Key Findings of the IISER Kolkata Study

Pollution Levels in Sundarbans

  • High concentrations of microplastics discovered in the Mooriganga estuary near Sagar Island
  • Microplastic levels increased by roughly 40% during monsoon season due to rainfall washing inland urban waste into the delta
  • Around half of identified plastics were fibres (from textiles), followed by fragments
  • Most common materials: Polypropylene (packaging) and PET (water bottles)

Formation of 'Plastispheres'

  • Plastics weather, crack, and break down into nanoplastics
  • These cracks host complex microbial communities called 'plastispheres'
  • Plastispheres alter marine ecological processes and accelerate carbon cycling

Threat to Blue Carbon Efficiency

  • Plastics are roughly 90% carbon, acting as artificial carbon sinks
  • They leach Dissolved Organic Carbon (DOC) into water as they degrade
  • Leached DOC acts as artificial food, enabling rapid bacterial growth beyond natural levels
  • This disrupts natural carbon cycles, rendering Sundarbans 'less blue'

Understanding Microplastics and Nanoplastics

Size Classification

  • Microplastics: Less than 5 millimetres (size of sesame seed or smaller)
  • Nanoplastics: Less than 1 micrometre (1,000 nanometres)

Origin Classification

  • Primary Microplastics: Intentionally manufactured tiny (microbeads in facial scrubs, microfibers from synthetic clothing)
  • Secondary Microplastics: Formed from breakdown of larger plastics (water bottles, fishing nets, plastic bags) due to UV radiation and weathering

Environmental Impact Mechanisms

  • Bioaccumulation and Biomagnification: Marine organisms mistake microplastics for food; they accumulate and magnify up the food chain
  • 'Trojan Horse' Effect: Plastics absorb toxic pollutants (heavy metals, POPs) and deliver concentrated doses when ingested

Sundarbans: Key Facts

Geographical Location

  • World's largest contiguous mangrove forest on delta of Ganges, Brahmaputra, and Meghna rivers
  • Flows into Bay of Bengal, spanning India (West Bengal) and Bangladesh
  • Mosaic of islands shaped by tidal waters in tropical and subtropical zones

Ecological Significance

  • 'Sundari' Tree (Heritiera fomes): Dominant species with hardwood and pneumatophores (breathing roots)
  • Blue Carbon Sink: Mangroves efficiently sequester atmospheric CO₂ in biomass and soil
  • Natural Bio-Shield: Protects coastal communities from storm surges, tsunamis, and cyclones

Conservation Status

  • Tiger Reserve: Declared in 1973 under Project Tiger
  • National Park: Upgraded in 1984
  • UNESCO World Heritage Site: 1987 (Indian portion); Bangladesh portion added in 1997
  • UNESCO Biosphere Reserve: 1989 (MAB program: 2001)
  • Ramsar Site: 2019 — largest Ramsar Site in India

Biodiversity

  • Royal Bengal Tiger: Only mangrove forest in the world inhabited by tigers
  • Estuarine Crocodile, Northern River Terrapin (critically endangered), Gangetic dolphins

Related PYQ Analysis

  • Prelims (2012): Sundarbans declared Tiger Reserve — Answer: 1, 3 and 4 (Bandipur, Manas, Sundarbans)
  • Mains (2019): Question on mangrove depletion and coastal ecology significance