By Emily Kaloudis
It is safe to assume that people generally know that pollution and littering are bad. The majority of humankind try not to throw their plastic bags into rivers, and many locations around the globe are creating policies against even selling such single-use plastics. These are great advancements our population has made in recent years, but unfortunately macroplastics (things you can see with your naked eyes- such as a plastic bag or spork) are not the only problematic pollutant plaguing our oceans. In fact, visible trash only makes up 1% of plastic litter world wide, the rest is unaccounted for (Amaral-Zettler, 2020). Microplastics are particles of plastic that are smaller than five millimeters in diameter. These tiny particles are not something most organisms can see, but they are still composed of the toxic materials that make plastic.
Marine animals suffer this issue particularly harshly. Filter feeders, in particular, take in huge quantities of water to filter out plankton or other microorganisms that they feed on, and they will unknowingly concentrate large quantities of microplastics in their digestive tract, which their bodies can not process. One study by Valente et al. tracked three elasmobranch species, also known as cartilaginous fishes such as sharks and rays, in the Tyrrhenian Sea off the western coast of Italy (2019). The study found that none of the three shark-like species could process or expel microplastics from their intestines, despite having evolved drastically distinct diets and digestive processes.
Another concerning facet of microplastics is what is living on them. In marine environments certain life sustaining nutrients such as Nitrogen, Iron, and Phosphorus are sparse, but plastic happens to be a great source of these elements. Microorganisms attach themselves to the free floating plastic particles and colonize it rapidly. These populations that have made their home on plastic are referred to as the plastisphere. Researchers such as Amaral-Zettler et al. are studying whether the populations living on plastics differ than populations living on organic surfaces (2020). One hypothesis is that once settled, a microorganism is unlikely to give up its spot to become free floating again. Biofilm formers in particular prefer an attached lifestyle, and these organisms produce problematic microbial biofilms that can include harmful pathogens and algae.
Further still, some scientists wonder if microorganisms could be used to treat our planet’s plastic problem (Valente, 2019). Certain microorganisms break down the plastic while they colonize it, utilizing the aforementioned elemental nutrients buried inside. While this sounds like a perfect solution, the reality is that as the organisms break down the plastic, they biotransform it into dangerous compounds which are then released into the water and directly affect human and animal food sources. Despite these grim findings, the scientific community is making great strides in studying the effects of microplastics, which until recently were largely unknown. Modern technology is also making it possible to lower mass consumption of plastic products by replacing it with multi-use items which can help alleviate the pressure that plastic litter is placing on the ecosystem. Purchasing reusable products and buying in bulk are just a few ways to assist in the ongoing battle against plastic litter.
Amaral-Zettler, L.A., Zettler, E.R. & Mincer, T.J. Ecology of the plastisphere. Nat Rev Microbiol (2020). https://doi.org/10.1038/s41579-019-0308-0
Valente, T., Sbrana, A., Scacco, U., Jacomini, C., Bianchi, J., Palazzo, L. Exploring microplastic ingestion by three deep-water elasmobranch species: A case study from the Tyrrhenian Sea. Environmental Pollution. (2019). https://doi.org/10.1016/j.envpol.2019.07.001