Eldorado for science
The smallest of all living things fascinates the professor of geomicrobiology. He explores how minerals and microorganisms, especially bacteria, interact with each other. At Río Tinto, experts like him can access a unique natural laboratory that attracts researchers from around the world. Iron mineral deposits and extreme conditions in the region are similar to the surface of Mars and NASA has even tested equipment and analytical methods for finding traces of life on Mars here.
Metals such as iron, copper, lead, zinc and nickel remain dissolved in the water in their individual components due to the high acid concentration – normally they form solids and settle as sediments. It is estimated that up to 15 percent of the metal ions that are washed into the oceans worldwide come from the Río Tinto: Individual metal particles that carry an electrical charge and play an important role in chemical and ecological processes.
“The Río Tinto is one of the first areas where biomining has helped extract copper from ores,” says Kappler. “Even the Romans noticed that copper was released from the ores into the river water. Today we know that this is thanks to bacteria.” Many expeditions by plane and minibus have been made from Tübingen to the Río Tinto to gain insights for projects in basic geoscientific research. Researchers from the Autonomous University of Madrid also help with the work on site. The collected samples are then safely packaged and sent to the Tübingen laboratory.
“We are interested in what’s happening under the ground,” says Kappler. There is plenty of the mineral pyrite, also known as fool’s gold, in the region. Bacteria like Acidithiobacillus ferrooxidans, oxidize fool’s gold, dissolving it into its components of iron and sulfur. This results in a sulfuric acid solution, which in turn flushes iron and other metals (cobalt, manganese, nickel, cadmium) out of the rock and transports them into the river together with rainwater. “We are investigating which microorganisms play a role in this, how active they are under these extreme conditions and which of them can be found in the river and sediment.”
In 2020, Kappler, Sara Kleindienst and other researchers investigated which food the microorganisms in the Río Tinto metabolize and how they influence the transport of heavy metals to the estuary. While some minerals dissolve completely, the river transports others in the form of nanoparticles towards the sea. There, the metal ions of microorganisms, plankton, fish and higher organisms are used in enzymes or are deposited in sediments. “If we understand the transport processes, we can also better assess the impact on the environment and people.”
