Mine-grown moss shows unusual power to trap toxic metals from water without energy

Toxic metals are seeping into northern waterways at a faster pace as climate change alters soils and drainage patterns. In Finland, researchers now say an unlikely ally may help slow that flow. A common moss, backed by microscopic partners living inside it, has shown a rare ability to pull metals from polluted water without energy or chemical treatment.

Researchers at the University of Oulu say the system could offer a sustainable alternative for sites where conventional treatment fails. Cold temperatures, remote locations, and abandoned infrastructure often limit traditional water purification methods. Forest ditching and old mine sites also continue to release metals into nearby streams. The team focused on Warnstorfia fluitans , a moss species discovered thriving in acidic, metal-rich waters.

Scientists first spotted dense growths near the Pyhäsalmi Mine in Finland. Few other plants survive in such conditions, where high acidity increases metal solubility and toxicity. Moss thrives in mines The moss did more than survive. It flourished in water loaded with dissolved metals.

That observation triggered deeper investigation into how the plant copes with extreme chemistry. 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 examined how gold accumulates in spruce needles and how microbial diversity varies between northern and southern Finland.

That work helped shape the new study s direction. The research revealed that mosses do not remove metals alone. The process depends on close cooperation between the plant and microbes living inside its tissues. These microbial partners, known as endophytes, were more abundant in mosses collected from metal-contaminated waters.

Two species stood out: Phialocephala bamuru and Hyaloscypha hepaticola . Both appeared frequently in mosses from polluted sites. Researchers also grew both species successfully in laboratory conditions. The results suggest these microbes help mosses handle dissolved metals by altering internal chemical conditions.

This process allows metals to precipitate and become less harmful. 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. These metals pose long-term risks to ecosystems and water quality. From mines to forests The project involved international partners and industry collaboration with Pyhäsalmi Mine and steel producer Outokumpu. Researchers also collected moss samples from the closed Saattopora Mine in Finland and the Adakgruvan Mine in Sweden.

They compared mosses from metal-rich waters with those from clean environments. Previous tests showed that mosses can remove nutrients from water within three weeks. Metal removal takes longer and may require several weeks. Ongoing research aims to measure efficiency under different conditions.

Pirttilä s group is also exploring commercial uses. We are developing microbial strains and products for use across different sectors, she says. The team will next test moss-microbe purification in iron-rich forest drainage ditches. The trials will take place in the Kalimenjoki catchment near Lake Jäälinjärvi in northern Finland.

In forest drainage management, mosses should not be seen as debris that blocks water flow, Lehosmaa emphasizes. Instead, the researchers see mosses as active partners in cleaning polluted northern waters. The study is published in the journal iMetaOmics.