Beyond the shoreline: Why fighting Mumbai’s microplastics starts upstream
Agapejerin, Wikimedia Commons
Mumbai’s mangroves are among the city’s most important natural protections. They help reduce coastal flooding and erosion, provide habitats for fish and birds, and store carbon. However, their roots and sediments are also trapping an invisible pollutant: microplastics.
Waste entering the sea through drains, sewage networks, roads and coastal activities is accumulating in these ecosystems. A scientific study has found thousands of microplastic particles in every kilogram of sediment sampled from six mangrove regions in Mumbai. The findings highlight how the city’s waste management practices affect its coastal environment.
The research paper , titled Assessment of secondary microplastics trapped in mangrove ecosystem of a highly populated tropical megacity, India, examined sediment samples from Gorai, Versova, Bandstand, Sewri, Vikhroli and Elephanta Island.
Researchers identified 2,035 microplastic particles, with an average concentration of 6,730.2 particles per kilogram of dry sediment. Versova recorded the highest average concentration, at 7,885.7 particles per kilogram, while Sewri had the lowest, at 5,785.7 particles per kilogram.
The researchers examined the particles based on their size, shape, colour, depth and polymer composition. They collected surface sediment from the upper five centimetres, along with samples from depths of 5 to 10 centimetres and 10 to 15 centimetres.
Silt accounted for about 78 per cent of the sediment. Fine particles, organic matter and dense mangrove roots create conditions that allow plastic particles to accumulate. The mangroves are therefore acting as sinks for pollution, retaining material that might otherwise move into the wider coastal ecosystem.
Microplastic concentrations were highest in the upper five centimetres of sediment, at approximately 7,500 particles per kilogram. At a depth of 10 to 15 centimetres, the concentration fell to about 4,380 particles per kilogram. This difference suggests that newer pollution is accumulating closer to the surface.
Regular sampling before and after the monsoon could help authorities track changes in these concentrations and identify whether pollution levels are rising or falling.
Fibres were the most common type of microplastic, accounting for 56.1 per cent of the particles. Fragments made up 38.5 per cent, while pellets and beads accounted for only 0.1 per cent.
The large proportion of fibres points towards wastewater and synthetic textiles as possible sources. Clothes made from polyester, nylon and other artificial materials release tiny fibres during washing. These can enter household drains and sewage networks, and conventional treatment systems may not remove all of them before wastewater is discharged into creeks and coastal waters.
Fragments, meanwhile, form when larger plastic objects such as bags, packaging, containers and fishing equipment break down. Exposure to sunlight, abrasion, waves and tidal movement gradually reduces these objects into smaller pieces.
Particles smaller than 100 micrometres formed the largest size category. Overall, particles below one millimetre accounted for 82 per cent of the sample. Their small size makes them difficult to remove through conventional cleanup operations and increases the possibility of ingestion by organisms living on or within the sediment.
Translucent particles accounted for 30.8 per cent of the sample, followed by black particles at 29.3 per cent. Some fish, birds and invertebrates may mistake coloured particles for food. This is a particular concern in Sewri, where mudflats support migratory flamingos and other wildlife.
However, the paper does not establish that flamingos, fish or humans are being harmed by these particles. It identifies a possible route of exposure, but further research is needed to understand ingestion, toxicity and the movement of microplastics through the food chain. The findings point to the need for prevention and further investigation, rather than conclusions about seafood safety or human health.
To identify the composition of the particles, researchers used Nile Red staining, fluorescence microscopy and Raman spectroscopy. Polyethylene was the most common polymer, accounting for 36.91 per cent, followed by polyester at 21.33 per cent and polyamide at 13.47 per cent. Polystyrene, polyethylene terephthalate and polypropylene were also detected.
The different polymers reflect the range of possible sources. Polyethylene is commonly used in bags, packaging and films. Polyester and polyamide are widely used in clothing, while polyethylene terephthalate is found in bottles and other packaging.
The findings suggest that Mumbai’s microplastic pollution cannot be addressed through a single ban or shoreline cleanup programme. It requires action across the urban systems through which plastic enters the environment.
The study also found a positive association between microplastic abundance and the presence of clay and total organic carbon. This suggests that clay-rich sediments containing more organic matter may retain greater quantities of microplastics. Future monitoring should therefore record sediment composition alongside particle counts to help explain differences between locations.
The researchers used laboratory methods including density separation, hydrogen peroxide digestion, microscopy, spectroscopy and contamination controls. However, the study covered a limited period, examined sediments only up to a depth of 15 centimetres and did not directly assess biological effects. Seasonal studies and deeper sediment sampling could provide a more complete understanding of the extent of contamination.
The findings point to the need for a regular monitoring programme across Mumbai’s mangrove regions. Sampling should cover different seasons, particularly the periods before and after the monsoon. Publishing the results in a common database would help authorities compare locations and track changes over time.
Wastewater management is another priority. Treatment plants should be assessed for their ability to remove fine plastic particles and synthetic fibres. Where feasible, tertiary filtration could be introduced. Textile manufacturers could also be encouraged to reduce fibre shedding, while filters for washing machines could help limit the release of fibres from households.
Plastic waste must also be intercepted before it reaches creeks and mangroves. Drainage channels need well-maintained screens, booms and litter traps that can withstand monsoon flows. Their effectiveness should be measured by the quantity and type of waste collected, rather than simply by the installation of equipment.
Industries and producers also have a role to play. Packaging companies should contribute to collection and recovery systems, while facilities handling plastic pellets need strict containment measures. Businesses involved in fishing, shipping and shoreline activities should establish systems to collect and return damaged nets, ropes and other plastic equipment.
Clean-up operations must be carried out carefully. Removing visible plastic waste is useful, but extensive excavation can damage mangrove roots, disturb wildlife and release buried contaminants. Preventing plastic from entering these ecosystems is safer and more effective than repeatedly removing it after it has accumulated.
Mumbai’s mangroves protect the city while retaining the effects of its waste disposal practices. The study by Selvam Kesavan and colleagues shows that plastic pollution is not limited to bottles, bags and packaging discarded along the shoreline. It also accumulates in the sediment as thousands of microscopic particles.
The findings underline that microplastic pollution is not only a conservation concern. It is also a wastewater management, infrastructure and production issue. Addressing it requires consistent monitoring, better treatment of wastewater, effective waste interception and greater accountability from industries and producers.
Protecting Mumbai’s mangroves will depend on reducing the flow of plastic into the coastal environment. The roots and sediments may continue to trap pollution, but they cannot replace the need to prevent it at source.