Researchers at the University of Burgos in Spain have developed a portable and inexpensive new method of detecting levels of mercury in water. The simple test uses a sheet that changes color when inserted into mercury-contaminated water, with results visible to the naked eye.

The membrane uses a dye called rhodamine, a florescent organic compound, to indicate the presence of mercury. "Rhodamine is insoluble in water," says José Miguel García, one of the researchers involved in the project. "But we chemically fixed 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 method requires no technical expertise and involves placing the membrane in the water for five minutes. If it contains mercury, it will turn red.

The composition of the sheet can be adjusted to specific parameters. The Spanish researchers used the U.S. Environmental Protection Agency standards for reference, which is 2 ppb (parts per billion) of divalent mercury in water for human consumption.

For a more detailed visualization, the user can photograph the sheet with a mobile phone or tablet computer. This can then be compared with reference values to quantify the level of mercury in the sample being analyzed using imaging software such as the open-source program GIMP.

Existing methodologies to measure mercury contamination are complex and costly. It usually involves sending samples to a laboratory that needs to be fitted with very expensive analysis equipment.

Mercury ingested by humans accumulates in the brain and the kidneys, leading to related health problems. The new analysis method developed in Spain coincides with recent global efforts to tackle growing concerns over mercury pollution, caused mainly by mining activities.

In January, 140 country representatives gathered in Geneva to negotiate details of the Minamata Convention, a legally binding treaty named after the Japanese city where hundreds of people died in 1956 due to mercury contamination from untreated chemical factory waste water.

The Minamata Convention provides control and reduction systems that cover a wide range of activities and products where mercury is involved. The document will be finalized in October.

Details of the new mercury test sheet have been published in the journal Analytical Methods.