Mercury: Beautiful but deadly
21 February 2014 Last updated at 10:12 GMT
Mercury is the bad-boy of the periodic table. Often called "quicksilver", it is both mesmerising and toxic, as Professor Andrea Sella of University College London vividly explains.
Justin Rowlatt speaks to Tim Kasten of the United Nations' Environment Programme, who is one of the architects of a new international treaty that aims to ban the metal from industrial uses by 2020.
As we discover, that ban will affect everything from coal-fired power stations to small-scale gold miners in developing countries.
We visit a fluorescent bulb recycling plant outside Norwich and speak to gold miners in Ghana about how the ban might affect them.
But it is all in a good cause, as Justin discovers when he visits one of the finest fishmongers in London.