"XTRA". XTRA. Archived from the original on 19 February 2013. Retrieved 5 July 2012.
nytimes.com
Bradsher, Keith (8 March 2011). "Taking a Risk for Rare Earths". The New York Times. Archived from the original on 30 November 2016. Retrieved 24 February 2017.
Bradsher, Keith (30 June 2011). "The Fear of a Toxic Rerun". The New York Times. Archived from the original on 15 August 2018. Retrieved 24 February 2017.
Bradsher, Keith (8 March 2011). "Taking a Risk for Rare Earths". The New York Times. Archived from the original on 30 November 2016. Retrieved 24 February 2017.
Bradsher, Keith (30 June 2011). "The Fear of a Toxic Rerun". The New York Times. Archived from the original on 15 August 2018. Retrieved 24 February 2017.