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Nanoplastics influence microbial activity in the soil

Micaela Mafla-Endara in the lab. Photo.
Micaela Mafla-Endara and one of her 'hotels' for soil organisms. Photo: Anna Maria Erling

Remnants of plastic left by humans can now be found practically everywhere in nature – in waterways, within animals, and even amidst the clouds. In her thesis, Micaela Mafla-Endara examined how nanoplastics that end up in the soil affect the microorganisms living there. The answer is clear: there is an effect on the organisms and how they behave.

One could say that Micaela Mafla-Endara and her team have developed a window to the underworld with the help of micro-engineered techniques. An opening that allows Micaela to peek inside and study what happens there, beneath the surface, amidst the multitude of organisms crucial for the soil. Specifically, she has investigated how microorganisms in the soil are influenced by the presence of nanoplastics, small nanoparticles originated from the plastic that we humans spread in nature. After several studies, she has found that plastic impacts the behavior of microorganisms.

"It's important to acknowledge that plastic waste that ends up in the soil affects the whole system," she says.

Transparent chips as microhabitats

Studying the habitat of microorganisms in dark and opaque soil is not easy. As a part of her doctoral work at the Center for Environmental and Climate Science (CEC), Micaela has worked on developing a method to make it possible – the so-called window to the underworld. She used transparent chips as microhabitats or 'hotels' for soil organisms, enabling observations through microscopy. The microorganisms she studied include bacteria, fungi, protists, and small nematodes, which collectively play a vital role in the ecosystem by enhancing soil stability and fertility.

In the next phase, she conducted several studies where microorganisms were exposed to nanoplastics, and the results showed that microorganisms interact with nanoplastics, either by ingesting the plastic particles or by the plastic particles adhering to the microorganisms.

"This interaction disrupts how microorganisms typically behave and organize themselves as communities," says Micaela Mafla-Endara.

The effect various with the organisms

Regarding the general effect this might have on our soils, she hesitates to answer completely, as her research operates on a microscale. However, she believes that soil quality could be negatively affected. The effect of plastic particles on various organisms varies. While some microbial groups are not affected, others seem to temporarily increase in number, and others suffer adverse consequences, such as decreased biomass. This means that the diversity and composition of species in the soil are disturbed – some species may even disappear entirely – which could affect nutrients and soil health. Micaela Mafla-Endara therefore urges caution when it comes to plastic and plastic waste.

"We humans do not always see the consequences of our behavior, in this case, the amount of plastic we use and where it ends up. Stricter regulations and greater awareness of the actual impact plastic can have on the environment are crucial. We depend on the soil for our survival, and there is a lot of uncertainty about how harmful it can be," she says.

The 'vacuum' effect

Plastics often contain a range of chemical additives that can be toxic. And the problem with plastic particles ending up in the soil is that they can remain there for decades. When Micaela Mafla-Endara and her supervisor, Edith Hammer, published a study last autumn showing that a fungus 'vacuums' nanoplastics from its surrounding, it attracted a lot of attention (see links below).

"They clean the environment, leaving free space for the same microorganism to continue growing," says Micaela Mafla-Endara, suggesting that the phenomenon should be further explored to see if it can be used for bioremediation – the removal of pollutants through organisms.

Overall, she hopes that her work can shed light on an often-overlooked aspect of the environment – life in the soil – and that more people will become aware of the complexity when nanoplastics interact with microorganisms and soil ecosystems. 

“This is something that could also be relevant to consider in decision-making and policy processes”, she says.

Vacuum cleaner-effect in fungi can hold nanoplastics at bay | Lund University

Exposure to polystyrene nanoplastics reduces bacterial and fungal biomass in microfabricated soil models - ScienceDirect