Current Knowledge on Plastic Pollution: Polymer Chemistry and Biological Effects

Written By Vaishnavi Kolluru

Due to their durability and convenience, plastics have become some of the most plentiful substances on the planet. To date, it is estimated that 6.6 billion tons of plastic have accumulated in landfills or infiltrated natural environments (“More than 8.3 billion tons of plastics made,” 2017). Plastic’s characteristic resistance to degradation has allowed for its ubiquity in various ecosystems. Organisms often mistake plastics for other compounds, leading to dismal outcomes. Hermit crabs settle into plastic bottles instead of natural shells, and birds use plastic “twigs” to build their nests. In addition, microplastics are easy for organisms to accidentally consume, due to their miniscule size (Barnes et al., 2009). The chemical properties of plastics dictate their effects on the organisms that encounter them.

Chemical Properties

To understand why plastics have the effects they do, it is critical to examine their chemical properties. Plastics are synthetic hydrocarbon polymers derived from petroleum oil, and are therefore strongly hydrophobic (“Natural vs Synthetic Polymers,” n.d.). Because of their relatively uniform structure, plastics are easily customized to fit specific needs. For example, longer chain length confers strength. So does the addition of polar groups: because polar additions encourage intermolecular attractions, they increase polymer cohesion and therefore strength. Additionally, unbranched polymers tend to be stronger than branched ones due to higher packing capacity (similar to saturated fatty acids!) (“Polymers and plastics,” 2022). Because of their capability for customization, plastics have become ubiquitous in our everyday lives. 

Additionally, plastic production has a low energy requirement, thereby facilitating mass production. Although different polymerization methods exist to synthesize different plastics, the general process involves subjecting reactants to extreme pressures and temperatures corresponding with optimal activity of the chosen catalyst (Shrivastava, 2018). This process requires relatively little energy, so plastic production and consumption rates have skyrocketed.

Environmental and Health Effects

While humans have been enjoying the diverse functionalities of plastics in day-to-day life, the detrimental effects of their accumulation have significantly harmed local population health. 

Organisms ingesting microplastics, or finely weathered-down plastics, suffer from various harmful health effects. Once ingested, microplastics can wreak havoc on an organism’s bodily functions. For example, marine animals who have consumed microplastics suffer from irregular feeding behaviors & predatory techniques, excessive inflammation, physical weakness, abnormal reproductive strategies, and mortality. Ingestion of microplastics can also have effects on biomolecular processes, including (but not limited to) DNA/histone damage and faulty energy budgeting (Bajt, 2021). 

Harmful effects have also been speculated for non-marine organisms, including humans. It is hypothesized that the gut microbiome is sensitive to microplastics, highlighting the possible detrimental effects of these substances on human digestion. In addition, it is suggested that ingested microplastics have immunotoxic effects. However, adequate research has not been performed regarding the effects of plastics on human health, so we cannot yet identify at which level microplastic consumption becomes problematic for humans. We can only assert that human exposure to plastics is significant, as evidenced by the ubiquity of these compounds, and therefore has the potential to exert major effects on human health (Hirt & Body-Malapel, 2020).

The effects of compromised health from microplastic ingestion extend farther than the organismal level; if plastic pollution is rampant enough, entire ecosystems can be decimated. This is exemplified in ecosystems with multiple trophic levels, where biomagnification of ingested microplastics heavily affects the higher-ups (Vivekanand et al., 2021). 

Additionally, it has been proposed that microplastics in aquatic biomes adsorb other hydrophobic pollutants (such as pesticides) and form a layer above the water, thereby concentrating harmful substances and increasing the likelihood of joint consumption by the wildlife. In this way, microplastics not only exert toxic effects when consumed, but also may facilitate ingestion of other harmful substances (Vivekanand et al., 2021; Ašmonaitė et al., 2020). 

Because humans depend on nature for various resources, ecological damage due to plastic pollution is an urgent issue to be addressed. 

