Sundarbans Under Microplastics Threat

• 21 Apr 2026

Source: TH  

Why in News?  

A study by Indian Institute of Science Education and Research (IISER), Kolkata, highlights that microplastics are disrupting the food web and altering the carbon cycle in the Sundarbans, raising concerns over the stability of this crucial blue-carbon ecosystem.

What are the Key Findings of the Study on Sundarbans? 

• Alarming Pollution Levels: The study uncovered high concentrations of microplastics in the Mooriganga estuary (near Sagar Island). 
  • Microplastic levels surged by roughly 40% during the monsoon season. Heavy rainfall washes inland urban waste, "colourless fragments," and older weathered plastics down the rivers and drains straight into the delta. 
• Sources:  Around half of the identified plastics were fibres (likely from textiles), followed by fragments.  
  • The most common materials were polypropylene (used in packaging) and polyethylene terephthalate (PET) (used in water bottles). 
• Formation of 'Plastispheres': High-resolution imaging showed the plastics were weathering, cracking, and breaking down into nanoplastics.  
  • These cracks host complex communities of bacteria and microbes, collectively known as 'plastispheres.' 
• Carbon Reservoir: Because these plastics are roughly 90% carbon, they are acting as artificial carbon sinks. As they degrade, they leach Dissolved Organic Carbon (DOC) into the water. 
  • The leached DOC acts as an artificial food source, enabling marine bacteria to grow and multiply rapidly beyond natural levels, leading to altered microbial dynamics and accelerated carbon cycling. 
    • While microbes on microplastics further contribute by producing biogenic carbon, intensifying disruptions in the natural carbon cycle.  
• Threat to 'Blue Carbon' Efficiency: Mangroves are vital "blue-carbon" ecosystems, normally highly efficient at capturing and storing atmospheric CO₂.  
  • The researchers warn that the artificial introduction of carbon from plastics and the resulting microbial bloom could disrupt natural carbon cycles, rendering the Sundarbans less efficient as a carbon sink (effectively making them "less blue").

Microplastics and Nanoplastics 

• Definitions and Scale: The primary difference between the two lies in their microscopic size: 
  • Microplastics: Defined as plastic fragments, fibres, or granules that are less than 5 millimetres (5 mm) in length. They are about the size of a sesame seed or smaller. 
  • Nanoplastics: These are the extremely minute breakdown products of microplastics, typically defined as measuring less than 1 micrometre (1 μm or 1,000 nanometres). 
• Classification: Based on their origin, these tiny plastics are categorized into two groups: 
  • Primary Microplastics: These are intentionally manufactured to be tiny for commercial use.  
    • Examples include microbeads used in facial scrubs and toothpaste, and microfibers shed from synthetic clothing (like polyester and nylon) during washing. 
  • Secondary Microplastics: These are formed from the breakdown of larger plastic items (like water bottles, fishing nets, and plastic bags) due to environmental weathering.  
    • Exposure to UV radiation from the sun, ocean waves, and temperature fluctuations causes the plastic to become brittle and shatter. 
• Environmental Impact: 
  • Bioaccumulation and Biomagnification: Microplastics are frequently mistaken for food by marine life, from tiny zooplankton to large whales.  
    • Once ingested, they block digestive tracts or alter feeding behaviour; these plastics accumulate and magnify up the food chain. 
  • The "Trojan Horse" Effect: Plastics act like chemical sponges. They absorb and concentrate toxic pollutants from the surrounding water, such as heavy metals and Persistent Organic Pollutants (POPs).  
    • When an animal eats the plastic, it also ingests a concentrated dose of these toxins. 

What are the Key Facts About Sundarbans? 

• Geographical Location: The Sundarbans hosts the largest contiguous mangrove forest in the world, located on the delta of the Ganges, Brahmaputra, and Meghna rivers flowing into the Bay of Bengal. 
  • It is a unique mangrove ecosystem that lies between land and sea, consisting of a mosaic of islands constantly shaped by tidal waters, and is spread across India  (within the state of West Bengal) and Bangladesh in tropical and subtropical zones. 
• Ecological Significance: 
  • 'Sundari' Tree: The forest gets its name from the Sundari tree (Heritiera fomes), a dominant mangrove species in the region known for its hard wood and pneumatophores (specialized breathing roots that grow upwards out of the mud). 
  • Blue Carbon Sink: Mangroves are highly efficient at sequestering atmospheric carbon dioxide, storing it in their biomass and underlying soil. 
    • This makes the Sundarbans a critical "blue carbon" ecosystem in the fight against climate change. 
  • Natural Shield: The dense mangrove network acts as a crucial natural bio-shield, protecting coastal communities in West Bengal and Bangladesh from the devastating impacts of storm surges, tsunamis, and cyclones that frequently originate in the Bay of Bengal. 
• Biodiversity & Wildlife: 
  • The Royal Bengal Tiger: The Sundarbans is the only mangrove forest in the world inhabited by tigers.  
  • Rich Fauna: The ecosystem supports a vast array of wildlife, including the Estuarine (Saltwater) Crocodile, the critically endangered Northern River Terrapin (Batagur baska), and Gangetic dolphins. 
• Conservation & Global Status: The Indian side of the Sundarbans holds multiple overlapping conservation tags: 
  • Tiger Reserve: Declared a Tiger Reserve in 1973 under Project Tiger. 
  • National Park: Upgraded to a National Park in 1984. 
  • UNESCO World Heritage Site: The Sundarbans National Park was designated a World Heritage Site in 1987 (the Bangladesh portion was added in 1997). 
  • Biosphere Reserve: Designated as a Biosphere Reserve by the Indian government in 1989 and recognized under UNESCO's Man and the Biosphere (MAB) program in 2001. 
  • Ramsar Site: The Indian Sundarbans was declared a Wetland of International Importance under the Ramsar Convention in 2019, making it the largest Ramsar Site in India. 

Frequently Asked Questions (FAQs). 

1. What are ‘blue-carbon ecosystems’? 
Ecosystems like mangroves, seagrasses, and salt marshes that efficiently capture and store atmospheric CO₂. 

2. What are plastispheres? 
Microbial communities that form on microplastic surfaces, altering marine ecological processes. 

3. Why are microplastics harmful to the Sundarbans? 
They act as artificial carbon sources, disrupt food webs, and reduce carbon sequestration efficiency. 

4. What is the significance of the Sundarbans? 
It is the world’s largest mangrove forest, a UNESCO World Heritage Site, and a key climate buffer. 

5. How do microplastics affect the carbon cycle? 
They release Dissolved Organic Carbon (DOC) and promote biogenic carbon production, altering natural carbon dynamics. 

UPSC Civil Services Examination, Previous Year Question (PYQ)  

Prelims: 

Q. Consider the following protected areas: (2012)

1. Bandipur  
2. Bhitarkanika  
3. Manas  
4. Sundarbans  

Which of the above are declared Tiger Reserves?

(a) 1 and 2 only  

(b) 1, 3 and 4 only  

(c) 2, 3 and 4 only  

(d) 1, 2, 3 and 4

Ans: (b)

Mains: 

Q. Discuss the causes of depletion of mangroves and explain their importance in maintaining coastal ecology. (2019)