Bismuth: The Element of Surprise

Bismuth is a metallic element with surprisingly low toxicity. The Safe Drinking Water Act Amendment of 1996 requires that all new and repaired pipes for drinking water be lead-free; accordingly, bismuth has been an important low-toxicity replacement for lead in solders used in pipes that carry safe drinking water. The image to the right is crystalline bismuth; such crystals are “grown” in a lab and only rarely take on this geometric appearance in nature. The many iridescent colors of crystalline bismuth are due to an extremely thin layer of bismuth oxide that forms on the surface of this metal. Elemental bismuth is one of only four substances in which the liquid is more dense than its solid (water is the best-known example; it is the reason that ice is able to float in liquid water).

When bismuth is combined in specific conditions with thiols (an extensive group of sulfur-containing compounds), bismuth-thiols are synthesized, typically taking the form of bright yellow powders. Bismuth-thiols have important applications as anti-infectives, medical device coatings, and industrial anti-biofouling agents. Another well-known bismuth salt is bismuth subsalicylate, the active ingredient in Pepto-Bismol™ and Kaopectate®.