Used as a calcium antagonist in biology research; Used in optical glass; [ChemIDplus] Natural isotopes are stable La-139 (99.9%) and radioactive La-138 (0.09%); Derived from the minerals monazite, bastnaesite, and cerite; [Merck Index] Used in carbon lighting, optical glasses, metal alloys, lighter flints, electronic vacuum tubes, electron microscopes, hydrogen sponge alloys, petroleum cracking catalysts, gas lantern mantles, dating of rocks and ores, medications (phosphate binder), biological tracers, and scintillators; [Wikipedia] Used to make carbon lighting, alkali-resistant glass, optical glass, and nodular caste iron; [Reference #1] Used in special optical glasses (infra-red-absorbing glass, camera and telescope lenses) and in small amounts to improve malleability of steel; Also used as catalysts (cracking in petroleum refining and automotive catalytic converters), in nickel-metal-hydride rechargeable batteries, and in water treatment; Lanthanum carbonate is used as a drug to reduce serum phosphate levels in patients with kidney failure; [Nordberg, p. 903]
Low to moderate acute toxicity rating; [Reference #1] A printer and a movie projectionist exposed to rare earth metals in dusts of cored carbon arc lamps retained lanthanum in their lungs. Side effects (not dose dependent) of the drug lanthanum carbonate include diarrhea, vomiting, and abdominal pain. No liver toxicity has been reported. [Nordberg, p. 906-7] See "RARE EARTH METALS" and linked occupational diseases.