Cadmium Toxicity

Cadmium is a soft, silvery-white metal grouped with zinc and mercury on the periodic table, and appears to be a potent neurotoxin to the developing nervous system of the fetus and newborn baby. Like mercury, it is very reactive in the presence of vital sulfhydral-containing enzymes and proteins in the body.

Cadmium is found naturally in the environment, though never in its elemental state, usually in association with zinc. Some of the most common sources of cadmium in our environment are as a byproduct of zinc smelting and burning of fossil fuels. It is also associated with mining operations, battery production, incineration of municipal waste, and with sludge-based and phosphate fertilizers. Approximately thirty-six hundred tons were used in 1985 alone for metal-plating processes, in paint pigments, plastic stabilizers, and in Ni-Cad (nickel cadmium) batteries. As a component of many disposable consumer goods, cadmium eventually ends up in landfills, much of which is burned, releasing this toxic substance into the atmosphere.

The primary source of exposure for most individuals who do not work in a cadmium-based industry is from food sources. The average daily uptake has risen to approximately 10-30 ug. Many leafy plants absorb cadmium from the soil, especially when sludge-type fertilizers are used. Organ meats, such as kidney and shellfish also contain significant amounts of cadmium.

Inhalation of cadmium released from factories, landfill incineration, and cigarettes is the second major source of exposure. Second-hand smoke is dangerous as well, and presents a particular danger to newborns and small children. Absorption of cadmium from the lungs varies from 30 percent to as high as 90 percent.

Once cadmium enters the body, only 1-5 percent is absorbed from the gastrointestinal tract in adults, but in newborns absorption is much higher, sometimes as much as 55 percent. Once absorbed, the metal quickly binds to the membranes of red blood cells, and to albumin, where it is quickly removed by the liver and especially the kidney. Not surprisingly then, the kidneys are the principal sites of cadmium toxicity. As with mercury toxicity, metalloth-ioneins are considered to be the principal method of detoxification within the liver, kidneys, and cells.

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