to 0.1 mg/m3 over an eight-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set the recommended exposure limit (REL) at 0.1 mg/m3 over an eight-hour workday. In concentrations of 25 mg/m3, tellurium is immediately dangerous to life and health. See also The 1862 telluric helix of Alexandre-Émile Béguyer de Chancourtois. References Cited sources External links USGS Mineral Information on Selenium and Tellurium Tellurium at The Periodic Table of Videos (University of Nottingham) CDC – NIOSH Pocket Guide to Chemical Hazards – Tellurium Chemical elements Chalcogens Metalloids Trigonal minerals Minerals in space group 152 or 154 Native element minerals Chemical elements with trigonal structure Crystals in space group 152 or 154