Mercury Poisoning — How It Damages the Body

Mercury that enters the body goes everywhere, but accumulates especially in kidneys, brain, and fetus.

Why the nervous system

Methylmercury dissolves well in lipids. The brain has the highest lipid fraction of any organ. And methylmercury binds to amino acids like cysteine, forming L-cysteine-methylmercury that disguises as an amino acid and crosses the blood-brain barrier through transporters.

Inside the brain, methylmercury binds to sulfur-containing (SH) proteins and enzymes. It disrupts microtubule assembly, depletes glutathione, and disturbs calcium homeostasis. Neurons die.

Chronic methylmercury symptoms

• Paresthesia: tingling around fingertips, toes, lips. Most common early sign

• Ataxia: can't walk straight, fine motor tasks like scissoring become difficult

• Tunnel vision: peripheral vision narrows, eventually can't drive

• Hearing loss: high frequencies fade first

• Dysarthria: slurred speech

• Cognitive decline: weakened memory, concentration, judgment

Symptoms don't appear at once — they progress slowly over 6 months to years. So people dismiss them as "just tired" until major damage is done.

Acute vs chronic

Acute (high-dose short exposure): industrial accidents inhaling mercury vapor. Pneumonia, respiratory failure, kidney damage within days. Can be fatal.

Chronic (low-dose long exposure): fish consumption, dental workers, miners, environmental exposure. Neurological symptoms appear gradually.

The latter is what matters for frequent tuna eaters. Eating one serving of swordfish sashimi daily for a year pushes hair mercury above safe thresholds.

Inorganic mercury target: kidneys

Inorganic mercury (Hg²⁺) hits kidneys more than nerves. Accumulates in proximal tubule cells, causes proteinuria and renal failure.

Historically there were suicide attempts using mercuric chloride (sublimate, HgCl₂). Renal failure and death within 24 hours.

Fetus — most vulnerable

Methylmercury crosses the placenta freely. The developing fetal brain takes much greater damage at the same concentration than an adult brain.

Mercury from a pregnant woman's tuna concentrates 1.5~2× in fetal blood. That's why "no large fish during pregnancy" isn't just a soft suggestion — it has strong medical evidence.