Short answers, pulled from the story.
Jöns Jacob Berzelius and Johan Gottlieb Gahn discovered selenium in 1817 while processing pyrite samples from the Falun Mine near Gripsholm, Sweden. Berzelius confirmed the discovery of the new element by 1818 and named it after the Greek goddess Selene to reflect its relationship to tellurium.
Willoughby Smith discovered the photoconductive properties of grey selenium in 1873, which allowed the element to function as a light-sensitive cell. This discovery led to the development of commercial selenium cells by Werner Siemens in the mid-1870s and enabled the transmission of sound via light beams in Alexander Graham Bell's photophone of 1879.
Selenium compounds confer a red color to glass and account for about 50% of global selenium consumption to cancel out green or yellow tints from iron impurities. Manufacturers add selenite and selenate salts to molten glass to produce clear or colored glass without the unwanted hues that naturally occur in silica-based materials.
The US Recommended Dietary Allowance for teenagers and adults is set at 55 micrograms per day. The human body contains between 13 and 20 milligrams of selenium, which functions as a cofactor for antioxidant enzymes such as glutathione peroxidase and thioredoxin reductase.
Selenium pollution caused catastrophic fish kills and reproductive failures in aquatic systems like Belews Lake in North Carolina and the Kesterson National Wildlife Refuge in California. Wastewater from a Duke Energy coal-fired power plant discharged selenium concentrations of 150 to 200 micrograms per liter into Belews Lake between 1974 and 1986, while agricultural irrigation drainage concentrated natural soluble selenium compounds in wetlands at Kesterson.
Grey selenium is the most stable and dense form with a chiral hexagonal crystal lattice consisting of helical polymeric chains where the selenium-selenium distance is 237.3 picometers. This form is a semiconductor showing appreciable photoconductivity and is insoluble in carbon disulfide, unlike other allotropes such as black or red selenium.