Trees bear witness to environmental pollution, Swiss study finds

Tree ring chemistry could be used to pinpoint pollution to the year, and trees might one day be used to clean up polluted soil and air. © Keystone / Gaetan Bally

Trees absorb tiny metal particles from the air and soil and store them in their wood, research at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) has found.

This opens possibilities for detecting environmental pollution or even remedying it at some point in the future, according to a WSL press releaseExternal link published on Thursday.

These tiny particles are more than one thousand times thinner than human hair, WSL explains.  They can be pollutants if they consist of toxic heavy metals such as aluminium or lead, or industrial agents that transport active substances.

It was already known that agricultural plants absorb such particles from the environment, but it was not clear if this was also the case with trees. An experiment at WSL has now shown for the first time that intact nanoparticles can pass through the leaves into other parts of the tree.

For their experiment, PhD student Paula Ballikaya and her colleagues sprayed nanoparticles made from gold onto young European beech and Scots pine trees in the laboratory, says the press release. They chose gold particles because they do not harm the trees and are easily detectable in plant tissue. After 20 days, the particles were present not only in the leaves, but also in the trunk and roots.

Tree ring chemistry

The experiment demonstrates that trees absorb nanoparticles, similar to those found in air and water pollution, into their wood. They can still be detected there years later by studying tree rings.

Previous research has detected gaseous pollutants from car exhausts, metal refineries and coal combustion in tree trunks. WSL researchers now suggest extending tree-ring chemistry to environmental monitoring programmes that address nanoparticle contamination.

The study also raises the possibility of using trees to clean up polluted soil and air. “Fast-growing trees could store heavy metals from the soil or air in their wood, which could then be disposed of properly,” says Ballikaya. She stresses that more research is needed.