General pathology · Environmental pathology
Heavy metals: lead, mercury, arsenic and cadmium !
- Topic
Lead, mercury, arsenic and cadmium bind proteins and enzymes; each one damages its own favourite organs: blood, brain, nerves, kidney or skin.
Updated 2026-11-01
What it is
Heavy metals stick to sulfhydryl groups of proteins and displace essential ions, which blocks enzymes and injures cells. Exposure comes from work, mining, old paint, contaminated water and food, and tobacco. Children and fetuses are the most vulnerable because their brains are still developing.
Key facts
- Lead is stored in bone for years and released slowly; in children it also lowers IQ permanently.
- Colombia is one of the countries with the highest mercury release from artisanal gold mining.
- Arsenic in groundwater is a problem in several Latin American regions as well as in South Asia.
- Chelating agents such as succimer and dimercaprol bind metals so they can be excreted.
Step by step
- Lead competes with zinc and iron and binds sulfhydryl groups of enzymes.
- It blocks ALA dehydratase and ferrochelatase: heme cannot be completed.
- ALA rises (a neurotoxin) and zinc protoporphyrin builds up in the red cell.
- Iron accumulates in mitochondria: ringed sideroblasts and a microcytic anaemia.
- Lead also blocks the enzyme that degrades ribosomal RNA: basophilic stippling of red cells.
The four metals to know
| Metal | Main sources | Target organs and lesions | Clues |
|---|---|---|---|
| Lead | Old paint, batteries, smelting, contaminated soil and water, glazed pottery | Microcytic anaemia, brain injury in children, motor neuropathy (wrist drop), kidney, colic | Basophilic stippling, ringed sideroblasts, lead lines in gums and bone metaphyses |
| Mercury | Fish with methylmercury, artisanal gold mining, vapour, handling of dental amalgam | Brain (fetal brain especially), tremor, kidney (proximal tubule), gums | Methylmercury crosses the placenta; Minamata disease |
| Arsenic | Contaminated groundwater, pesticides, smelting | Skin (hyperpigmentation, keratoses, carcinoma), neuropathy, lung, bladder and liver cancer | Mees lines on nails, palm and sole keratoses |
| Cadmium | Batteries, smelting, tobacco smoke, contaminated rice | Proximal tubule injury, bone loss (osteomalacia), emphysema when inhaled | Itai-itai disease in Japan |
Test yourself
Think of the answer, then tap the question to see it.
Which two heme enzymes does lead inhibit?
ALA dehydratase and ferrochelatase, which causes a microcytic anaemia with ringed sideroblasts and high zinc protoporphyrin.
What is basophilic stippling and in which poisoning is it classic?
Fine blue dots of undegraded ribosomal RNA in red cells; classic in lead poisoning.
Which form of mercury most harms the fetal brain and how does it reach people?
Methylmercury, which builds up in predatory fish and crosses the placenta.
Which skin signs suggest chronic arsenic exposure?
Patchy hyperpigmentation, keratoses of the palms and soles, Mees lines on the nails and later squamous or basal cell carcinoma.
Related
- Chemical (toxic) cell injury: direct and after metabolism
- Chemical carcinogens: initiation, promotion and the table to know
- Air pollution and occupational exposures
Related conditions
- Lead poisoning
- Mercury poisoning
- Arsenic poisoning
- Cadmium poisoning
- Sideroblastic anaemia
- Peripheral neuropathy (diabetic and other)
- Fanconi syndrome
- Gout
- Chronic kidney disease
- Osteoporosis
- Cutaneous squamous cell carcinoma
Elsewhere in DurgiPedia
In Pharmacology
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Lead poisoning: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Lead poisoning (World Health Organization, 2026); Mercury (World Health Organization, 2026); Arsenic (World Health Organization, 2026).
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Representative model, for educational purposes only.