This article is from the Amalgam-Related Illness FAQ, by Leif Hedegard.
According to WHO (WHO 1991) these are the general sources of mercury in the body (ug / day):
Yes, mercury vapour from dental amalgam alone is, on a group level, a bigger source than all the other sources together. Breast milk from fish-eating mothers can be quiet high in mercury.
There is some debate whether amalgam or fish is the biggest mercury-source in the general population even though the WHO-report clearly states amalgam as the biggest source. The WHO report based their data on intake alone.
Excretion and accumulation in non-amalgam bearers vs. amalgam-bearers, as shown below, also points strongly in the direction that amalgam is the single biggest mercury-source in non-occupationally exposed amalgam-bearers on a group level.
In individuals and in sub-populations consuming much fish and / or consumes a high proportion highly mercury-contaminated fish, the fish can be the biggest source of mercury.
The major part of absorbed mercury is excreted in urine and feces.
Over 90% of the mercury excreted via feces comes from dental amalgam (Barregard 1995, Bjorkman 1997, Edlund 1996, Osterblad 1995, Skare1994. This is based on comparison of non-occupationally exposed amalgam-bearers on the one hand, and non amalgam-bearers on the other hand. How much of this Hg that passes right through the gastro-intestinal canal is not clear, however it is usually assumed that 5-20% of inorganic mercury in the gastro-intestinal canal is absorbed.
Approximately 75% of the mercury excreted via urine comes from dental amalgam according to most reports (Begerow 1994, Berglund 1990, Molin 1990, Molin 1995, Schulte 1994, Zander 1990). However, Gebel (1996) reported 60%. These mercury values in urine are based on comparison of non-occupationally exposed amalgam-bearers on the one hand, and non amalgam-bearers on the other hand.
Conclusion is that dental amalgam is by far the biggest source to excreted mercury.
In deceased adult humans there is, on a group level, a correlation between the amount of Hg in brain and the number of amalgam-fillings (Nylander 1987, Weiner 1993). The presence of raised mercury levels, in it self, does not necessarily cause pathologic reactions - the levels will have to exceed a persons threshold level. The problem is that we do not know the lowest possible threshold level in brain / Central Nervous System (CNS), especially not in sensitive individuals. "There is very little information available on brain mercury levels in cases of mercury poisoning, and nothing that makes it possible to estimate a no-observed-effect level or a dose-response curve" ( WHO 1991 p20). But the levels in brain / Central Nervous System (CNS) from amalgam-fillings alone ARE, on a group level, BELOW the levels that occupationally exposed individuals, for example dentists, show without being diagnosed as suffering from mercury-poisoning (Nylander 1991).
In foetuses / children we have even less information about which mercury levels one could regard as safe. Therefore a report that show that mercury, from amalgam-fillings in the mother, passes over to the foetus in animals (Vimy 1990) has awoken some concern. Drasch (1994) has reported that mercury levels measured in deceased human foetuses (kidney cortex and liver) and deceased infants (kidney cortex and brain cortex) significantly correlate with the number of dental amalgam-fillings of the mother. Some levels in some children were above those of adults without amalgam, but the mercury levels in both foetuses and children did not, on a group level, exceed the levels of deceased amalgam-bearing adults have. However, some of the children in Drasch's report had mercury levels in their kidneys as high as those of amalgam-bearing adults or children.
Differences among individuals in how easy mercury is transported into the brain over the blood-brain barrier could possibly lead to different mercury-levels in brain in different individuals at a given whole-body dose of mercury. This could possibly explain some of the inter-individual differences in susceptibility to mercury; that is why some individuals get Central Nervous System symptoms at a given whole body dose while other do not. However, as far as I know it has never been investigated if deceased people with claimed / suspected amalgam-related illness has higher mercury levels in brain than control individuals in brain, although this would be interesting to know.
Also make sure to read these books: Poison in Your Teeth: Mercury Amalgam (Silver) Fillings...Hazardous to Your Health! and Mercury Detoxification by Tom McGuire