New findings shed light on the mechanisms behind a natural purification process and identify the key microbial “teammates” that enable mosses to remove metals from water. A promising moss species was discovered in abandoned mine sites where few other plants survive. Upcoming tests will evaluate their performance in iron-rich forest drained ditches.
Across northern regions, climate change is accelerating the release of metals into waterways. Forest ditching and abandoned mines also leave behind sites that need sustainable water purification solutions. Conventional water treatment methods often fail in cold environments. Researchers at the University of Oulu, Finland are therefore developing alternative, nature-based purification systems that operate without energy input and function reliably in remote conditions.
The project began when researchers discovered abundant stands of Warnstorfia fluitans moss growing in acidic, metal-laden waters near the Pyhäsalmi Mine in Finland. To their surprise, the moss appeared to flourish in conditions where high acidity increases metal solubility.
“Growing evidence shows the crucial role of microbes in helping plants to survive in extreme environments,” explains Professor Anna-Maria Pirttilä. Her research group has previously studied, for example, how gold accumulates in spruce needles and how microbial diversity in bilberries varies between northern and southern Finland.
The new study reveals that mosses do not remove metals alone. The key is the cooperation between the moss and its microbial symbionts.
Microbes live in all organisms, and those inhabiting plants in symbiosis are called endophytes. Mosses collected from metal-rich sites hosted more endophytes that enhance metal tolerance. Two species stood out: Phialocephala bamuru and Hyaloscypha hepaticola, both abundant in metal-contaminated waters. Both were also successfully cultivated in the laboratory.
The results suggest that these symbionts help mosses to precipitate dissolved metals inside their cells. “The moss acts like a sponge that binds and transforms metals into a safer, solid form,” says Postdoctoral Researcher Kaisa Lehosmaa. “The microbes modify conditions inside the moss tissue so that harmful dissolved metals can be converted into manageable particles. And there is always a possibility to remove metal-rich mosses.” The study examined iron as well as cadmium, copper, zinc, nickel, and arsenic.
The research, carried out with international partners, involved collaboration with Pyhäsalmi Mine and Outokumpu steel producer. Moss samples were also collected from the closed Saattopora Mine in Finland and Adakgruvan Mine in Sweden. Mosses from metal-rich waters were compared with those from clean environments.
Pirttilä’s group is also exploring commercial applications. “We are developing microbial strains and products for use across different sectors,” she says.
Previous tests have shown that mosses can remove nutrients from water within three weeks. Metal removal is estimated to take several weeks, and ongoing research aims to evaluate purification efficiency further.
“In forest drainage management, mosses should not be seen as debris that blocks water flow,” Lehosmaa emphasizes. The team will next test moss-microbe purification in the iron-rich Kalimenjoki catchment near Lake Jäälinjärvi in northern Finland.
The study, “Aquatic moss precipitates metals in the presence of a specific endophytic microbiome,” was published in October 2025.
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