Cadmium (BioDeep_00000004685)

描述信息

Cadmium (group IIB of the periodic table of elements) is a heavy metal. It is not a naturally occurring metal in biological systems. Cadmium poses severe risks to human health. Physiologically, it exists as an ion in the body. Up to this day, it has not been shown that cadmium has any physiological function within the human body. Interest has therefore risen in its biohazardous potential. As first described by Friedrich Stromeyer (Gottingen, Germany) in 1817, cadmium intoxication can lead to kidney, bone, and pulmonary damage. Cadmium is widely used in industrial processes, e.g as an anticorrosive agent, as a stabilizer in PVC products, as a colour pigment, a neutron absorber in nuclear power plants, and in the fabrication of nickel cadmium batteries. Phosphate fertilizers also show a big cadmium load. Although some cadmium containing products can be recycled, a large share of the general cadmium pollution is caused by dumping and incinerating cadmium polluted waste. In Scandinavia for example, cadmium concentration in agricultural soil increases by 0.2 percent per year. Total global emission of cadmium amounts to 7000 t/year. The maximum permissible value for workers according to German law is 15 ug/l. For comparison: Non-smokers show an average cadmium blood concentration of 0.5 ug/l. Basically there are three possible ways of cadmium resorption: Gastrointestinal, pulmonary and dermal. The uptake through the human gastrointestinal is approximately 5 percent of an ingested amount of cadmium, depending on the exact dose and nutritional composition. The major source of inhalative cadmium intoxication is cigarette smoke. The human lung resorbes 40 to 60 percent of the cadmium in tobacco smoke. Little research has been done on dermal absorption of cadmium. Two mechanisms facilitate cadmium absorption by the skin: binding of a free cadmium ion to sulfhydryl radicals of cysteine in epidermal keratins, or an induction and complexing with metallothionein. Once taken up by the blood, the majority of cadmium is transported bound to proteins, such as Albumin and Metallothionein. The first organ reached after cadmium uptake into the GI-blood is the liver. Here cadmium induces the production of Metallothionein. After consecutive hepatocyte necrosis and apoptosis, Cd-Metallothionein complexes are washed into sinusoidal blood. From here, parts of the absorbed cadmium enter the entero-hepatical cycle via secretion into the biliary tract in form of Cadmium-glutathione conjugates. Enzymatically degraded to cadmium-cysteine complexes in the biliary tree, cadmium reenters the small intestines. The main organ for long-term cadmium accumulation is the kidney. Here the half life period for cadmium is approximately 10 years. A life long intake can therefore lead to a cadmium accumulation in the kidney, consequently resulting in tubulus cell necrosis. The blood concentration of cadmium serves as a reliable indicator for a recent exposition, while the urinary concentration reflects past exposure, body burden and renal accumulation. Excretion of Cadmium takes place via faeces and urine. (PMID: 16961932).
Cadmium, also known as cadmium, ion (cd2+) or cadmium ion, is a member of the class of compounds known as homogeneous transition metal compounds. Homogeneous transition metal compounds are inorganic compounds containing only metal atoms,with the largest atom being a transition metal atom. Cadmium can be found in a number of food items such as capers, horseradish, malabar spinach, and wax apple, which makes cadmium a potential biomarker for the consumption of these food products. Cadmium can be found primarily in blood, cerebrospinal fluid (CSF), saliva, and urine. Moreover, cadmium is found to be associated with alzheimers disease, macular degeneration, multiple sclerosis, and parkinsons disease. Cadmium is formally rated as a carcinogenic (IARC 1) potentially toxic compound. Cadmium is a chemical element with symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11. Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in Earths crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate . Acute inhalation of cadmium fumes results in metal fume fever, which is characterized by chills, fever, headache, weakness, dryness of the nose and throat, chest pain, and coughing. Ingestion of cadmium causes vomiting and diarrhea (L6) (T3DB).

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