Cadmium is a toxic heavy metal with no known biological role in humans. It is found naturally in the environment and is released in higher concentrations through industrial processes including mining, smelting, battery manufacturing, and phosphate fertiliser production. Humans are primarily exposed through cigarette smoking (tobacco plants accumulate cadmium from soil), food (particularly rice, vegetables, and organ meats from cadmium-contaminated soils), and occupational settings.

Cadmium accumulates in the kidneys, liver, and bones over decades. Because its biological half-life is 10–30 years, even modest chronic exposure leads to gradual body burden accumulation. At elevated concentrations, cadmium causes kidney tubular damage (reducing the ability to reabsorb proteins and phosphate), bone demineralisation (itai-itai disease, first identified in Japan), and is classified as a Group 1 carcinogen, associated with lung, kidney, and prostate cancer.