Mercury

Mercury (Hg) is a non-essential metal that has the unique property of being a liquid with a measurable vapour pressure at ambient temperature. Mercury exists in elemental, inorganic [Hg(I), Hg(II)) and organic (e.g. methylated forms). Absorption of elemental and inorganic mercury is negligible when ingested and relatively harmless. However, greater than 80% of elemental mercury is absorbed when inhaled, which may give rise to pneumonitis and pulmonary oedema. In contrast > 90% of organic mercury is absorbed from the intestine and phenyl mercury is absorbed through the skin. Toxicity from organic mercury usually manifests as CNS disturbances (e.g. ataxia, muscle weakness, tremor). Organic mercury is found in fish and bioaccumulates in the food chain, therefore large predatory fish (e.g. tuna, swordfish) may have high concentrations of organic mercury in their tissues.

If exposure to elemental or inorganic mercury is suspected urine is the preferred sample. Conversely if exposure to organic mercury is suspected, a blood sample is preferred, if there is doubt a blood sample should be sent. The preservative, thiomersal should not be used.