When microplastics flood rivers

Emerging scientific evidence indicates the rising threat to India’s rivers in the form of degraded bits of plastic, writes Spoorthy Raman

The Pitcairn Islands, a group of four volcanic islands, lie smack in the middle of the South Pacific Ocean, between South America and Australia. In 2019, when scientists visited Henderson Island, one of the islands with no people, they were baffled to find over four billion plastic pieces on the pristine beaches!

With plastic comprising over 80% of the ocean litter, it’s no surprise they found their way to the island, hitchhiking on the waves. But, how do plastics from land come to the oceans? It’s through all of the world’s rivers, which dump 60 billion pieces of plastic into the seas every day. In a year, that’s over two million tonnes of plastic.

India is the third biggest generator of plastic waste in the world. Global Plastic Watch puts plastic waste produced per Indian at four kilograms each year. The Ganges, the second most polluted river in the world, discharges 1,05,000 tonnes of plastic (roughly the weight of over 200 blue whales) each year into the Indian Ocean. What makes plastics a worrisome pollutant in our rivers is their tiny form, called microplastics, which are about the size of a sesame seed (0.5 mm) or less.

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Degraded from bigger chunks of plastic, like carry bags or plastic bottles, microplastics are hard to get rid of. “Once they are in the environment, they tend to stay there for several hundred years,” says environmental scientist Gopala Krishna Darbha from the Indian Institute of Science Education and Research, Kolkata.

Today, microplastics are found in every corner of the world: from the Mariana trench to Mount Everest, the Arctic to the Antarctic. It’s also found in human poop and blood.

Scientists have a fair understanding of how much microplastics are in the ocean and how they affect the health of seabirds, algae, mussels and other marine organisms. However, few studies focus on microplastics in rivers.

“India is a vast country with thousands of rivers, but there are only a handful of reports on microplastic pollution from Indian rivers,” says Anish Kumar Warrier, a microplastics researcher from the Manipal Academy of Higher Education (MAHE). Even those handfuls of reports reveal the alarming scale of this invisible pollutant.

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No river untouched

Microplastics end up in the rivers from our household and industrial sewage, leaking wastewater treatment plants, garbage dumps, agricultural and road runoffs, textile industries, cosmetics and discarded fishing gear like ropes, nets, lines and floats. Not all microplastics in the river end up in the ocean; some settle in the sediments too and accumulate over time. When river water is used for drinking and irrigation, they get into our food and body.

The scientific data collected so far indicate the microplastic presence in all rivers studied. In the lower Ganga, Darbha’s study sampled five sites, from Balia of Uttar Pradesh to Diamond Harbour of West Bengal, and found 380 to 684 microplastic pieces per million litres of water, weighing 143-340 grams. Darbha says samples from Balia and Patna, cities that are densely populated, had the highest number, and the tributaries of the river bring in more.

Another study estimated that the river discharges up to 1.3 billion microplastics into the Indian Ocean each day. In the Brahmaputra and the Indus river sediments, microplastics less than 150 microns, twice the thickness of human hair, are more abundant than bigger microplastics. In Uttar Pradesh’s Prayagraj, the confluence of Ganga and Yamuna, both rivers have comparable levels of microplastics in their sediments.

South India’s lifeline Kaveri was also found to contain upto 700 pieces of microplastics per kilogram of sediment. Chennai’s Kosasthalaiyar River had twice the concentration of microplastics compared to the Adyar River. Kerala’s Muthirapuzha River, which flows in the not-so-densely populated areas of the state also had trace levels of microplastics.

The Koshi River, which flows in the Himalayas, also contains microplastics at levels slightly lower than Chennai’s rivers. Warrier’s study, which examined microplastics in Netravati’s water, found about 288 pieces of microplastics, on average, per million litres of water.

Many shapes, forms and hazards

Based on their origins, microplastics differ in shape, colour and chemical composition. In the rivers studied, fibres originating from washing clothes and fishing gear; films from degrading carry bags and packing materials; beads from cosmetics; and fragments from packing materials dominate.

Although plastic objects come in all colours, white and transparent microplastics, degraded from coloured plastics that lose their dye over time, were prominent. Coloured microplastics primarily came from fishing gear and clothes. The colours also determine how much sunlight plastics absorb and how quickly they break down into microplastics.

The most prominent type of microplastics included polyethylene used in making grocery bags and plastic toys, polyethylene terephthalate (PET) used for bottles and packaging, polypropylene used in machinery and medical supplies, and polyvinyl chloride (PVC) used in pipes and cables. “PVC is considered the most hazardous plastic polymer,” warns Darbha, adding that it releases benzene, a cancer-causing compound, as it degrades.

These plastic polymers differ in their density. Some stay afloat and reach the oceans, while others sink to the bottom and get eaten accidentally by fish that mistake them for food. Studies have corroborated this by showing the presence of fibres and fragments in the guts of fish.

Sometimes, microplastics are laden with harmful chemicals, which make the river water toxic. In other cases, harmful bacteria may grow on them, posing a biohazard. As river water recharges groundwater, microplastics smaller than what the soil can filter, escape into groundwater.

In July, India announced a ban on single-use plastics like straws and earbuds to reduce plastic pollution. While Warrier says this is a good initiative, he is sceptical of its impact. Instead, he suggests tackling them at the source by setting up proper waste disposal and management, reducing, reusing and recycling plastic, and educating people. Darbha wants authorities to help people and factories involved in the growing plastic manufacturing industry find alternative employment. He also urges governments to promote bioplastic production and incentivise ragpickers, who are a vital part of waste collection and recycling in India.

As for you and me? We could start with generating less plastic waste, and importantly, hold our authorities accountable for action on reducing microplastic pollution in the environment, including rivers.