Nuclear Science in Action: Uncovering the Journey of Microplastics Through Ecosystems
Plastic pollution, particularly in marine environments, has emerged as one of the most pressing environmental crises of the 21st century. Of particular concern are microplastics (MPs), which are tiny plastic particles less than 5 mm in size. These particles have been found in virtually every marine habitat, from the surface of the ocean to the deepest trenches, posing severe risks to marine life (Arthur & Baker, 2012; Koelmans et al., 2019). Microplastics not only obstruct marine organisms’ gastrointestinal tracts but also act as carriers for hazardous chemicals such as plasticizers and flame retardants (Galloway et al., 2017; Sharma & Chatterjee, 2017). As a result, understanding how microplastics move through ecosystems is crucial for addressing their broader ecological impacts.
To combat the growing threat of plastic pollution, the International Atomic Energy Agency (IAEA) launched NUTEC Plastics — an initiative to address this global challenge using nuclear science and technology. NUTEC Plastics focuses on two main fronts: improving recycling technologies and tracking microplastics in marine environments. One of its core goals is to empower more than 50 laboratories worldwide with the technology and expertise needed to sample and analyze marine microplastics. These labs will also contribute to reporting on the United Nations’ Sustainable Development Goal (SDG) 14: Life Below Water, which aims to protect oceans and marine resources. This article will explore the latter, focusing on how Stable Isotope Analysis (SIA) and related techniques allow scientists to trace microplastics as they move through food webs (International Atomic Energy Agency, 2022).
Tracking Microplastics Using Stable Isotope Analysis (SIA)
Stable Isotope Analysis (SIA) has long been used to study nutrient cycles and reconstruct food webs by analyzing the ratios of isotopes, mainly carbon (δ¹³C) and nitrogen (δ¹⁵N), in biological samples. In the context of microplastic tracking, stable isotopes of nitrogen (δ¹⁵N) provide insight into the trophic position of organisms. Since the δ¹⁵N of a consumer is typically enriched by 3–4‰ relative to its diet, it allows scientists to determine where in the food chain the organism is positioned. On the other hand, carbon isotopes (δ¹³C) change very little as carbon moves through food webs, making δ¹³C an effective tool for tracking carbon sources, including plastic-derived carbon, ingested by different species. These isotopes are usually quantified by using Isotope-Ratio Mass Spectrometry (IRMS) (Post, 2002). This method provides time-integrated data on the resources organisms consume, making it particularly useful for tracking microplastics as they move through marine ecosystems (Valente et al., 2023).
Stable Isotope Techniques in Action: Case Studies
Stable Isotope Analysis (SIA), particularly Stable Carbon Isotope Labeling (¹³CLE), has been pivotal in recent studies that track the movement of microplastics through food webs. This technique involves labeling microplastic particles with the stable isotope ¹³C, allowing researchers to monitor the flow of plastic-derived carbon through different organisms. One notable study used ¹³CLE to trace polyethylene microplastics (PE-MP), which were heavily enriched with 99% ¹³C2 and sized less than 20 µm. These labeled microplastics were followed as they moved through microbial and planktonic food webs. Researchers observed that microplastic-derived carbon was incorporated into essential biomolecules, such as fatty acids, in organisms like zooplankton (Taipale et al., 2019). This finding suggests that despite low rates of direct mineralization, microplastics are being integrated into the marine food chain in nutritionally significant ways.
In another study conducted in the Garonne River, Stable Isotope Analysis was employed to explore how microplastics contaminate freshwater species. By analyzing the ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes, researchers quantified microplastic contamination in macroinvertebrates and fish. Their findings revealed that the characteristics of ingested microplastics (such as shape, color, size, and polymer composition) varied significantly between different species and environments — whether in surface waters, sediments, or within organisms themselves (Garcia et al., 2021). Interestingly, the study also found that larger organisms tended to ingest more microplastics, but there was no evidence of significant bioaccumulation across trophic levels. This indicates that most ingestion occurs through direct consumption, likely by accident rather than intentional feeding.
