Waters of Rio Tinto river, in Andalusia, Spain. Very known for being very acidic (pH 2) and its deep reddish hue due to iron dissolved in the water. Rio Tinto has scientific interest due to the presence of extremophile anaerobic bacteria that dwell in the water. The subsurface rocks on the river bed contain iron and sulfide minerals on which the bacteria feed. The subsurface rocks on the river bed contain iron and sulfide minerals on which the bacteria feed. NASA scientists have also directly compared the chemistry of the water in which the rocks of Mars planet were deposited in the past with the Río Tinto. Likewise Jupiter's moon Europa is theorized to contain an acidic ocean of water underneath its ice surface. Thus the river is of interest to astrobiologists. Highly acidic environments are relatively scarce worldwide and are generally associated with volcanic activity and mining operation. Río Tinto is an unusual ecosystem due to its size (100 km long), rather constant acidic pH (mean value 2.3), high concentration of heavy metals (Fe, Cu, Zn, As, Mn, Cr, etc.) and high level of microbial diversity.

Javier Montero