Cadmium

Cadmium was discovered in 1817 by the German chemist Friedrich Stromeyer, who traced a discoloration in a sample of zinc carbonate to a hidden new metal. He named it from cadmia, the old Latin and Greek name for calamine, the zinc ore in which he had found it. Cadmium is a soft, silvery-white metal, chemically close to zinc, and notably toxic; it was long used in bright yellow and red pigments and in rechargeable batteries and plating. Because of its toxicity many former uses in pigments, plating and plastics stabilisers have since been restricted, but cadmium remains important in nickel-cadmium rechargeable batteries and in some thin-film solar cells and specialised alloys.

Cadmium's toxicity produced one of the twentieth century's starkest environmental health disasters: in Japan's Jinzu River basin, decades of cadmium-laced mine wastewater contaminated rice paddies and drinking water, causing itai-itai disease, so named for the pained cries of sufferers whose bones softened and fractured; the disease, recognised from the 1910s but not officially linked to cadmium until the 1960s, became one of Japan's four major officially recognised pollution diseases. Cadmium yellow, meanwhile, became a favourite pigment of painters including Van Gogh and Monet for its intense, stable brightness, a striking contrast between the same element's artistic value and its industrial harm.

The word cadmia, and thus cadmium, descends from Cadmus, the hero of Greek legend who founded the city of Thebes. Cadmus, sent to find his sister Europa after her abduction by Zeus, instead slew a dragon and sowed its teeth, from which sprang armed men; he is also credited in myth with bringing the alphabet to Greece. His name became attached in antiquity to certain earths and ores of the Thebes region, calamine among them, and so passed, by a long thread, to the metal Stromeyer drew out of zinc ore. The connection is etymological rather than symbolic, but it lends this modern, toxic metal a surprising descent from one of the founding heroes of Greek myth. Cadmium yellow later became a treasured pigment of painters.

Cadmium's industrial retreat accelerated after the European Union's RoHS directive, adopted in 2003 and in force from July 2006, restricted the metal, along with lead and mercury, in most electronic and electrical equipment, part of a broader regulatory response to the same toxicity that caused itai-itai disease. Nickel-cadmium batteries, once the standard rechargeable technology in cordless tools and electronics, have been steadily displaced by nickel-metal-hydride and lithium-ion chemistries, partly for environmental reasons and partly because NiCd cells suffer a well-known memory effect that gradually reduces their usable capacity if repeatedly recharged before fully discharged.