New research led by the Leibniz Institute for Freshwater Ecology and Inland Fisheries shows that individual microplastic particles with diameters between 5 and 10 μm can enter the root system of the silver birch (Betula pendula), a species of tree native to Europe and parts of Asia, from the surrounding soil.

Longitudinal cross-section showing microplastic particles inside a birch lateral root in a one-year-old birch tree after being exposed to contaminated soil for 5 months. Clockwise from top left shows cross sections using light microscopy, fluorescence microscopy, and confocal laser scanning microscopy. Arrows point to fluorescing microplastic particles. Inset in bottom right panel shows the area indicated by the arrows in the bottom left panel after enlargement. All images have been enhanced using a contrast and brightness correction. Scales are shown in the bottom right or left corner of the respective image. Image credit: Austen et al., doi: 10.1016/j.scitotenv.2021.152085.

“Birch trees have been used to remediate contaminated land by sequestering and storing industrial pollutants in their tissues, which subsequently allows the colonization of microbial communities that breakdown polyaromatic hydrocarbons and heavy metals,” said lead author Dr. Kat Austen from the Leibniz Institute for Freshwater Ecology and Inland Fisheries and her colleagues from Germany.

“Common across temperate Eurasian and North American landscapes, birch trees rapidly colonize and stabilize disturbed land allowing for reforestation.”

“Because the species’ dense root system lies near the soil surface where the concentration of microplastic pollution has been shown to be highest, the motivation for this study was, can birch trees offer phytoremediation of plastic-pervaded soils by the direct uptake of microplastic particles?”

In the study, the authors labeled microplastic beads with fluorescent dye and introduced them to the soil of potted silver birch trees.

After five months, they examined root samples using fluorescence- and confocal laser scanning microscopy.

A total of 64 root sections was examined, in 6 of which it was possible to detect between one and four microplastic particles, with a median of one.

The percentage range of tree roots sections in which microplastic particles were observed over the two experimental trees was 5–17%.

“The results demonstrate that the uptake and storage of microplastics in birch trees warrants further study,” they said.

“For instance, indications from wheat and lettuce studies exposed to smaller particle sizes of 0.2-2 μm suggest that rates of microplastic inclusion in the submicrometer size range in birch tree roots may be significantly higher.”

“The inclusion of microplastic beads into the root tissue gives a positive indication that other micro-and nano-sized particles arising from the breakdown of plastics in the environment could be incorporated into tree roots.”

“Depending upon further study into the rate of uptake and its effect on short- and long-term tree health, and given the remediation potential of birch for other soil-based pollutants, we posit the potential of birch for long-term soil remediation solutions.”

“Our findings lay the foundation for investigation of the role of birch trees in phytoremediation not only for sites with chemical contamination, but now also for those with substantial microplastic pollution.”

The study was published in the journal Science of The Total Environment.

Kat Austen et al. 2022. Microplastic inclusion in birch tree roots. Science of The Total Environment 808: 152085; doi: 10.1016/j.scitotenv.2021.152085