Chemists at the University of Burgos (Spain) have manufactured a sheet that changes colour in the presence of water contaminated with mercury. The results can be seen with the naked eye but when photographing the membrane with a mobile phone the concentration of this extremely toxic metal can be quantified.
Mercury contamination is a problem that is particularly affecting developing countries. It poses a risk to public health since it accumulates in the brain and the kidneys causing long term neurological illnesses. It is emitted from industrial and mining waste, especially small-scale gold mining.
A team at the University of Burgos have now developed a technique for detecting the presence of this dangerous metal in water "in a cheap, quick and in situ way," as explained to SINC by Jos- Miguel Garc-a, one of the authors of the study. Details have been published in the 'Analytical Methods' journal.
The method consists of placing the fine sheet created by the researchers in the water for five minutes. If it turns red, this signals the presence of mercury. "Changes can be seen by the naked eye and anyone, even if they have no previous knowledge, can find out whether a water source is contaminated with mercury above determined limits," outlines the lecturer Garc-a.
In addition, if we take a photograph of the sheet with a digital camera, like those in mobile phones or tablet computers, we can find out the concentration of the metal. We only need image treatment software (the team used the open access GIMP programme) to see the colour coordinates. The result is then compared with reference values.
The membrane contains a florescent organic compound called rhodamine, which acts as a mercury sensor. "Rhodamine is insoluble in water," says the researcher. "But we chemically fix it to a hydrophilic polymer structure in such a way that when put into water it swells and the sensory molecules are forced to remain in the aqueous medium and interact with mercury."
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.