Mosses monitor polystyrene plastic pollution

Discarded plastic* is a major source of this planet’s pollution (“the action or process of making land, water, air, etc., dirty and not safe or suitable to use”), and which is worldwide – whether on land or on, and in, the ocean. Seemingly, nowhere on Earth escapes this modern menace – plastics have even been detected at the bottom of the deepest parts of the ocean.

An example of the plastic polluted coast of Japan.
An example of the plastic polluted coast of Japan. Image: Katsuhiko Saido / Wikipedia

So prevalent and widespread has human use of plastics become that their presence in the geological record has been proposed as a marker for the so-called Anthropocene (“The Age of Humans”**, the alternative name for the Holocene epoch that began about 11,700 years ago).

However, as unsightly as readily-visible-to-the-naked-eye is macroscopic plastic pollution, it’s the much smaller – often nano-sized [“1,000 times smaller than an algal cell10 – 100 nm] – micro- and nanoplastics that may be more harmful to living things, including humans. Getting a handle on how much of those problematic plastics is present – and where they are – is therefore of interest to us all. But their detection is challenging because of the size of the offending particles.

One possible way to provide such nanoplastic-pollution monitoring has been described by Fiore Capozzi et al.. In laboratory experiments, they demonstrated that, not only does the moss Sphagnum palustre [blunt-leaved bog-moss] have the ability to intercept and retain polystyrene NPs [NanoParticles], but also that the amount of entrapped NPs increased with exposure.

Importantly, dead [or, in the language of the article, ‘devitalised’] sphagnum material was better at retaining the NPs than living material – so this is also potentially a non-moss-life-threatening technique ***. That is important because it should overcome a major ecological constraint which restricts the use of living moss material to habitats where it can grow and survive – freshwaters in the case of S. palustre.

But, as useful as is monitoring, arguably bio-accumulation of the plastics – and subsequent environmentally-sensitive disposal of the plastic-polluted plant parts – is even better. We mustn’t run before we can walk, and recognize that these initial small steps are a necessary precursor to making those bigger, environment-sustaining strides ****.

* For more on plastic in society, The Plastics Historical Society web site is worth a browse.

** So prevalent has plastic become as a potential marker for the Anthropocene, it has been suggested that this particular phase of the geological epoch be termed the Plasticene. Although this term has a direct association with the plastic mouldable and malleable modelling material known as plasticine, the Anthropocene/Plasticene is anything but ‘child’s play’!

*** That is, unless – and until – this plastic pollution-preventing technique is deemed to be sufficiently successful that mass moss-culling [sphagnicide … bryocide..?] takes place to satisfy the market’s appetite for nanoplastic-trapping material.

**** As welcome as this news is my major disappointment with the study was the fact that they didn’t take the opportunity to illustrate the article with the ‘classic’ Maltese cross images of polystyrene particles in polarized light. Apparently, this is the only man-made material that produces that pattern and which can therefore be confused with starch in the light microscope

Further reading

Law, K. L. (2017). Plastics in the Marine Environment. Annual Review of Marine Science, 9(1), 205–229. https://doi.org/10.1146/annurev-marine-010816-060409

De Souza Machado, A. A., Kloas, W., Zarfl, C., Hempel, S., & Rillig, M. C. (2018). Microplastics as an emerging threat to terrestrial ecosystems. Global Change Biology, 24(4), 1405–1416. https://doi.org/10.1111/gcb.14020

Chiba, S., Saito, H., Fletcher, R., Yogi, T., Kayo, M., Miyagi, S., … Fujikura, K. (2018). Human footprint in the abyss: 30 year records of deep-sea plastic debris. Marine Policy, 96, 204–212. https://doi.org/10.1016/j.marpol.2018.03.022

Zalasiewicz, J., Waters, C. N., Ivar do Sul, J. A., Corcoran, P. L., Barnosky, A. D., Cearreta, A., … Yonan, Y. (2016). The geological cycle of plastics and their use as a stratigraphic indicator of the Anthropocene. Anthropocene, 13, 4–17. https://doi.org/10.1016/j.ancene.2016.01.002

Ogunola, O. S. (2017). Current Advances in Strategies to Mitigate the Impacts of Micro/Nano Plastics: A Review. Journal of Environmental & Analytical Toxicology, 07(03). https://doi.org/10.4172/2161-0525.1000447

Capozzi, F., Carotenuto, R., Giordano, S., & Spagnuolo, V. (2018). Evidence on the effectiveness of mosses for biomonitoring of microplastics in fresh water environment. Chemosphere, 205, 1–7. https://doi.org/10.1016/j.chemosphere.2018.04.074

Morrison, F. A., & Winter, H. H. (1989). The effect of unidirectional shear on the structure of triblock copolymers. I. Polystyrene-polybutadiene-polystyrene. Macromolecules, 22(9), 3533–3540. https://doi.org/10.1021/ma00199a006

Bertoft, E. (2017). Understanding Starch Structure: Recent Progress. Agronomy, 7(3), 56. https://doi.org/10.3390/agronomy7030056