Further research has explored the relationship between trophic position and microplastic ingestion in marine ecosystems. One investigation applied SIA to analyze pelagic fish species from the Tyrrhenian Sea, categorizing ingested microplastics by shape, size, and color. While this study showed no apparent connection between trophic position and the amount of microplastic ingestion, it revealed that different species tend to ingest distinct types of microplastics depending on their foraging behaviors (Valente et al., 2023). These differences highlight the species-specific selection mechanisms that influence microplastic ingestion, underlining the complexity of interactions between marine organisms and plastic particles in the wild.
Applying Stable Isotope Techniques — whether in marine or freshwater ecosystems — has expanded our understanding of how microplastics are transferred between organisms. By tracking the movement of plastic-derived carbon and nitrogen through food webs, these studies provide critical data on the pathways through which microplastics are consumed, revealing the hidden ways in which plastic pollution affects marine and freshwater biodiversity.
In Conclusion…
The application of Stable Isotope Analysis (SIA) has revolutionized the tracking of microplastics through ecosystems, providing invaluable insights into their movement across food webs and their impact on marine and freshwater biodiversity. As nuclear science continues to play a pivotal role in environmental monitoring, the NUTEC Plastics initiative exemplifies how innovative technologies and global cooperation can address the growing threat of plastic pollution. By equipping laboratories worldwide with cutting-edge tools like Isotope-Ratio Mass Spectrometry (IRMS), NUTEC Plastics is advancing research and supporting efforts to achieve Sustainable Development Goals (SDGs) related to ocean health. These scientific breakthroughs are crucial for informing effective strategies to reduce plastic contamination, protect marine life, and ensure a sustainable future.
References
Arthur, C., & Baker, J. (2012). Proceedings of the Second Research Workshop on Microplastic Marine Debris.
Galloway, T. S., Cole, M., & Lewis, C. (2017). Interactions of microplastic debris throughout the marine ecosystem. In Nature Ecology and Evolution (Vol. 1, Issue 5). Nature Publishing Group. https://doi.org/10.1038/s41559-017-0116
Garcia, F., De Carvalho, A. R., Riem-Galliano, L., Tudesque, L., Albignac, M., Ter Halle, A., & Cucherousset, J. (2021). Stable Isotope Insights into Microplastic Contamination within Freshwater Food Webs. Environmental Science and Technology, 55(2), 1024–1035. https://doi.org/10.1021/acs.est.0c06221
International Atomic Energy Agency. (2022). NUTEC Plastics. https://www.iaea.org/services/key-programmes/nutec-plastics
Koelmans, A. A., Mohamed Nor, N. H., Hermsen, E., Kooi, M., Mintenig, S. M., & De France, J. (2019). Microplastics in freshwaters and drinking water: Critical review and assessment of data quality. In Water Research (Vol. 155, pp. 410–422). Elsevier Ltd. https://doi.org/10.1016/j.watres.2019.02.054
Post, D. M. (2002). Using Stable Isotopes to Estimate Trophic Position: Models, Methods and Assumptions. In Source: Ecology (Vol. 83, Issue 3). http://www.jstor.orgURL:http://www.jstor.org/stable/3071875http://www.jstor.org/stable/3071875?seq=1&cid=pdf-reference#references_tab_contents
Sharma, S., & Chatterjee, S. (2017). Microplastic pollution, a threat to marine ecosystem and human health: a short review. Environmental Science and Pollution Research, 24(27), 21530–21547. https://doi.org/10.1007/s11356-017-9910-8
Taipale, S. J., Peltomaa, E., Kukkonen, J. V. K., Kainz, M. J., Kautonen, P., & Tiirola, M. (2019). Tracing the fate of microplastic carbon in the aquatic food web by compound-specific isotope analysis. Scientific Reports, 9(1). https://doi.org/10.1038/s41598-019-55990-2
Valente, T., Costantini, M. L., Careddu, G., Berto, D., Piermarini, R., Rampazzo, F., Sbrana, A., Silvestri, C., Ventura, D., & Matiddi, M. (2023). Tracing the route: Using stable isotope analysis to understand microplastic pathways through the pelagic-neritic food web of the Tyrrhenian Sea (Western Mediterranean). Science of the Total Environment, 885. https://doi.org/10.1016/j.scitotenv.2023.163875
