Plastic pollution: Plants fight back!

Having published a piece about plastics recently, I was not expecting to pen another one quite so soon. But, plastic pollution is a major and persistent problem on our planet – on the land (Xiao Chang et al.), in the sea (Bethany Clark et al.), in rivers (William de Haan et al.), lakes and reservoirs (Veronica Nava et al.), in the air (Janice Brahney et al.), and even moves from the ocean into the atmosphere (Isabel Goßmann et al.) – and there’s no sign of it going away any time soon. It would be lovely if we could just wave a magic wand and make it all disappear. Since we can’t do that, it’s nice to have a bit of good news, and hear of a novel approach that might help to reduce this scourge of the modern age. Although it’s not exactly a magic wand, nor a sprinkling of fairy dust to make the problem fly away, it is hoped that good old-fashioned dust from wood – ‘sawdust’ – may help to remove some of this burden.

Using sawdust treated with tannic acid (Mathew Pregasen), Yu Wang et al. have developed a filter that can remove a wide range of nano- and microplastics [NMPs]* from water. Known as bioCap, this biofilter is reported as being highly efficient and able to deal with polyethylene terephthalate [PET], polyethylene, polystyrene, polymethyl methacrylate, polypropylene, and polyvinyl chloride [PVC]. Furthermore, preliminary study using mice suggests that the filtered water may be sufficiently plastic pollutant-free to pose little risk of tested NMPs accumulating in body organs of mammals – such as humans. Although much more work will be needed to scale-up this technology, it’s certainly promising. But, as a Botanist, writing for a botanically-curious audience, it would be really useful to know from what plant(s) the sawdust came. Unfortunately, we are only told that “Residual wood sawdust (lateral dimensions of 30–150 μm and length up to 500–2,000 μm) was secured from Shuolong Co., Ltd (China)”. Pity.

Much of the bad press surrounding plastics comes from the use of fossil fuels such as oil, coal or natural gas (Payal Baheti) in the manufacture of these man-made malevolent materials – either as energy sources required to power their synthesis or as a source of raw materials from which the plastics are made. One way to avoid some of that problem is to manufacture bioplastics (P Prasteen et al.; Ghada Atiwesh et al.; Dina Al-Khairy et al.), which are made from non-fossil fuel-derived sources such as plants. Bioplastics is the approach employed by Hareesh Iyer et al., using spirulina [Arthrospira spp.], a blue–green alga. More accurately called a cyanobacterium (Kartik Aiyer), spirulina is therefore a prokaryote (Nicole Gleichmann), an organism that is about as unlike-a-plant-as-you-can-get. However, its possession of photosynthetic properties and pigments akin to those of true algae and ‘proper’ plants naturally justifies its inclusion in a plant-based blog item. Right, now we’ve got that out of the way, back to the story…

Apparently, the bioplastic is made from applying heat and pressure, without the use of any binders or additives, to intact spirulina cells that have been harvested and dried. In the authors’ own words, “a fast, simple, and scalable process is presented to transform raw microalgae into a self-bonded, recyclable, and backyard-compostable bioplastic with attractive mechanical properties surpassing those of other biobased plastics such as thermoplastic starch”. As exciting as all of that sounds,** it’s early days for this bioplastic, and there are still issues to overcome before it is commercially viable. For example the plastic is considered too brittle at present to be of much use, and it is sensitive to water – “You wouldn’t want these materials to get rained on”, Iyer is reported as saying (Sarah McQuate). Which is not the best news if you were considering using such bioplastic cutlery outdoors for a picnic or dining al fresco during the British summer we’ve just endured in July and August 2023 (Gurj Nanrah; Ben Rich & Sarah Keith-Lucas)(!)*** Nevertheless, avoiding some use of fossil fuels, and creating a plastic that breaks down without any special treatment and which “leaves no microplastic behind” (Rob Waugh), sounds like the definition of a ‘win–win’.

* Nano-/microplastics (NMPs), range from small (<1 μm) to large-sized (<5 mm) organic colloidal matter, and are products of the gradual erosion, fragmentation, and liberation of plastics (Yu Wang et al., 2023).

** ‘Hyped’ as being a new plastic that “turns into compost as quickly as a banana peel” (Rob Waugh), I wonder if that has been fully thought through as a USP? Notoriously, banana skins [or peels] can take years to break down if discarded into the natural environment (Jane Hemphill) [although the notion of two years has been challenged, and needs appropriate qualification if used as a ‘fact’]. And, in experiments, 20% of the spirulina bioplastic was still present after 22 weeks of breakdown – as for banana skins (Iyer et al., 2023). Still, even that has to be better than the fossil-derived alternative, especially as the bioplastic breaks down without leaving microplastic behind (Rob Waugh). But, twenty-two weeks plus seems a long time for the material to break down, and isn’t the rapid disintegration the ’soundbite’ used in the Yahoo!news report’s headline here implies…

*** But, surely, a trick is being missed here? Spirulina is probably better known as a foodstuff (Orio Cifferi; Fehmida Iyer Visnagarwala) – apparently as popular with the ancient Aztecs (Nicholas DeRenzo) as NASA astronauts (Giacomo Fais et al.). Although heavily promoted as a ‘superfood’ in the late 20^th century – thanks to the efforts of its advocates and devotees such as Christopher Hills, and Robert Henrikson – it never really took off as the natural food that would save the world from starvation. However, spirulina is still important regionally as a food source (M Ahsan B Habib et al.), and is widely-promoted as a healthy food supplement (Joe Leech; Angela Haupt). So, rather than trying to make spirulina bioplastic more resistant to breakdown upon contact with water, maybe enhance that property in such a way that it can be exploited, not only as an eating utensil with non-liquid foods, but which also dissolves in hot water. That way you can use your knife, fork, etc. to eat with, and then make into a protein-rich slurry as a nutritious drink for later. That gives more marketability for the bioplastic and avoids any concerns about disposing of it in the environment. Another ‘win-win’? And, noting that Iyer et al’s organic spirulina was sourced from Nuts.com, a purveyor of a range of dietary supplements, maybe the utensils could be marketed by that company..?

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Cover: Sawdust and Chainsaw. Image: Canva.