How Micro-Plastics Impact Plant Health and Our Food

By Nina Hunt, Herbarium Intern, Royal Botanical Gardens.

Scientists estimate that one third of all plastic waste ends up in soils and freshwater. Most of this plastic breaks into pieces smaller than 5 mm, also known as microplastics. The negative impacts of microplastics on fish has become a well researched topic — but what about the plastic that doesn’t end up in our water? Microplastics found in plastic coatings and linings, biodegradable plastics, and other litter end up in the soil plants grow in. In fact, plastics in land ecosystems are even more extensive than in aquatic ecosystems (1). This problem is a growing concern and researchers are now investigating the impacts of microplastics on plant health.

Studies show that microplastics change soil structure and composition, which impacts plant health. This includes decreasing density, increasing acidity, and disrupting nutrient cycling (1). Microplastics also have a large impact on soil microbe communities by increasing microbial growth (1-2). This means that microbes take up nutrients that plants could otherwise use (1).

Microplastics in the soil go on to plant biomass, delay germination of seeds, and decrease cell survival (3-5). How exactly this happens is unknown, though there is evidence that microplastics accumulate around the root tips (6).

Given the size of microplastics, scientists assumed that microplastics are too large to be taken up by plant cells. But two studies published last year seem to counter this assumption. Shockingly, one study discovered microplastics within the tissues of edible fruits and vegetables. Carrots were the vegetable with the highest microplastic content, while apples were the fruit with the highest content (7).

To explain this, researchers predict a novel way that microplastic enter roots and may travel to other areas of the plant (8). They call this the “crack-entry model”, where openings between root cells take up plastic particles. Some microplastics are later found in the above ground plant, suggesting transport from the roots to the stem (8).

Microplastics in soils clearly pose an enormous threat to our ecosystems, agriculture, and human health. It is important to keep in mind that the plastics we use (even those labelled “biodegradable”) can break down into microplastics. Reducing singe-use plastics, choosing glass and metal alternatives, or using reusable products help reduce the microplastics that end up in our soils. By reducing our own plastic waste, we can support the plants, the biodiversity, our own health, and the health of our planet.

Primary header photo courtesy of 5Cyres, 2012, FlickrCommons. CC BY-SA 2.0.

References

1. Iqbal, S., Xu, J., Allen, S.D., Khan, S., Nadir, S., Arif, M.S., Yasmeen, T. 2020. Unraveling consequences of soil micro- and nano- plastic pollution on soil-plant systems. Chemosphere 260, 127578.
2. Zang, H., Zhoi, J., Marshall, M.R., Chadwick, D.R., Wen, Y., Jones, D.L. 2020. Microplatics in the agroecosystem: Are they an emerging threat to the plant-soil system? Soil Biology and Biochemistry 148, 107926.
3. Bosker, T., Bouwman, L.J., Brun, N.R., Behrens, P., Vijver, M.G. 2019. Microplastics accumulate on pores in seed capsule and delay germination and root growth of the terrestrial vascular plant Lepidium sativum. Chemosphere 226, 774e781.
4. de Souza Machado, A.A., Lau, C.W., Kloas, W., Bergmann, J., Bachelier, J.B., Faltin, E., Becker, R., Gorlich, A.S., Rillig, M.C. 2019. Microplastics can change soil properties and affect plant performance. Environmental Science and Technology 53, 6044e6052.
5. Kalcíkov a, G., Gotvajna, A.Z., Kladnik, A., Jemec, A. 2017. Impact of polyethylene microbeads on the floating freshwater plant duckweed Lemna minor. Environmental Pollution 230, 1108e1115.
6. Taylor, S., Pearce, C.I., Sanguinet, K.A., Hu, D. 2020. Polystyrene nano- and microplastic at Arabidopsis and wheat root cap cells but no evidence for uptake into roots. Environmental Science: Nano. 7,7.
7. Conti, G.O., Ferrante, M., Banni, M., Favara, C., Nicolosi, I., Cristaldi, A., Fiore, M., Zuccarello, P. 2020. Micro- and nano-plastics in edible fruit and vegetables. The first diet risks assessment for the general population. Environmental Research 187, 109677.
8. Li, L., Luo, Y., Li, R., Zhou, Q., Peijnenburg, W.J.G., Yin, N., Yang, J., T, C., Zhang, Y. 2020. Effective uptake of submicrometre plastics by crop plants via a crack-entry mode. Nature Sustainability 3, 929-937.