Syllabus:
GS3: Conservation, environmental pollution and degradation, environmental impact assessment.
Context:
A recent study published in the journal Nature revealed that microplastics are now so deeply embedded in the ocean’s structure that they are altering the planet’s biogeochemical cycles, especially the carbon cycle.
Key Findings from the Study
- Microplastics (1 and 100 micrometres) dominate the marine environment, while Larger plastic fragments (100 to 5,000 micrometres) tend to remain near the surface.
- For the first time, Scientists have analysed the Vertical Distribution of Microplastics in detail, using data from 1,885 ocean stations gathered between 2014 and 2024.
- Smaller microplastic particles have been detected as deep as 100 metres within ocean gyres (large, slow-moving ocean currents that trap debris).
- Microplastic Concentration by Depth and Location:
Impact on Ocean Carbon Cycle:
- Plastic debris adds allochthonous carbon (external carbon) to marine ecosystems.
- In subtropical gyres, microplastic carbon, which was 0.1% of total particulate organic carbon (POC) at 30 metres, increased to 5% at 2,000 metres.
- This ratio may rise further, as microbes consuming microplastics and their metabolic byproducts could disrupt processes like nitrification and denitrification.
- This proportion may grow over time, affecting carbon dating.
- A 5% plastic-C contribution could make POC samples appear ~420 years older than they are.
| Location | Depth | Microplastic Concentration (particles/m³) |
| North–South Atlantic transect | 100–270 m | 1,100 |
| North Pacific Subtropical Gyre | 2,000 m | 600 |
| Arctic Ocean | 2,500 m | 200 |
| Mariana Trench | 6,800 m | 13,500 |
Biological and Ecological Effects:
- Microplastics, along with their byproducts (metabolites, organic debris), may affect microbial processes such as nitrification and denitrification, disrupting nitrogen balance.
- Ocean gyres trap microplastics, forming large-scale plastic convergence zones.
- Plastics move up the food chain as predators eat contaminated prey, potentially affecting larger species and humans.
- Settling plastics alter seabed ecosystems and disrupt habitats for benthic organisms.
Particle Composition and Sources:
- They detected more than 56 polymer types in the dataset.
- Buoyant polymers, comprising nearly half of global plastic production dominating subsurface microplastic presence.
- Dense microplastics like Polyethylene Terephthalate (PET) were unevenly distributed in smaller size fractions, particularly in the North Pacific Subtropical Gyre, likely after extensive weathering.
- Fishing gear (nylon and polyester nets) was identified as a major source of microplastic pollution.
- The atmosphere-ocean influx of microplastics was estimated at 0.013 to 25 million tonnes annually, with polyester making up a significant portion of airborne microplastics.
About the Microplastics (less than 5 mm)
They are found in a variety of products, ranging from cosmetics and synthetic clothing to plastic bags and bottles. Many of these products easily enter the environment as waste.
Microplastics are divided into two main types: primary and secondary.
- Primary microplastics are manufactured in small sizes for specific uses. Examples include microbeads in personal care products, plastic pellets (nurdles) used in industrial manufacturing, and plastic fibers found in synthetic textiles like nylon.
- Secondary microplastics form when larger plastics break down due to environmental factors. This degradation occurs through processes such as wave action, wind abrasion, and exposure to ultraviolet (UV) radiation from sunlight.
Properties of Microplastics:
- Composed mainly of carbon and hydrogen atoms bound together in polymer chains
- Contain chemical additives such as: Phthalates, Polybrominated diphenyl ethers (PBDEs) and Tetrabromobisphenol A (TBBPA).
- These chemical additives can leach out after the plastics enter the environment.
Mains Practice Question
Q: “Microplastic pollution has emerged as a significant threat to marine ecosystems and is now disrupting key biogeochemical cycles in the ocean.” Discuss the key findings of recent research on microplastics in oceans and their implications for global climate regulation and marine biodiversity.