Soils polluted with microplastics could now be cleaned up with the help of trees. For the first time, researchers led by the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) have shown that the slope birch absorbs microplastics through its roots during the growth phase. This is good news, because soils are many times more polluted with microplastics than seas and oceans.
So far, little is known about how microplastics interact with higher-order terrestrial plants. Recent studies have shown that microplastics are taken up in the roots of agricultural plants such as wheat. The IGB and Geoforschungszentrum Potsdam (GFZ) research team has now shown for the first time in an interdisciplinary pioneering project by Berlin-based art studio Studio Austen that longer-lived woody plants such as trees also absorb and store microplastics in their tissues.
Birches are already being used for soil remediation
The hanging birch (Betula pendula Roth.) is already being used to remediate contaminated soil because it can store industrial pollutants and heavy metals in its tissue. Microbes that colonize the trees can then break down the polyaromatic hydrocarbons and heavy metals. In addition, because this tree species roots shallowly below the soil surface, where microplastic pollution has been shown to be highest, the team selected the slope birch for their study.
5 to 17 percent of the root sections studied absorbed microplastics
The researchers labeled microplastic beads (5–50μm) with fluorescent dye and added them to the soil of potted trees. After five months, they examined root samples using fluorescence and confocal laser scanning microscopy. They found fluorescent microplastic in various sections and layers of the root system. The percentage of root sections with microplastic particles ranged from 5 to 17 percent in the experimental trees.
“The uptake rate of microplastics and the effects on the short- and long-term health of the trees still need to be studied. But this pilot study suggests that birch has real potential for long-term soil remediation solutions — including reducing the amount of microplastics in soil and possibly water.”
- Kat Austen, the study’s lead author
2018 study with IGB quantified: Pollution of soils by microplastics greater than in oceans
More than 400 million tons of plastic are produced globally each year. An estimated one-third of all plastic waste finds its way into soils or inland waters as a result. A large proportion of this plastic breaks down into particles smaller than five millimeters, i.e. microplastics, and further into nanoparticles with a size of less than 0.1 micrometers. Microplastic pollution on land is much greater than in the oceans — it is estimated to be four to 23 times greater, depending on the environment.
An important factor in the spread of microplastics is wastewater, for example. 80 to 90 percent of the particles it contains, for example from synthetic clothing fibers, remain in sewage sludge. Most of this is incinerated in Germany. On a global scale, however, it is also partly spread on fields as fertilizer, as a result of which many hundreds of thousands of tons of microplastics end up on and in the soil every year (source: Plastic Atlas 2020). This is why microplastic concentrations on field soil are also particularly high — just as they are on roadsides, because tire abrasion is another significant source of microplastics.
