Lanthanum

Lanthanum (La) is a nonessential element. In its pure form, it is a rather soft, silvery-white metal, which tarnishes rapidly in the air. Its atomic weight is 138.9055 and its atomic number is 57. Rare earth elements including La are relatively abundant in the Earth's crust, but finding them where they can be economically mined and processed presents a challenge. China is presumed to be responsible for over 95% of the world's mine production. The chemistry of La primarily concerns its formation of the ionic +3 oxidation state. Lanthanum oxide improves the alkali resistance of glass: it is used in making special optical glasses, such as infrared-absorbing glass, as well as camera and telescope lenses, because of the high refractive index and the low dispersion of rare-earth glass. Small amounts of lanthanum added to steel improve its malleability. Microelement fertilizers with lanthanum as the main component have been used in Chinese plant production for about 30 years to improve yield and quality. In the general population, the mean dietary intake of La and lanthanides is estimated to be below 150 μg, which is less than 5% of the estimated acceptable daily intake. Lanthanum in drinking water samples is reported to be below 10 μg/L. Lanthanum carbonate as a drug was approved for human use by the US Food and Drug Administration in 2004 and by the European Union in 2006 to reduce serum phosphate levels in chronic kidney failure. For its administration to patients with end-stage renal failure, the lanthanum salt is given in the form of chewable tablets, at a maximal dose of 3000 mg per day. The absorption of La salts from the gut, as well as from the lungs, of humans is negligible or very small. Few side effects have been reported after oral intake of lanthanum carbonate as a drug. Gastrointestinal disturbances such as diarrhea, vomiting, and abdominal pain may occur. Myalgia, hypotension, and occasional cases of mental confusion have also been reported. Therapeutic administration of lanthanum salt will interact with the absorption of some other drugs, as the lanthanum cation can react with anionic forms of some compounds such as tetracyclines and quinolones.