Microplastics Found in Deepest Reaches of Central Indian Ocean

Recently, a team of researchers studied and quantified the presence of microplastics (MPs) in the deep-sea sediments of the Central Indian Ocean Basin (CIOB). The research team, which was led by Dineshram Ramadoss from the CSIR-National Institute of Oceanography (NIO) in Goa, India, demonstrated that at depths of 5000 meters, the CIOB contains a significant presence of MPs in one of Earth’s most remote marine environments (1). As a result, this study raises several important questions about how these pollutants are transported to such depths.

Microplastics (MPs) are plastic particles smaller than 5 millimeters, and they are pervasive in the environment because of anthropogenic activities (2). Although each MP is usually innocuous, a significant presence of MPs poses challenges to ecosystems and the organisms that live in them (2). Many coastal habitats have been studied for their MP presence, but the CIOB has remained unstudied.

Perfect sky and water of Indian Ocean | Image Credit: Pakhnyushchyy - stock.adobe.com

In this study, the research team examined the CIOB, investigating the presence of MPs in this ocean environment. As part of their study, the research team collected deep-sea core samples from three zones in the CIOB: BC20, the Pioneer Resource Zone (PRZ); and the Indian Resource Zone (IRZ) (1). The average MP concentrations varied across these sites, with the highest levels detected at BC20 (10.2 ± 6.2 MPs/g), followed by PRZ (6.4 ± 5.0 MPs/g) and IRZ (4.5 ± 0.8 MPs/g) (1). Despite being situated thousands of meters below sea level and far from land-based pollution sources, these sediments were found to be significantly contaminated, highlighting the pervasive and far-reaching nature of plastic pollution (1).

Another aspect to this study was how the team categorized the MPs. Dividing the MPs by their shape created four distinct groups: fibers, films, fragments, and beads. The researchers then investigated what type of MP was most prevalent in the CIOB. They found that fibers were the most prevalent, accounting for 54.9% of all MP particles (1). Fiber concentrations were particularly high in all three sampled locations, constituting 62.1% of MPs in BC20, 64.1% in PRZ, and 51.8% in IRZ (1). The microplastics were predominantly colored blue, black, and red. This information is important because it allowed the researchers to infer that these colors are associated with textile and fishing industry waste.

A detailed chemical analysis of the polymer composition revealed that polyacetylene was the dominant plastic type, making up 50% of all identified polymers (1). This was followed by polyvinyl alcohol (PVAL), polyvinyl chloride (PVC), epoxy resins, and even wool fibers. Notably, smaller particles (0–1 mm in size) were more commonly observed, which increases the risk of ingestion by deep-sea organisms and amplifies concerns over ecological impacts (1).

In the CIOB, microbeads and fragments were also notable contributors to MP contamination. Because microbeads are often coming from personal care products or industrial applications, the researchers deduced that these two industries were the cause for this MP contamination. Microbeads were particularly abundant in the IRZ (23.8%) and BC20 (15.6%) (1). Fragment-shaped MPs, typically resulting from the degradation of larger plastic items, were prominent in PRZ (27.2%) and BC20 (20.7%) (1).

Given the ecological importance of the deep sea and its role in global nutrient cycling and carbon storage, understanding the mechanisms behind microplastic deposition is critical. The study calls for a deeper investigation into the sources and transport pathways of MPs, whether via ocean currents, sinking particles, or other vectors (1).

The research provides a benchmark for future studies and conservation strategies. As the researchers demonstrate in their study, the central Indian Ocean is now on the growing list of marine environments affected by microplastic pollution. This is indicative of a wider, ongoing trend occurring today, and that is plastic pollution finding a way to contaminate ecosystems thought unreachable. The ocean may be deep, but that does not mean plastic pollution cannot end up there, and that is a reminder of the ongoing importance of mitigating its effects on ecosystems around the world, including the Indian Ocean (1).

References

1. Ramadoss, D.; Biju, A.; Rathore, C.; et al. The First Report on Emerged Microplastics in Deep-sea Sediment: Insights from the Central Indian Ocean Basin. Mar. Pollut. Bullet. 2025, 211, 117435. DOI: 10.1016/j.marpolbul.2024.117435
2. Wetzel, W. Quantifying Microplastics and Anthropogenic Particles in Marine and Aquatic Environments. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/quantifying-microplastics-and-anthropogenic-particles-in-marine-and-aquatic-environments (accessed 2025-05-27).