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The proliferation of plastics in the environment is continuing to increase alongside the rise in consumer demand for polymer-based products. Despite growing concerns, the development of effective solutions addressing plastic pollution remains incomplete as ecological issues generated by plastic pollution persist.
An Introduction to Polymers
A polymer refers to a chemical structure made of repeating units that can form one-, two-, or three-dimensional networks. The repeating units are often made of carbon and hydrogen and are polymerized together to form links. Although they can be found throughout nature, as they make up structures such as DNA, polymers are often used to describe artificially manufactured products used for making plastic bottles, films, cups, and fibers.
Manufactured polymers encompass a range of products. Some common products only contain carbon and hydrogen atoms including polyethylene, polypropylene, polybutylene, or polystyrene. Others have chloride attached to the all-carbon backbone, such as polyvinyl chloride (PVC), or have nitrogen atoms as repeating unit backbone, such as nylon.
Thanks to their molecular structure and integrity, polymers are typically light and strong, resistant to heat and electricity as well as most chemicals, and are often made of petroleum, making them a particularly attractive product to manufacture a range of products. However, these same characteristics make polymers extremely difficult to breakdown in natural environments.
Polymers in the Ocean: Mechanisms and Research
By 2025, plastic waste inputs into marine systems could reach 100–250 million metric tons annually. The proliferation of plastic particles is recognized as a ubiquitous component of marine debris across all oceans and one of the top 10 emerging environmental problems for marine ecosystems.
Hereby referred to as plastic pollution, the proliferation of plastics is known to negatively impact the fitness of marine organisms and disrupt the functioning of marine ecosystems. On an organismal level, plastic particles have been documented to affect physiological, behavioral, and molecular processes due to the resilience to degradation and adverse effects caused by consumption.
Within marine systems, manufactured polymers such as polyethylene (PE)-based beads require very short periods to become unstable even without being ingested, causing increased organic matter content and the creation of oxidized groups in the surrounding seawater. This was documented in a 2018 study by Portuguese researchers, who further detailed the degradation of beads over 8 weeks. The findings demonstrated the mechanisms by which the plastic pellets experienced chemical and physical impacts when exposed to seawater, in turn affecting the seawater itself.
Overall, the effects of polymer-based plastics on marine environments are increasingly well understood due to the rise in societal concern on the effects of plastic particles. These impacts were summarized in a review published in Science of the Total Environment, which further explored how scientists are approaching the study of plastic particles, and what knowledge gaps remain.
In the review, the authors demonstrated that despite an increasing abundance of studies considering the impacts of micro- (<5mm) and nanoplastic (1–100 nm) particles, there is a disproportionate number of studies considering plastic fibers and fragments, with most studies focusing on fish and crustaceans. Contrastingly, few studies considered polypropylene, polyester, and polyamide particles despite being detected commonly in the field.
Such findings were further echoed in a review of the global distribution of microplastics and their impact on the marine environment published in the Journal Nature. Although focusing essentially on microplastics, the review confirmed the imbalanced focus on few taxonomic groups and added further caveats on a geographic scale, as only 23% of countries have carried out microplastic research. Ultimately, despite its proliferation and harmful effects, our knowledge of the global spread and effects of polymer-based plastic particles remains incomplete.
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The Emerging Solutions Addressing Plastic Pollution
Many solutions have been developed to mitigate some of the impacts of polymer-based plastic pollution. From governmental policies to international bans on certain plastics, societal concern has grown rapidly in response to the proliferation of plastic waste.
One approach has been to develop degradable plastics or to degrade existing plastics in an attempt to limit the long-term persistence of waste in the environment. Using specific microbes to degrade plastic material was suggested as a potential solution. However, a review from the Open Journal of Environmental Biology concluded that there is no effective technique that can degrade plastics with efficacy due to the combined abiotic and biotic limitations on the microbial activity as well as the difficulty to produce a beneficial by-product of the degradation.
Further challenges also occur on a larger scale when addressing plastic pollution. In marine systems, The Ocean Cleanup project illustrates the potential issues when not acknowledging the complexity of plastic proliferation. The project was praised as a potentially ground-breaking innovation to collect plastic waste from the oceans, yet the lack of scientific support and evidence-based findings resulted in limited success. Despite being deployed on an extensive scale, the bycatch of species caught in plastic at the surface and the limited processing of collected items constrained the efficacy of the project.
Ultimately, the complexity of addressing plastic pollution may require a combination of approaches. The increase in attention and interest is an important benefit for scientific research, but it also requires changes in consumer behavior as well as manufacturing to prove successful.
Polymer-based plastics are now ubiquitous throughout the natural environment, as particles have been found from the Arctic to the Marianna Trench, thus requiring a long-term and evidence-based approach to addressing such a global issue.
References and Further Reading
Ajith, N., Arumugam, S., Parthasarathy, S., Manupoori, S., & Janakiraman, S. (2020) Global distribution of microplastics and its impact on marine environment—a review. Environmental Science and Pollution Research, 27(21), 25970–25986. https://doi.org/10.1007/s11356-020-09015-5
Da Costa, J. P., Nunes, A. R., Santos, P. S. M., Girão, A. V., Duarte, A. C., & Rocha-Santos, T. (2018) Degradation of polyethylene microplastics in seawater: Insights into the environmental degradation of polymers. Journal of Environmental Science and Health, Part A, 53(9), 866–875. https://doi.org/10.1080/10934529.2018.1455381
de Sá, L. C., Oliveira, M., Ribeiro, F., Rocha, T. L., & Futter, M. N. (2018) Studies of the effects of microplastics on aquatic organisms: What do we know and where should we focus our efforts in the future? Science of The Total Environment, 645, 1029–1039. https://doi.org/10.1016/j.scitotenv.2018.07.207
Duis, K., Junker, T., & Coors, A. (2021) Environmental fate and effects of water-soluble synthetic organic polymers used in cosmetic products. Environmental Sciences Europe, 33(1), 1. https://www.x-mol.com/paperRedirect/1361806546632478720
Hermabessiere, L., Dehaut, A., Paul-Pont, I., Lacroix, C., Jezequel, R., Soudant, P., & Duflos, G. (2017) Occurrence and effects of plastic additives on marine environments and organisms: A review. Chemosphere, 182, 781–793. https://doi.org/10.1016/j.chemosphere.2017.05.096
Rana, K. I. (2019) Usage of Potential Micro-organisms for Degradation of Plastics. Open Journal of Environmental Biology, 007–015. http://dx.doi.org/10.17352/ojeb.000010