Children living near Bitterfeld and Hettstedt in East Germany - centres of coal mining, chemical production and metal smelting - were found to have various high levels of mercury in their blood and urine. Tests were unable to correlate the different levels with levels of pollution. The only correlation the researchers could find was with the number of amalgam fillings the children had. To double check whether environmental pollution was the cause the researchers measured the blood and urine levels of children without any fillings in differently polluted areas but there were no significant differences.

Mercury from amalgam fillings is released by direct vaporisation from metallic mercury contained in the amalgam. The amount of gas is increased by grinding the teeth or chewing. Correlations between the number of amalgam fillings and mercury levels in blood and urine has now been reported in several studies.