According to an interdisciplinary pilot study headed by the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) and the German Research Centre for Geosciences in Potsdam (GFZ), birch trees could help to remediate soil contaminated with microplastic. In the journal "Science of the Total Environment", the research team reports that, during the growth phase, the trees filter microplastic from the water in their vicinity and can store it in their roots.
The research team, headed by Kat Austen from the IGB, wanted to know on the one hand how soil contaminated with microplastic affects long-living plants such as trees. On the other, the researchers wanted to analyse whether trees have the potential to decontaminate soil that has been polluted with microplastic. For their study, the research team selected the silver birch (Betula pendula Roth). It forms flat roots just below the surface of the soil. There, according to the present state of knowledge, the microplastic concentration is at its highest. This type of tree is also already being used for soil remediation because the trees are able, as previous studies have shown, to absorb industrial substances like heavy metals from contaminated soil and break them down. For the study, the research team tagged microplastic beads of polyamide (PA) with a diameter of 5 to 50 µm with fluorescent dye. They mixed 3 g of microplastic into 15 litres of soil, in which two one-year old birch saplings were planted. The concentration of microplastic to soil falls within the range of environmentally observed microplastic concentrations. After five months, the scientists took samples from the roots and examined them with various microscope techniques. In 6 out of 64 root sections, tagged microplastic particles were found with a size of less than 10 µm in various areas and layers of the root system right into the inside of the roots. The percentage of tree root sections in which microplastic particles were observed in the two trees was 15-17 percent. It was not possible to exactly determine in the study at which points of the root system the microplastic had been taken up. The previously proven uptake of smaller particles below 10 µm was interpreted by the research team as an indication that the particle size is a limiting factor in the take-up of microplastic.
They also suspect that the plastic particles get into the plants via the root tips or through cracks. "The rate of uptake of microplastic and the effects on the short and long-term health of the trees warrants further study. However, this pilot study indicates that the birch tree has genuine potential for long-term solutions for soil remediation – including a reduction in the quantity of microplastic in the soil and possibly in the water," says Kat Austen, the chief author and project coordinator at the IGB, summarising the results of the study.
Further information: go to the study "Microplastic inclusion in birch tree roots"