Worms, microplastics and nanoplastics

By Yun Son

Garden worms play an extremely vital role despite its small size. The presence of worms is an indicator of  soil quality;  healthy, moist soil will have more worms, whereas  dry, poor, infertile soil will show no signs of worms. 

Darwin himself was absolutely fascinated by earthworms and their behaviour in soil. He conducted an experiment on earthworms lasting 40 years, in his own garden, and published a book on their behaviour in 1881 (The Formation of Vegetable Mould Through the Action of Worms). (Science Learning Hub, 2012) Essentially, worms consume soil and excrete important nutrients and minerals via their waste, thus, playing a central role in soil health. (National Geographic Society, n.d.) Unfortunately, in recent years, this behaviour has started to have negative impacts on both itself and its surroundings, due to the growing issue of microplastics and the formation of nano plastics. 

Microplastics, as can be inferred from its name, are small plastic particles, usually less than 5 millimetres in diameter. These microplastics have started to infiltrate many water reserves, oceans, and soil. 

There are 2 types of microplastics: primary and secondary. Primary microplastics are commercial products, often found in cosmetics, microfibres, textiles, fishing nets, etc. Secondary microplastics are produced from the disintegration of larger particles by solar radiation and ocean waves. As littering and the use of single-use plastics increases over the globe, environmental pollution and the amount of microplastics found in the environment grow too. Plastics take thousands of years to be decomposed into harmless particles. With its minuscule size, animals, including humans, are constantly consuming microplastics. (National Geographic Society, 2019)

Microplastics is a term that most people have heard, though some people do not understand what it means. Nanoplastics, on the other hand, is a less familiar term. The term is still under debate, as to what qualifies as a nanoplastic. Generally, nanoplastics are defined as plastic particles less than 100 nanometres in diameter, although this definition can change depending on the context. (Gigault et al., 2018) 

A recent study conducted in South Korea, revealed that microplastics in the soil had negative impacts on worms. Two important observations were made: firstly, the research team found that microplastics had negative impacts on the reproductive systems of these soil organisms, and secondly, worms that consumed these microplastics produced nanoplastics via biological fragmentation. In more detail, by exposing the earthworms Eisenia Andrei to microplastics, they were able to learn that this exposure damaged coelomocyte viability and male reproductive organs. The fragmentation of microplastics to nanoplastics by the earthworms were proved by using scanning electron microscopy and energy dispersive X-ray analysis. (Kwak & An, 2020) 

These impacts on earthworms by microplastics are concerning as worms are important actors in the soil. They have vital roles in providing essential nutrients to other organisms, especially plants. The fact that their reproduction and growth are disrupted, could lead to many problems to the entire ecosystem. Although the exact consequences of bioplastics on humans and health is not exactly known yet, studies on the impact of microplastics on animals generally point to the negative side. Thus, it seems reasonable to find ways to reduce microplastics production and to further research on the consequences that these may have on human health.

References:

Science Learning Hub. (2012) Charles Darwin and earthworms. Available from: https://www.sciencelearn.org.nz/resources/22-charles-darwin-and-earthworms [Accessed 14th November 2020]

National Geographic Society. (n.d.) Common Earthworm. Available from: https://www.nationalgeographic.com/animals/invertebrates/c/common-earthworm/ [Accessed 14th November 2020]

National Geographic Society. (2019) Microplastics. Available from: https://www.nationalgeographic.org/encyclopedia/microplastics/ [Accessed 16th November 2020]

Gigault, J., Halle, A., Baudrimont, M., et al. (2018) Current opinion: What is a nanoplastic? Environmental Pollution. 235, 1030-1034. Available from: https://www.sciencedirect.com/science/article/abs/pii/S0269749117337247 [Accessed 16th November 2020]

Kwak, J., & An, Y. (2020) Microplastic digestion generates fragmented nanoplastics in soils and damages earthworm spermatogenesis and coelomocyte viability. Journal of Hazardous Materials. 402. Available from: https://www.sciencedirect.com/science/article/abs/pii/S0304389420320240

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