Science Feature

River Ganges choking with toxic plastics

Biplab Das

doi:10.1038/nindia.2021.113 Published online 24 August 2021

Polyethylene from discarded plastic bags, food-packaging films and milk bottles is increasingly gagging the Ganges river turning it into a toxic water body downstream, research shows.

A survey of the mighty river by researchers from the Indian Institute of Science Education and Research (IISER) Kolkata portrays this grim picture of plastic pollution in India1.

Single-use plastic products, difficult to recycle and decompose, persist in landfills and flow through sewers and rivers into the oceans, endangering myriad life forms. The IISER team found a large quantity of microplastics of various sizes and colours in the river. Microplastics are tiny plastic particles mostly measuring less than 5 mm.

“The most abundant type of waste plastic material found at different sites along the river banks was polyethylene,” said lead researcher Gopala Krishna Darbha.    

They also found waste plastic materials such as polystyrene and polypropylene. Polystyrene is the plastic in throw-away cutlery, plates, cups, while polypropylene comes from potato chip bags, bottle caps and single-use face masks.

The microplastics don’t just float; they also have the potential to bind to harmful pollutants and metal nanoparticles. “Plastic particles such as polyethylene can bind to persistent organic pollutants and metal-oxide nanoparticles and leach the pollutants, increasing their toxicity, mobilisation and bioavailability,” Darbha told Nature India

Globally, 10 rivers drain almost 90 per cent of plastics into the sea. Mahua Saha, from the CSIR-National Institute of Oceanography in Goa, points out that three of these rivers – Indus, Brahmaputra and Ganges – are from India.

Saha, who is not involved in this research, said such microplastic particles could carry pathogens. The plastic particles have the potential to disrupt the balance of steroid hormone levels, delay ovulation and even inhibit the secretion of gastric enzymes in various life forms, she said. 

Hotbed of plastic pollution

To assess the plastic load in the Ganges, the IISER scientists collected water samples using mesh plankton nets towed to a boat. They also gathered sediment samples scraping the surface layer at different locations along the river banks in Uttar Pradesh, Bihar and West Bengal.  

Water samples from Diamond Harbour in West Bengal showed a significantly higher abundance of microplastics when compared with Ballia in Uttar Pradesh and Bhagalpur in Bihar.

The researchers found a dominance of films in the samples, suggesting the increased use of plastic carry bags and thin plastic films for packaging. This is a reflection of the lack of waste management practices in cities along the banks of the river, they say. Further, the presence of foam and fragments showed the abundance of discarded packaging materials and the breaking of large plastic debris.  

Another recent estimate also revealed that the Ganges, with the combined flows of the Brahmaputra and Meghna rivers (GBM), releases up to 1–3 billion microplastic particles into the Bay of Bengal every day2.

“Microplastics present a clear risk to the environment. They can alter the properties of an aquatic ecosystem, leading to death of fish, birds and marine mammals,” said Subir Kumar Nag from the ICAR-Central Inland Fisheries Research Institute in Kolkata. A high content of toxic metals were found in the microplastics. These were also found in fish, Nag said.

The presence of various carcinogenic additives such as bisphenol A or phthalates in plastics was also a threat to living organisms when ingested, he pointed out.  

Apart from urban plastic wastes, the Ganges also gets plastic debris from fishing activities. In a recent study, Wildlife Institute of India in Dehradun, collaborating with researchers from the United Kingdom and Bangladesh, identified parts of fishing gear such as nets, ropes, strings and lines at different locations in the river3. The most common plastic was nylon 6, followed by polyethylene, polypropylene and polystyrene. The researchers found that these pieces of discarded fishing gear could pose a threat to Gangetic river dolphins, various species of turtles, frogs and birds.    

Threatening life

In seas, solar radiation, wind, water and microorganisms break down microplastics into smaller particles such as nanoplastics. A solitary microplastic particle could break down into billions of nanosized plastic particles. Such nanosized plastic particles become deadlier than microplastics since they are much smaller and can easily permeate through biological membranes.   

In experiments with zebrafish, which share 70 per cent of human genes, the IISER researchers found that nanoplastics could bind to metal oxide nanoparticles and exert oxidative stress and DNA damage in cells4. A separate study found that exposure to polystyrene nanoparticles shortened the life-time of Daphnia magna, a freshwater invertebrate filter feeder, by three times5.

In a recent study, Saha and her teammates detected the presence of microplastics in marine organisms such as finfish and shellfish in an estuary where the Sal river meets the Arabian Sea in Goa6. Local humans consume shellfish as seafood. “It is really alarming since ingesting such plastic particles can alter the activities of genes, which may lead to obesity, fertility problems and even cancer,” Saha warned.

The threat to marine animals and humans continues to grow as plastic particles spread to remote places such as the Galapagos archipelago where microplastics have been found in edible fish, squid and shrimps7. A recent survey of microplastics in the air, water, salt and seafood revealed that children and adults might ingest from dozens to more than 100,000 microplastic specks each day8.

Plastic production is estimated to rise by 33 billion tonnes by 2050, Darbha and his colleagues offer a ray of hope though. The team has synthesised specific clay- and carbon-based materials from agricultural waste and an iron-modified carbon-rich material that could remove plastic particles from water9,10.    

These eco-friendly materials could potentially be used as filter cartridges for providing plastic-free drinking water, said Darbha. Such plastic-removing techniques, he noted, could have a positive impact on the lives of people around the world.


References

1. Singh, N. et al. Characteristics and spatial distribution of microplastics in the lower Ganga River water and sediment. Mar. Pollut. Bull. 163, 111960 (2021)

2. Napper, I. E. et al. The abundance and characteristics of microplastics in surface water in the transboundary Ganges River. Environ. Pollut. 274, 116348 (2021)

3. Nelms, S. E. et al. Riverine plastic pollution from fisheries: Insights from the Ganges River system. Sci. Total. Environ. 756, 143305 (2021)

4. Singh, N. et al. Metal oxide nanoparticles and polycyclic aromatic hydrocarbons alter nanoplastic’s stability and toxicity to zebrafish. J. Hazard. Mater. 407, 124382 (2021)

5. Kelpsiene, E. et al.  Long-term exposure to nanoplastics reduces life-time in Daphnia magnaSci. Rep.10: 5979 (2020)

6. Saha, M. et al. Microplastics in seafood as an emerging threat to marine environment: A case study in Goa, west coast of India. Chemosphere. 270, 129359 (2021)

7. Alfaro-Nunez, A. et al. Microplastic pollution in seawater and marine organisms across the Tropical Eastern Pacific and Galápagos. Sci. Rep. 11:6424 (2021)

8. Nor. N. H. M. et al. Lifetime accumulation of microplastic in children and adults. Environ. Sci. Technol. 55, 5084-5096 (2021)

9. Tiwari, E. et al. Application of Zn/Al layered double hydroxides for the removal of nano-scale plastic debris from aqueous systems. J. Hazard. Mater. 397, 122769 (2020)

10. Singh, N. et al. Eco-friendly magnetic biochar: An effective trap for nanoplastics of varying surface functionality and size in the aqueous environment. Chem. Eng. J. 418, 129405 (2021)