Cadmium
Friedrich Stromeyer isolated a new element in 1817 while examining zinc carbonate samples sold to pharmacies in Germany. He noticed that impure calamine changed color when heated, unlike pure calamine which remained stable. Karl Samuel Leberecht Hermann investigated the same discoloration in zinc oxide at the same time and found an impurity he first suspected was arsenic due to a yellow precipitate with hydrogen sulfide. The metal took its name from cadmia, the Latin word for calamine, which itself derived from the Greek mythological character Cadmus. For one hundred years following this discovery, Germany stood as the only important producer of the metal. Early pharmaceutical records show that cadmium iodide appeared in the British Pharmaceutical Codex of 1907 as a treatment for enlarged joints and chilblains.
Cadmium presents as a soft, malleable, ductile, silvery-white divalent metal that resists corrosion better than most other metals. It forms complex compounds similar to zinc but possesses a lower melting point than transition metals in groups three through eleven. Unlike many elements, cadmium does not have partly filled d or f electron shells in its elemental or common oxidation states. In air, it burns to form brown amorphous cadmium oxide (CdO) while the crystalline form appears dark red and changes color upon heating. Hydrochloric acid dissolves the metal to create cadmium chloride, sulfuric acid creates cadmium sulfate, and nitric acid produces cadmium nitrate. Powdered cadmium may burn and release toxic fumes even though bulk metal remains insoluble in water and non-flammable.
The industrial scale production of cadmium began in the 1930s and 1940s with major applications focused on coating iron and steel to prevent corrosion. By 1944, sixty-two percent of cadmium used in the United States went toward plating, rising slightly to fifty-nine percent by 1956. The stabilizing effect of carboxylates like cadmium laurate on PVC led to increased usage during the 1970s and 1980s. Environmental regulations in the 1980s and 1990s caused demand for pigments and coatings to decline sharply. By 2006, only seven percent of total consumption went to plating and ten percent to pigments. This drop was compensated by a growing demand for nickel-cadmium batteries which accounted for eighty-one percent of US consumption that same year. In 2009, eighty-six percent of all cadmium worldwide ended up inside batteries rather than other products.
Cadmium makes up about 0.1 parts per million of Earth's crust and ranks as the 65th most abundant element globally. No significant deposits of pure cadmium-containing ores exist because greenockite is nearly always associated with sphalerite zinc ore. Mining operations in the Vilyuy River basin in Siberia yield metallic cadmium alongside zinc production. Coal contains significant amounts of cadmium which ends up mostly in coal fly ash after combustion. Rocks mined for phosphate fertilizers contain varying amounts resulting in concentrations as high as 300 milligrams per kilogram in the fertilizer itself. In 2002, the Chinese ministry of agriculture measured that twenty-eight percent of sampled rice had excess lead and ten percent exceeded legal limits for cadmium. Consumer Reports tested twenty-eight brands of dark chocolate sold in the United States in 2022 and found cadmium in every single sample.
The Jinzū River area in Japan became contaminated with cadmium during mining operations decades before World War II. Cadmium accumulated in rice crops along the riverbanks downstream of the mines where local agricultural communities consumed the grain. Victims developed itai-itai disease and renal abnormalities including proteinuria and glucosuria. These victims were almost exclusively post-menopausal women suffering from low iron levels and poor mineral stores. Exposure to cadmium leads to raised blood cell levels for several months while elimination occurs mainly through urine over a biological half-life of twenty to forty years. Inhalation of fine dust or fumes can result initially in metal fume fever but may progress to chemical pneumonitis, pulmonary edema, necrosis, and death. Tobacco plants absorb heavy metals like cadmium from soil into their leaves making smoking the most important source of exposure for the general population.
In May 2006, a sale of seats from Arsenal F.C.'s old stadium Highbury in London was cancelled after discovering trace amounts of cadmium. Reports of high cadmium levels in children's jewelry led to a US Consumer Product Safety Commission investigation in 2010. The U.S. CPSC issued specific recall notices for cadmium content in jewelry sold by Claire's and Wal-Mart stores. In June 2010, McDonald's voluntarily recalled more than twelve million promotional Shrek Forever After 3D Collectible Drinking Glasses due to paint pigments containing cadmium. The European Union banned cadmium under the Restriction of Hazardous Substances directive which regulates hazardous substances in electrical equipment. The International Agency for Research on Cancer classified cadmium compounds as carcinogenic to humans while OSHA set the permissible exposure limit at 0.005 parts per million time-weighted average.
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Common questions
Who discovered cadmium and when was it isolated?
Friedrich Stromeyer isolated a new element in 1817 while examining zinc carbonate samples sold to pharmacies in Germany. Karl Samuel Leberecht Hermann investigated the same discoloration in zinc oxide at the same time and found an impurity he first suspected was arsenic due to a yellow precipitate with hydrogen sulfide.
What is the chemical composition of cadmium oxide formed during combustion?
In air, cadmium burns to form brown amorphous cadmium oxide (CdO) while the crystalline form appears dark red and changes color upon heating. Hydrochloric acid dissolves the metal to create cadmium chloride, sulfuric acid creates cadmium sulfate, and nitric acid produces cadmium nitrate.
How much cadmium was used for batteries in the United States by 2006?
By 2006, only seven percent of total consumption went to plating and ten percent to pigments. This drop was compensated by a growing demand for nickel-cadmium batteries which accounted for eighty-one percent of US consumption that same year.
Where did cadmium contamination cause itai-itai disease in Japan?
The Jinzū River area in Japan became contaminated with cadmium during mining operations decades before World War II. Cadmium accumulated in rice crops along the riverbanks downstream of the mines where local agricultural communities consumed the grain.
When did McDonald's recall Shrek glasses due to cadmium content?
In June 2010, McDonald's voluntarily recalled more than twelve million promotional Shrek Forever After 3D Collectible Drinking Glasses due to paint pigments containing cadmium. Reports of high cadmium levels in children's jewelry led to a US Consumer Product Safety Commission investigation in 2010.