Addressing Plastic Pollution

Several measures have been taken to reduce plastic pollution. Governmental regulations limiting plastic usage have shown little promise in alleviating this issue. Preventative solutions are ineffective in the long term due to our reliance on plastics for everyday tasks. Practical solutions consider the chemical properties of plastics to develop biodegradable alternatives.

Most plastics cannot be effectively degraded into compounds that are not prone to accumulation; breakdown creates microplastics, which have their own set of harmful effects (outlined above). However, biodegradable plastics can be broken down by microbes into compostable materials. Thus, biodegradable plastics must be synthesized from monomers that are not harmful to wildlife. 

However, it has been challenging to incorporate biodegradable plastics into regular usage. Synthesis of these plastics is more expensive and the polymerization process is more complex, so mass production is not feasible. It is important to strike a balance between environmental progress and economic decline when considering a switch to biodegradable plastics. Regardless of these obstacles, we are making progress with the shift towards biodegradable plastics (Filiciotto & Rothenberg, 2021; Harding et al., 2007).

Conclusion

The widespread use of plastics has resulted in their accumulation, which has detrimental environmental effects. Efforts to address plastic pollution have been moving slowly, as many of the solutions proposed are impractical. However, there is reason for optimism, as many scientists are working on finding more sustainable alternatives to regular plastics and studying various methods of plastic degradation.

Until then, use a paper straw instead.

Here is some interesting extra reading about this topic.

References

  • 7.9: Polymers and plastics. (2022). Chemistry LibreTexts. Retrieved November 14, 2022, from https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Chem1_(Lower)/07%3A_Solids_and_Liquids/7.09%3A_Polymers_and_Plastics.

  • Ašmonaitė, G., Tivefälth, M., Westberg, E., Magnér, J., Backhaus, T., & Carney Almroth, B. (2020, January 1). Microplastics as a vector for exposure to hydrophobic organic chemicals in fish: A comparison of two polymers and silica particles spiked with three model compounds. Frontiers. Retrieved November 14, 2022, from https://www.frontiersin.org/articles/10.3389/fenvs.2020.00087/full.

  • Bajt O. (2021). From plastics to microplastics and organisms. (4), 954–966. https://doi.org/10.1002/2211-5463.13120.

  • Barnes, D. K., Galgani, F., Thompson, R. C., & Barlaz, M. (2009). Accumulation and fragmentation of plastic debris in global environments. (1526), 1985–1998. https://doi.org/10.1098/rstb.2008.0205.

  • Filiciotto, L., & Rothenberg, G. (2021). Biodegradable Plastics: Standards, Policies, and Impacts. (1), 56–72. https://doi.org/10.1002/cssc.202002044.

  • Harding, K. G., Dennis, J. S., Blottnitz, H. von, & Harrison, S. T. L. (2007, February 25). Environmental analysis of Plastic Production Processes: Comparing petroleum-based polypropylene and polyethylene with biologically-based poly-β-hydroxybutyric acid using life cycle analysis. Journal of Biotechnology. Retrieved November 14, 2022, from https://www.sciencedirect.com/science/article/pii/S0168165607001514?via%3Dihub. 

  • Hirt, N., & Body-Malapel, M. (2020). Immunotoxicity and intestinal effects of nano- and microplastics: a review of the literature. (1), 57. https://doi.org/10.1186/s12989-020-00387-7.

  • More than 8.3 billion tons of plastics made: Most has now been discarded. (2017, July 19). ScienceDaily. Retrieved November 14, 2022, from https://www.sciencedaily.com/releases/2017/07/170719140939.htm.

  • Natural vs Synthetic Polymers - Gelfand Center - Carnegie Mellon University. Retrieved November 14, 2022, from https://www.cmu.edu/gelfand/lgc-educational-media/polymers/natural-synthetic-polymers/index.html.

  • Shrivastava, A. (2018). 2 - Polymerization. In Introduction to plastics engineering.

  • Vivekanand, A. C., Mohapatra, S., & Tyagi, V. K. (2021). Microplastics in aquatic environment: Challenges and perspectives. 131151. https://doi.org/10.1016/j.chemosphere.2021.131151.

Vaishnavi Kolluru
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