With the help of trees, microplastic-polluted soils could be remediated.
A recente study [1] has shown that birch trees absorb microplastics through their roots during the growth phase. Good news, because soils are many times more polluted with microplastics than oceans are.
So far, little is known about how microplastics interact with higher-order terrestrial plants. Microplastics are taken up in the roots of agricultural plants such as wheat but for the first time it was shown that longer-lived woody plants absorb and store microplastics in their tissue.
It is known that birch trees can be used for phytoremediation because they sequester and store industrial pollutants and heavy metals in their tissues, which subsequently allows the colonisation of microbial communities that breakdown polyaromatic hydrocarbons. This tree species’ roots grow close to the soil surface, where microplastic pollution has been shown to be highest, making them a good choice for the study.
The researchers [1] labelled 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 different sections and layers of the root system. The percentage of root sections with microplastic particles ranged from 5 to 17 per cent 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. This pilot study suggests birch has real potential for long-term soil remediation solutions, including reducing the amount of microplastics in soil and possibly water [1,2].
Over 400 million tons of plastic are produced globally each year. It is estimated that one third of all plastic waste ends up in soils or freshwaters. Most of this plastic disintegrates into particles smaller than five millimetres, referred to as microplastics, and breaks down further into nanoparticles, which are less than 0.1 micrometre in size [2]. In fact, terrestrial microplastic pollution is much higher than marine microplastic pollution – an estimate of four to 23 times more, depending on the environment [1]. Sewage, for example, is an important factor in the distribution of microplastics.
Sewage could be incinerated but sometimes it is also partly applied to fields as fertilizer, meaning that microplastics end up in our soils each year [2]. This is why the microplastic concentrations on field soil are also particularly high, just as they are on roadsides, because tyre abrasion is another significant source of microplastics.
This new study coul be of interest to enhance phytoremediation projects where birch trees can perfectly grow.
[1] Microplastic inclusion in birch tree roots; Kat Austen, Joana MacLean, Daniel Balanzategui, Franz Holker; Science of the totale environment, Vol 808, 20 February 2022, 152085
[2] https://www.fv-berlin.de/en/info-for/the-media-and-public/news/birch-trees-remove-microplastics-from-the-soil
