Elemental mercury is found in liquid form, which easily vaporizes at room temperature and is well absorbed through inhalation. Its lipid (fat)-soluble property allows for easy passage through the alveoli into the bloodstream and red blood cells. Once inhaled, elemental mercury is mostly converted to an inorganic divalent or mercuric form by catalase in the red blood cells. This inorganic form has similar properties to organic mercury. Small amounts of non-oxidized elemental mercury continue to persist and account for CNS toxicity. Elemental mercury, as a vapor, which escapes from fillings, penetrates the blood-brain-barrier and enters the CNS, where it's ionized and trapped, attributing to its significant toxic effects. It is not well absorbed by the GI tract and, when ingested, is only mildly toxic. Inorganic mercury is highly toxic and corrosive and is the most destructive form, but its destruction is limited to where it's located. It doesn't have the ability to move through tissues like other forms. It gains access orally or dermally and is absorbed at a rate of 10% of that ingested. It has a nonuniform mode of distribution, secondary to poor fat solubility, and accumulates mostly in the kidney, causing renal damage.

Although poor lipid solubility characteristics limit CNS penetration, slow elimination and chronic exposure allow for significant CNS accumulation of mercuric ions and subsequent toxicity. Chronic dermal exposure to inorganic mercury also may lead to toxicity. Excretion of inorganic mercury, as with organic mercury, is mostly through feces. Renal excretion of mercury is considered insufficient and attributes to its chronic exposure and accumulation within the brain, causing CNS effects. Organic mercury can be found in 3 forms, aryl and short and long chain alkyl compounds. This is 100 times more toxic than the ionic or vapor forms. Bacteria in the mouth, stomach and intestines, or in the blood, through a process called methylation, converts mercury vapor and ionic mercury into deadly methylmercury.