Critical observations on the neurotoxicity of silver.

Silver is a xenobiotic element with no recognized trace metal value in the human body. It is absorbed into the body through the lungs, gastrointestinal tract, mucus membranes of the urinogenital tract, and through the skin, mainly in the form of silver protein complexes. Although silver is metabolized throughout the soft tissues, available evidence from experimental animal studies and human clinical reports has failed to unequivocally establish that it enters tissues of the central nervous system or is a cause of neurotoxic damage. Argyria characterized by deposition of particles of silver sulfide or silver selenide is the principle contraindication for using silver in medical devices or occupationally. This presents discoloration of the skin but is not regarded as a health risk or manifestation of toxicity. No evidence is available to demonstrate the toxic risk of silver to the peripheral nervous system, although silver sulfide deposits have been identified in the region of cutaneous nerves. Transitory silver sulfide deposits seen in the tissues of the blood-brain and blood-CSF barriers are mostly lysosomally bound or deposited on basement membranes or collagen without toxic effect. Silver is mostly excreted from the body in the urine and feces. Further research is indicated to evaluate the role of metal binding proteins including metallothioneins as cytoprotectants for neurological tissue.