Detecting mercury contamination in water with a mobile phone
07 February 2013
Chemists have developed a 'litmus paper' test for mercury contamination in water, but a mobile phone photograph of the test is able to provide an accurate measurement of concentrations.
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 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.
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.
However, if a photograph of the sheet is taken with a digital camera, like those embedded in mobile phones or tablet computers, the concentration of the metal can be determined. Image treatment software (the team used the open access GIMP programme) is then applied to see the colour coordinates. The result is subsequently compared with reference values.
The sheet contains a fluorescent organic compound called rhodamine, which acts as a mercury sensor. Rhodamine is insoluble in water, but the researchers 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 US Environmental Protection Agency are exceeded: 2 ppb (parts per billion) of divalent mercury –Hg(II) - one of the most reactive - in water destined for human consumption.