Calcium oxalate

Calcium oxalate is a chemical compound that forms needle-shaped crystals. Large quantities are found in the poisonous plant dumb cane. It is also found in rhubarb leaves, various species of Oxalis, and agaves, and (in lower amounts) in spinach. Calcium oxalate crystals in the urine are the most common constituent of human kidney stones, and calcium oxalate crystal formation is also one of the toxic effects of ethylene glycol poisoning.

Even a small dose of calcium oxalate is enough to cause intense sensations of burning in the mouth and throat, swelling, and choking. In larger doses, however, calcium oxalate causes severe digestive upset, breathing difficulties and - if enough is consumed - convulsions, coma and death. Recovery from severe oxalate poisoning is possible, but permanent liver and kidney damage may have occurred.

Nonsoluble calcium oxalate crystals are found in plant stems, roots, and leaves. The stalk of the Dieffenbachia produces the most severe reactions. These needle-like crystals produce pain and edema when they contact lips, tongue, oral mucosa, conjunctiva, or skin. Oedema primarily is due to direct trauma from the needle-like crystals and, to a lesser extent, by other plant toxins (e.g. bradykinins, enzymes).

Calcium oxalate also forms a major component of beerstone, a brownish precipitate that tends to accumulate within vats, barrels and other containers used in the brewing of beer. Beerstone is composed of calcium and magnesium salts and various organic compounds left over from the brewing process; it promotes the growth of unwanted microorganisms that can adversely affect or even ruin the flavor of a batch of beer.