Cyanide's deadly hold over gold

The Romanian cyanide spill devastated the River Tisza

By BBC science correspondent Richard Black

Cyanide is a highly toxic chemical - less than one gram can be fatal to humans - and river spills can do enormous damage to wildlife and ecosystems.

The principal application of sodium cyanide is in mining precious metals, especially gold, where it is used to separate the metal from its ore.

But there has been concern for many years over leaks and spills.

Thousands of fish died in three countries

In January 2000, waste containing sodium cyanide flowed into the River Tisza, a tributary of the Danube, following a dam burst at a goldmine in Romania.

The accident killed around 80% of fish in the Tisza, and devastated local populations of birds and other animals.

It sparked a bitter political confrontation over responsibility and compensation, between the multinational company operating the mine and the governments of Romania, Hungary and Serbia.

According to the environmental organisation the Mineral Policy Centre, which monitors the mining industry, cyanide spills are a risk in almost every gold mining area.

As scientists have yet to come up with an alternative process which avoids cyanide and yet is both technically and economically feasible, it is a risk which seems set to remain.