Health problems caused by mercury exposure depend on its metallic form, as well as the timing and dosage. The uptake of food-related organic mercury is six times higher than the uptake of mercury from amalgam restorations. The organic form of mercury in fish is absorbed more readily than inorganic mercury or mercury vapor from dental amalgam. Organic mercury easily crosses the blood-brain barrier. Elemental mercury vapor is absorbed by the lungs, and is transported through the blood to the brain and other tissues.
Elemental mercury is excreted mainly by the kidneys.
People with amalgam restorations have higher mercury levels in their body fluids than people without such restorations. The mercury levels are typically less than 5 micrograms per liter in urine, and 2.5 micrograms per liter in blood. Most individuals with amalgam restorations absorb less than 5 micrograms of mercury per day. The World Health Organization has recommended an upper limit of 1 microgram of inhaled mercury per cubic meter of inhaled air for children, pregnant women, and sick people. The daily recommended limit for mercury absorbed by the lungs is 20 micrograms.