CHAPTER 2-99: MERCURY

INTRODUCTION

Mercury (Hg) is a naturally occurring metal that is mined chiefly as HgS in cinnabar ore. It is converted to three primary forms, each with a distinct toxicology: elemental (metallic) mercury (Hg⁰), inorganic mercury salts (eg, mercuric chloride [HgCl₂]), and organic (alkyl and aryl) mercury (eg, methylmercury). Approximately one-half to one-third of commercial mercury use is in the manufacture of chlorine and caustic soda, one-half to one-third in electric equipment, and the remainder in various applications, such as dental amalgam, fluorescent lamps, switches, thermostats, and artisanal gold production. In the United States, mercury use in batteries and paints has been discontinued. Previous use in pharmaceuticals and biocides has declined sharply, although mercuric chloride is still used as a stool fixative, and some organomercury compounds (such as mercurochrome, phenylmercuric acetate, and thimerosal) are still used as topical antiseptics or preservatives. Some folk medicines contain inorganic mercury compounds, and some Latin American and Caribbean communities have used elemental mercury in religious or cultural rituals. Hazardous exposure has resulted from dermal use of imported skin lightening creams formulated with inorganic mercury salts. Aquatic organisms can convert inorganic mercury into methylmercury, with resulting bioaccumulation in large carnivorous fish such as swordfish. Mercury is released to the environment from the burning of coal and from fugitive emissions during the large-scale mining of gold. In an effort to curtail the use of elemental mercury in artisanal gold mining and other pathways of environmental mercury pollution, the European Union has enacted a ban on the export of most inorganic mercury effective 2011; a US ban on export of elemental mercury took effect in 2013.

MECHANISM OF TOXICITY

Mercury reacts with sulfhydryl (SH) groups, resulting in enzyme inhibition and pathologic alteration of cellular membranes.

1. Elemental mercury and methylmercury are particularly toxic to the CNS. Metallic mercury vapor is also a pulmonary irritant. Methylmercury is associated with neurodevelopmental disorders.

2. Inorganic mercuric salts are corrosive to the skin, eyes, and GI tract and are nephrotoxic.

3. Inorganic and organic mercury compounds may cause contact dermatitis.

TOXIC DOSE

The pattern and severity of toxicity are highly dependent on the form of mercury and the route of exposure, mostly because of different pharmacokinetic profiles. Chronic exposure to any form may result in toxicity (see Table II–37 for a summary of absorption and toxicity).

1. Elemental (metallic) mercury is a volatile liquid at room temperature.

   1. Hg⁰ vapor...