How Does Mercury Leave the Body — Excretion Pathways and Limits

Mercury excretion uses four main routes. Each pathway handles different mercury forms differently.

1. Stool (main route for methylmercury)

In the liver, methylmercury binds glutathione (GSH) and exits via bile → intestine → stool.

But there's a catch. Some methylmercury in the gut is reabsorbed (enterohepatic circulation). That's why excretion is slow.

Solution: dietary fiber. Fiber binds the methylmercury-bile complex in the gut and blocks reabsorption. Vegetables and seaweed are the "slow but real" method.

2. Urine (main route for inorganic mercury)

Inorganic mercury (Hg²⁺) is filtered by kidneys into urine. Part of methylmercury is also converted to inorganic mercury then excreted in urine.

That's why exposure tests measure urine mercury (mostly inorganic exposure), blood mercury (recent methylmercury), and hair mercury (long-term methylmercury) separately.

3. Hair

Methylmercury in blood travels to hair follicles and binds SH groups in hair proteins. It stays as a record while the hair grows.

1cm of growth = 1 month of exposure record. Sectional analysis of hair tells "when the exposure happened." This is how Minamata patients' hair was analyzed.

Blood:hair mercury ratio is roughly 1:250. So 5μg/L in blood → 1.25μg/g in hair.

4. Breast milk

Methylmercury in nursing mothers also exits via breast milk. Concentration is about 5~10% of blood. Sounds small but it's chronic exposure for the infant.

That's why "avoid large fish" extends through pregnancy and nursing.

Half-lives

• Methylmercury (CH₃Hg⁺): 70~80 days

• Inorganic mercury (Hg²⁺): 30~60 days in kidney, longer elsewhere

• Metallic mercury vapor (Hg⁰, after oxidation): ~60 days

• Methylmercury accumulated in brain: years to lifetime (barely leaves the brain)

Brain accumulation barely leaving is the real problem. Neurological symptoms recover slowly or permanently even after exposure ends.

Chelation therapy

For severe poisoning, doctors prescribe chelators like DMPS or DMSA. They bind mercury and accelerate urinary excretion.

Warning: using OTC detox products without medical supervision can pull mercury from tissues into blood, paradoxically increasing nervous system exposure. Self-administered detox is dangerous.

Selenium reportedly binds methylmercury into selenomethylmercury, reducing toxicity. Selenium-rich foods (Brazil nuts, sardines, sunflower seeds) show partial protection. But selenium overdose is also toxic — don't blast supplements.

Real "detox"

• Stop more from coming in (cut large fish)

• Fiber to block enterohepatic recycling

• Time — half disappears in 2.5 months, quarter in 6 months naturally

• Severe cases: chelation under medical supervision

"Mercury detox teas/drinks" are ineffective or marginal. Better: don't let it in.