Microplastics are plastic particles smaller than 5 mm and have become one of the most widespread pollutants in marine ecosystems. They originate from the breakdown of larger plastics or are intentionally created for products like cosmetics and textiles. These tiny particles can be found throughout the ocean, from surface waters to deep-sea trenches. Their long-lasting presence and ability to move raise critical questions about their environmental effects and potential risks to human health. This article examines the lifecycle of microplastics in the ocean, their interactions with marine life, and possible solutions to address this pressing issue.
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What are Microplastics?
Microplastics originate from two main sources: primary and secondary.
Primary microplastics
Primary microplastics are manufactured at microscopic sizes, such as microbeads in exfoliating skincare products or synthetic fibers shed from clothing during laundry cycles. These account for 15–31% of microplastics in marine environments.
Secondary microplastics
In contrast, secondary microplastics are created when larger plastic debris, such as bottles, fishing nets, and packaging, breaks down due to factors like ultraviolet (UV) radiation and wave action.1,2
How Microplastics Enter the Ocean
Rivers act as major highways for microplastics, transporting an estimated 1.15–2.41 million metric tons of plastic waste into oceans annually.
Coastal regions near urban centers or industrial zones show particularly high concentrations due to runoff from landfills, wastewater treatment plants, and stormwater systems. For example, the Ganges River in India carries approximately 3 billion microplastic particles into the Indian Ocean daily. Offshore activities like commercial fishing and shipping also contribute, with lost or discarded gear accounting for 20% of marine plastic debris.3,4,5
Once in the ocean, microplastics are distributed globally by currents, wind, and biological processes. Buoyant particles accumulate in subtropical areas like the Great Pacific Garbage Patch, which holds 1.8 trillion plastic pieces. However, even remote regions, such as the Arctic Sea ice and the Mariana Trench, are contaminated. This shows that no ecosystem is left unaffected.2,3,6
The Vertical Journey: From Surface to Seabed
Recent studies have challenged early assumptions that microplastics float indefinitely in the ocean. It has been found that these particles exhibit dynamic movement through the water column. Smaller particles (less than 100 µm) tend to disperse widely, while larger ones (greater than 100 µm) often cluster in stratified layers or sink due to biofouling, which is the process where algae, bacteria, or organic matter attach to them, increasing their density.2,6
In coastal zones, where biological productivity is high, the sinking of microplastics is accelerated. Diatoms and calcite-forming microbes colonize these particles, forming “marine snow” aggregates that rapidly descend to the seafloor.
In offshore areas, the sinking rates are slower, allowing particles to remain in mid-water layers for decades. For example, microplastic concentrations at a depth of 2,000 meters in the North Pacific can reach up to 600 particles per cubic meter. Currently, sediments are a significant sink for these microplastics, storing about 70% of them, where they can persist for centuries due to low oxygen and light levels.2,6
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This vertical transport of microplastics has profound implications. Deep-sea organisms, including filter feeders like corals and sea cucumbers, can ingest these particles, introducing toxins into marine food webs.
A recent study published in Science of The Total Environment found a staggering concentration of 13,500 particles per cubic meter at a depth of 6,800 meters in the Mariana Trench, highlighting the extensive reach of plastic pollution.6,7
What happens to microplastics in the ocean? | Ocean Wise
Video Credit: Ocean Wise/YouTube.com
Ecological Impacts: From Plankton to Predators
Research indicates that microplastics significantly hinder the photosynthesis of terrestrial plants by approximately 12% and marine algae by around 7%. These algae are essential as they form the foundation of the ocean food web.
Consequently, this reduction in photosynthetic efficiency adversely impacts the growth of staple crops like wheat, rice, and maize, as well as the production of fish and seafood.
Zooplankton that mistake particles for food experience blocked digestive tracts, decreased feeding efficiency, and stunted growth. This disruption cascades through the food web, affecting fish, seabirds, and marine mammals.8,9
Larger species are also experiencing direct consequences. Whales, for instance, ingest millions of microplastics daily during filter-feeding, with blue whales alone consuming up to 10 million particles each feeding season.
Sea turtles and seabirds face increased mortality rates due to intestinal blockages and chemical poisoning from harmful additives such as phthalates and bisphenol A (BPA). Furthermore, microplastics can carry pathogens and heavy metals, intensifying toxicity. Hydrophobic pollutants like polychlorinated biphenyls (PCBs) can adhere to plastic surfaces, amplifying contaminant concentrations significantly compared to the surrounding seawater.2,3
The biological carbon pump is a vital process where plankton capture carbon dioxide and transport it to the deep ocean. However, microplastics affect the density and sinking speed of zooplankton feces. This hinders carbon storage and disrupts this crucial climate change mitigation system.8,9
Human Health Risks: The Invisible Threat
Microplastics permeate human diets through seafood, salt, and even drinking water. A recent study published in Frontiers in Toxicology found microplastics in 98.9% of seafood samples, with individuals potentially ingesting between 78,000 to 211,000 particles each year.
