Forest trees

Forest trees absorb nanoplastics, research finds

Image credit: Lane Erickson/Dreamstime

A laboratory study shows that forest trees take up plastic particles through their roots and transport them to the above-ground tissues of the plant.

A research study by the Swiss Federal Institute for Forest Snow and Landscape Research WSL published in iForest has found evidence that forests can absorb plastic articles

The impact of this on the food chain is still unclear.

It has been estimated that humans ingest about five grams of plastic every week, equivalent to about half a rice bowl, according to Reuters. However, this new data might alter those calculations.

Plastic waste is now polluting all of the world's ecosystems, even those located far from civilisation. The increase in use of single-use plastics to reduce Covid-19 infection rates alone has generated an estimated 8.4 million tonnes of plastic waste generated from 193 countries since the start of the pandemic.

Plastic is extremely slow to decompose. According to the German Nature and Biodiversity Conservation Union, a plastic bag takes 10 to 20 years, a plastic straw 200 years and a plastic bottle 450 years to decompose. During decomposition, these objects are ground into ever-smaller particles over time. These are known as microplastics (particles smaller than 5mm) or nanoplastics (particles smaller than 1,000nm).

Nanoplastic particles in particular pose a potential hazard to living organisms, as these can absorb the particles. The particles accumulate in the tissue and there are indications that they can cause chronic inflammation.

Only a handful of studies have as yet been conducted into whether plants absorb nanoplastics via their roots, with no studies focusing on forest trees. Previous studies on onions point to nanoplastics being able to damage root cells and thus inhibit root growth.

The research team led by Arthur Gessler from the WSL Ecosystem Ecology Group, has investigated the uptake of nanoplastics in three common species of forest tree, namely birch, spruce and sessile oak. The researchers labelled polystyrene nanoparticles measuring 28nm  with the heavy carbon variant 13C and added them to water, which was then administered to the lower roots of tree seedlings.

Using this method, the team was able to detect 13C in the plant tissue after one to four days, mostly in those parts of the roots in direct contact with the water mixed with nanoplastics. However, small amounts of nanoplastics also accumulated in the upper parts of the roots and in the leaves. In the birch, which consumes large volumes of water, significant amounts of nanoplastics were also deposited in the trunk.

The researchers' theory is that nanoparticles are transported via the xylem, the vessels that move water around the plant.

Although the amount of plastic absorbed by the trees analysed is small, it could still have serious repercussions in the global food chain.

"If trees are exposed to these concentrations for years on end, we can definitely expect that significant volumes will be transported to and consequently accumulate in the leaves, trunk and branches," Gessler explains.

The team is now conducting further experiments to determine whether nanoplastics interfere with photosynthesis, more specifically the photochemical reaction of the seedlings, and consequently affect plants' nutrition. Gessler believes that only by banning single-use plastic packaging wherever feasible and recycling as much as possible can we solve the problem posed by plastic.

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