The exact composition of the sheet can be adjusted to the desired parameters. More specifically, the researchers have calibrated the sheet so that it changes colour when limits established by the Environmental Protection Agency (EPA) of the United States are exceeded: 2 ppb (parts per billion) of divalent mercury Hg(II), one of the most reactive, in water destined for human consumption.
Having also developed a method for other elements like iron or cyanide, the researchers believe that the water drunk in Spain "is of excellent quality due to highly efficient controls." Therefore, the technique could be used there for detecting mercury in certain spills and for studying its presence in fish.
A global problem
A recent study by the United Nations Environment Programme (UNEP) demonstrates that a large part of human exposure to this toxic metal is due to consumption of contaminated fish.
Named the Global Mercury Assessment 2013, the report analysed for the first time the mercury released into the rivers and lakes around the whole world. The small-scale extraction of gold and the combustion of coal for electricity generation seem to be behind the increase in the emissions of developing countries.
As for the sea, in the last century the mercury quantity has doubled in the first hundred meters from the surface of the planet's oceans. Concentrations in deep water have also increased by up to 25%.
To stop the global contamination of this metal, in January more than 140 countries came together in Geneva and approved the start-up of the Minamata Convention, a new international binding regulation bearing the name of the Japanese city where hundreds of people died in the 1950's due to mercury poisoning.
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FECYT - Spanish Foundation for Science and Technology