Once ingested, particles smaller than 10 µm can traverse intestinal barriers, entering the bloodstream and various organs. Microplastics have been identified in human placentas, breast milk, and brain tissue, raising concerns about inflammatory responses, endocrine disruptions, and potential neurotoxicity.10,11,12
Laboratory studies have linked microplastic exposure to oxidative stress, DNA damage, and compromised immune function in human cells. While direct causation in humans is still unconfirmed, animal studies indicate significant risks; for example, mice exposed to polystyrene nanoparticles exhibited metabolic disorders and liver dysfunction. The economic impact is severe, with fisheries losing $3,300 to $33,000 annually for every ton of plastic in oceans, and potential plastic-related liabilities exceeding $100 billion by 2030.3,10,13
Mitigation Strategies: From Policy to Innovation
Addressing microplastic pollution requires global cooperation. The 2022 UN Treaty on Plastic Pollution, signed by 175 nations, aims to curb single-use plastics and improve waste management. The EU’s 2023 ban on non-degradable microplastics in cosmetics and the U.S. Microbead-Free Waters Act of 2015 target primary sources.1,10,12
Technological innovations show promise. Nanomaterials like magnetic iron oxide nanoparticles can remove 87% of microplastics from water, while enzyme-based systems break down polymers like polyethylene terephthalate (PET) into harmless compounds. Autonomous robots, such as Sichuan University’s “robot fish,” are being tested to collect microplastics in coastal zones.10
Individuals also play a role. Reducing single-use plastics, opting for natural fibers, and supporting circular economy initiatives can stem the tide of pollution. Brands such as Patagonia recycle fishing nets into clothing materials and have diverted over 1,700 metric tons of ocean plastic.14
Microplastics: A Complex Future Lies Ahead
Microplastics represent a complex, escalating threat to marine ecosystems and human societies. Their ability to persist, spread, and harm necessitates immediate action at every level, from decreasing plastic production to enhancing cleanup technologies.
Although the challenge is significant, interdisciplinary collaboration and innovative policies provide a path forward. As research progresses, it becomes increasingly clear that protecting the ocean from microplastics is an environmental duty and a moral responsibility to future generations.
References and Further Reading
- What are microplastics? (2024). NOAA's National Ocean Service. https://oceanservice.noaa.gov/facts/microplastics.html
- Yang, H., Chen, G., & Wang, J. (2021). Microplastics in the Marine Environment: Sources, Fates, Impacts and Microbial Degradation. Toxics, 9(2), 41. DOI:10.3390/toxics9020041. https://www.mdpi.com/2305-6304/9/2/41
- Plastic Pollution in The Ocean - 2025 Facts and Statistics. (2024). Recycle Track Systems. https://www.rts.com/blog/plastic-pollution-in-the-ocean-facts-and-statistics/
- Lavars, N. (2021). Ganges river carrying billions of plastic particles into ocean each day. New Atlas. https://newatlas.com/environment/ganges-river-plastic-particles-pollution/
- Prasad, G. et al. (2025). Microplastics in the rivers of Gujarat (India) to the Arabian Sea: Assessment of the sources, distribution, and associated environmental risk. Integrated Environmental Assessment and Management. DOI:10.1093/inteam/vjaf011. https://academic.oup.com/ieam/advance-article/doi/10.1093/inteam/vjaf011/7979247
- Zhao, S. et al. (2025). The distribution of subsurface microplastics in the ocean. Nature, 641(8061), 51-61. DOI:10.1038/s41586-025-08818-1. https://www.nature.com/articles/s41586-025-08818-1
- Molazadeh, M. et al. (2024). The role of turbulence in the deposition of intrinsically buoyant MPs. Science of The Total Environment, 911, 168540. DOI:10.1016/j.scitotenv.2023.168540. https://www.sciencedirect.com/science/article/pii/S0048969723071681
- Carrington, D. (2025). Microplastics hinder plant photosynthesis, study finds, threatening millions with starvation. The Guardian. https://www.theguardian.com/environment/2025/mar/10/microplastics-hinder-plant-photosynthesis-study-finds-threatening-millions-with-starvation
- Asher, C. (2023). Microplastics pose risk to ocean plankton, climate, other key Earth systems. Mongabay Environmental News. https://news.mongabay.com/2023/10/microplastics-pose-risk-to-ocean-plankton-climate-other-key-earth-systems/
- Microplastics: Are we facing a new health crisis – and what can be done about it? (2025). World Economic Forum. https://www.weforum.org/stories/2025/02/how-microplastics-get-into-the-food-chain/
- Traylor, S. D. et al. (2024). From the ocean to our kitchen table: Anthropogenic particles in the edible tissue of U.S. West Coast seafood species. Frontiers in Toxicology, 6, 1469995. DOI:10.3389/ftox.2024.1469995. https://www.frontiersin.org/journals/toxicology/articles/10.3389/ftox.2024.1469995/full
- Impacts of microplastics on health (Signal). (2025). European Environment Agency's home page. https://www.eea.europa.eu/en/european-zero-pollution-dashboards/indicators/impacts-of-microplastics-on-health-signal
- Nyadjro, E. S. et al. (2023). The NOAA NCEI marine microplastics database. Scientific Data, 10(1), 1-12. DOI:10.1038/s41597-023-02632-y. https://www.nature.com/articles/s41597-023-02632-y
- NetPlus® Recycled Fishing Nets - Patagonia. Outdoor Clothing & Gear | Patagonia UK. https://www.patagonia.com/our-footprint/netplus-recycled-fishing-nets.html
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