyl mercury (see Table 4-1). This is an organic form of mercury, which
can be formed by micro-organisms in the aquatic environment, and which has
a particular tendency to accumulate in aquatic food chains. Methyl mercury
can just as mercury vapours be transported easily and readily across the
blood-brain and the placental barriers – and is thereby similarly problematic.
For methyl mercury a ”secure” limit value has been set at a daily intake of 0.1
�g Hg/kg body weight. (Clarkson et al., 2003).
An additional contribution of mercury may origin from dental amalgam
fillings, which contains around 50 % of mercury. It is estimated that 0.2 �g
mercury is released from each amalgam filling per day (Richardson et al.,
2009). WHO estimates that the ”intake” from dental fillings may amount to
between 1.2 and 27 �g mercury per day (Holmes et al., 2009), but that the
absorption in the gastrointestinal tract as mentioned above will be limited (see
Table 4-1).
WHO estimates that the daily average mercury intake by inhalation of
ambient air is at 0.04-0.2 µg Hg per day, based on an air concentration of
0.002-0.01 �g Hg/m 3
(Holmes et al., 2009).
Mercury in the form of thiomersal – an ethyl mercury compound – is in some
cases used as a preservative in vaccines. This use may also cause mercury
loads. It has been calculated that children subject to an ordinary children’s
vaccine programme with mercury preserved vaccine from birth and until the
age of 6 months will be exposed to more than 0.1 �g Hg per day per kg of
body weight (IPCS, 1980; Clarkson et al, 2003).
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