Cadmium is a soft, malleable metal usually found in zinc ore. Most of the cadmium encountered today is from nickel-cadmium batteries. Cadmium has eight stable isotopes and can bind to many different organic molecules. Cadmium has no known biological role in higher organisms and thus, is considered toxic.
When released into the atmosphere by smelting, mining, or other processes, cadmium compounds can travel long distances. It can then be deposited in the soil as it falls out of the air. Cadmium can move easily through soil layers and is taken up into the food chain via uptake by plants such as leafy vegetables, root crops, cereals, and grains. Because of the heavy use of chemical fertilizers in growing tobacco plants, cigarettes contain significant amounts of cadmium. Thus, blood cadmium concentrations are elevated in cigarette smokers and levels increase with the number of cigarettes smoked per day.
Cadmium tends to accumulate in the kidney and liver. The biological half-life of cadmium in the kidney is estimated to be between 6 to 38 years whereas the half-life in the liver is between 4-19 years.
Absorption:
Cadmium accumulation occurs over time and so the amount of cadmium in the body increases with age. If inhaled, 10-50% of cadmium is absorbed (depending on particle size). About 6% of orally ingested cadmium is absorbed, but up to 9% may be absorbed in those with iron deficiency. Because women are more likely to be iron deficient, women also tend to have higher amounts of cadmium.
Zinc and chromium compete with cadmium for absorption, so the presence of elevated zinc or chromium in the diet can decrease cadmium uptake. Absorption through the skin is low, with only about 0.5% of cadmium absorbed dermally.
