Mercury

Mercury is a naturally occurring metal that’s harmful to human health in all its forms: elemental, inorganic, and organic. The danger it poses depends on how it enters the body:

• Elemental Mercury (metallic form): This is the silvery liquid, also called “quicksilver,” found in some older thermometers, fluorescent light bulbs, and industrial equipment. It can vaporize at room temperature, and inhaling these vapors is highly toxic, especially in occupational settings like artisanal gold mining or manufacturing.
• Inorganic Mercury Salts: These occur in compounds like mercuric chloride and are found in certain skin-lightening creams, traditional medicines, or industrial processes like electroplating. They are absorbed through ingestion or skin contact and can severely damage the kidneys and gastrointestinal tract.
• Organic Mercury (e.g., methylmercury): The most common exposure for the general public, especially through eating predatory fish like shark, swordfish, or tuna. Methylmercury is a fat-soluble form that crosses into the brain and placenta, making it particularly dangerous during pregnancy.

Mercury exposure interferes with enzymes and cellular energy production, leading to damage in the brain, nervous system, and kidneys. Inhaled mercury vapor targets the lungs and brain, while swallowed inorganic mercury mainly harms the digestive system and kidneys. Methylmercury is especially concerning because it crosses into the brain and placenta, making pregnant women and developing fetuses particularly vulnerable.

Symptoms depend on the form and level of exposure.

• Acute elemental mercury inhalation can cause life-threatening lung inflammation (pneumonitis), chest pain, and breathing difficulty.
• Chronic inhalation leads to tremors, insomnia, mood changes (known historically as “Mad Hatter syndrome” or erethism), and cognitive decline.
• Inorganic mercury damages the kidneys, often causing nephrotic syndrome or tubular dysfunction.
• Methylmercury concentrates in brain tissue, especially in developing fetuses, where it causes irreversible neurodevelopmental damage—this is why pregnant women are advised to avoid high-mercury fish.

Treatment starts with removing the source of exposure. For elemental and inorganic forms, chelation therapy—a treatment that helps the body eliminate mercury—is recommended when mercury levels are high and symptoms are present. Chelation doesn’t work for organic mercury once it has entered the brain, so prevention is key.

Despite public concerns, dental amalgam fillings release very small amounts of mercury—far below harmful levels—and are not considered a health risk by health authorities. In contrast, high-mercury fish like shark, swordfish, and king mackerel should be avoided during pregnancy due to the risk of brain damage in the fetus.