https://kottke.org/17/11/the-periodic-table-of-endangered-elements
https://www.weforum.org/agenda/2017/11/the-periodic-table-of-endangered-elements/
https://www.acs.org/content/acs/en/greenchemistry/research-innovation/endangered-elements.html
https://www.compoundchem.com/2015/08/19/endangered-elements/
https://www.chemie.de/infografiken/249/the-periodic-table-of-endangered-elements.html