furiosus A wtp system is known to selectively transport tungsten in archaea: WtpA is tungsten-binding protein of ABC family of transporters WptB is a permease WtpC is ATPase Health factors Because tungsten is a rare metal and its compounds are generally inert, the effects of tungsten on the environment are limited. The abundance of tungsten in the Earth's crust is thought to be about 1.5 parts per million. It is one of the rarer elements. It was at first believed to be relatively inert and an only slightly toxic metal, but beginning in the year 2000, the risk presented by tungsten alloys, its dusts and particulates to induce cancer and several other adverse effects in animals as well as humans has been highlighted from in vitro and in vivo experiments. The median lethal dose LD50 depends strongly on the animal and the method of administration and varies between 59 mg/kg (intravenous, rabbits) and 5000 mg/kg (tungsten metal powder, intraperitoneal, rats). People can be exposed to tungsten in the workplace by breathing it in, swallowing it, skin contact, and eye contact. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday and a short term limit of 10 mg/m3. See also Field emission gun Tungsten oxide List of chemical elements name etymologies List of chemical elements naming controversies References External links Properties, Photos, History, MSDS CDC – NIOSH Pocket Guide to Chemical Hazards Tungsten at The Periodic Table of Videos (University of Nottingham) Picture in the collection from Heinrich Pniok Elementymology & Elements Multidict by Peter van der Krogt – Tungsten International Tungsten Industry Association Chemical elements Transition metals Refractory metals Chemical elements with body-centered cubic structure Native element minerals