Soil treatment with plants Birch trees pull microplastics from the ground

According to a study, soil contaminated with microplastic particles can be rehabilitated with the help of trees: experiments have shown that birch trees absorb microplastics from their roots. The problematic particles can then be eliminated with biomass. Further investigations must now show to what extent the process is actually appropriate to combat the pervasive environmental problem.

Torn plastic bags and many other colored rubbish items – it is estimated that one third of all plastic waste ends up in the environment. The ugly remnants of our pariah society are clearly visible in many places. But a large proportion can often only be seen with a magnifying glass or a microscope: Over time, many pieces of waste break down into particles smaller than five millimeters and then partly into nanoparticles of less than 0.1 micrometer in size. The environment is already full of these crumbs and they are carried through the air. Studies show that this civilization signature can indeed be detected in the most remote corners of our planet.

Can tree roots bind particles?

The focus is often on the pollution of water bodies with microplastics, but in some cases it is more pronounced in the soil. An important factor in the spread of agricultural soils is the application of sewage sludge. As a result, fragments of synthetic clothing fibers in particular end up in the soil. Another major contribution is vehicular traffic due to tire wear. Wherever they come in – synthetic little things are a problem: Microplastics can release pollutants that crops may absorb. In addition, the negative effects of microplastics on beneficial soil inhabitants have been shown, and studies have shown that the particles can also provide good opportunities for pathogen development.

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One would think that once the soil is filled with particles, there is no chance of getting them out again. But perhaps there is a way to address it, as results from the current study by researchers led by Kat Austin of the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) give reason for hope. The key word here is phytoremediation – the extraction of pollutants by plants. This method is used to remove toxins from the soil. For this purpose, certain types of plants that absorb these substances well with their roots are transplanted. The biomass can then be disposed of along with the problematic material.

Bearer of hope birch

Studies of wheat and lettuce have already indicated that plants can also bind microplastics. But in their study, Austin and her colleagues have now turned to a woody plant that has already been used successfully in phytoremediation: silver birch (Betula pendula), widespread in Europe. In order to test their ability to absorb microplastics, they cultured test plants in a substrate containing microplastic beads (5 to 50 microns). These particles were labeled with a fluorescent dye for easy detection later in plant tissues. Five months later, the scientists then examined the root samples using confocal and fluorescent laser scanning microscopy.

As it turned out, birch trees had already absorbed particles deep into the root tissues: the researchers were able to detect fluorescent microplastics in different sections and layers of the root system. The percentage of root sections with fertilization was from 5 to 17 percent. The scientists wrote that this indicates that the extraction potential is relatively high, at least in comparison with the indicators of wheat and lettuce. “This pilot study indicates that birch has real potential for long-term soil remediation solutions – including reducing the amount of plastic particles in the soil,” Austin says. Birch also has another interesting aspect: its roots are especially shallow below the surface of the soil, where it is proved that the contamination with microplastics is the highest.

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In order to confirm the potential of birch trees to tackle pollution from geoplastics, the researchers point out, however, that further investigations are necessary. They plan to check intake levels and other aspects more closely. It also needs to be clarified to what extent trees can handle a cleaning function at all: “The rate of uptake of microplastics and the effects on tree health in the short and long term remain to be investigated,” Austin says.

Source: Leibniz Institute for Freshwater Ecology and Inland Fisheries, specialized article: Macro Ecology, doi: 10.1016/j.scitotenv.2021.152085

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