Tale of Two Rivers


How pollutants like microplastics and fertilisers are damaging riverine ecosystems

The Cauvery river near the Krishna Raja Sagar (KRS) dam (Photo: Abodh Kumar Jha)


It’s 2022, which means that if the word “river” crops up in a conversation among college students, it would most likely be in the context of a Buzzfeed quiz that seeks to categorise them into a type of river. With the vast number of rivers in India, such a quiz would probably offer a captivating, if misguided, thrill of self-discovery. However, unlike these algorithm-derived virtual results, something about rivers that is fast setting in stone (apart from literal riverbeds), is the decay in their quality due to rampant exploitation in order to meet the needs of our civilisation.

As rivers around the world spill over with contaminants and garbage, and their flow patterns shift due to human-induced climate change, they can spawn diseases in not only the creatures they carry but also in humans who live off of them. Two groups at IISc have been studying the effect of specific contaminants – microplastics and fertilisers – in two major rivers in peninsular India. Research around fertilisers established that human activities such as agriculture were slowly but surely changing the kind of ions present in rivers, altering the chemistry of their basins. In a related vein, a study revolving around microplastics explores the developmental defects that will only escalate as microplastics contaminating rivers collect in our bodies.


Zombie apocalypse: Zebrafish edition

Upendra Nongthomba, Professor and current Chair of the Department of Molecular Reproduction, Development and Genetics, has shared a long history with the Cauvery river. As someone who has spent more than nine years studying and living in Mysore, Nongthomba feels a deep connection to this river that flows through the area. “I still frequently visit Mysore, at least once in every 4-5 months,” he explains enthusiastically. “And I like going to the Cauvery backwaters, and eating fried fish from the area.”

It was during one of these visits that serendipity struck. He began noticing some unusual deformities in some of the fish being sold and became curious about what was causing these deformities. Although his lab has been using zebrafish as a model to study the toxic effects of contaminants for some time, it was Anifowoshe Abass Toba, a graduate student who joined his lab in 2019, who decided to spearhead a study on the impact of the Cauvery river on the fish living in it. The long-term goal of this project was to understand the effects of polluted water on human health. The discoveries that Abass made using zebrafish were as remarkable as they were disturbing.

Skeletal deformed fish collected from KRS dam (Photo: Anifowoshe Abass Toba)


Abass started his work from the ground up. The first step for him was to make arrangements to collect the water from the Cauvery. After getting ethics approval from the Cauvery Neeravari Nigama Limited, he travelled to the river frequently during the pre-monsoon period between 2019 to 2021 for water sample collection. With timely assistance from local fishermen, he could also measure the pH, temperature and concentration of dissolved oxygen immediately after collecting the water.

While researchers have reported earlier that the concentration of dissolved oxygen in the Cauvery has been affected, Abass and Nongthomba both emphasise the woeful lack of any research that seeks to unveil the presence of contaminating microbes and even more dangerously, microplastics. Microplastics have emerged as a dangerous player in the ever-expanding pollution landscape of the 21st century, as they are present in everything from microwavable containers to beer to table salt. Occupying less than 5 millimetres of space in diameter, microplastics are virtually impossible to remove even after the water has been filtered, and are detrimental to human health as well as other vegetation and animals. Alarming new research has shown that these potent contaminants have already entered our bloodstream, with babies and younger children especially susceptible to the accumulation of microplastics in their internal organs.

Scientists believe that one of the primary ways in which microplastics could influence our metabolism is by triggering the generation of a class of compounds known as Reactive Oxygen Species (ROS). ROS interact with various proteins and molecules in our body to hasten ageing, induce inflammatory reactions and cause damage to our DNA. Through a technique known as Raman spectroscopy, Abass was able to identify a variety of microplastics in the Cauvery water.


Through a technique known as Raman spectroscopy, Abass was able to identify a variety of microplastics in the Cauvery water


To study the consequences of these ROS in zebrafish, Abass treated zebrafish embryos to the river water for 96 hours. “We observed a wide range of skeletal deformities, possibly because the microplastics in the water interfere with zebrafish development,” he explains. Among these deformities are the improper curvature of the spine, bent tails, irregular larval characteristics and defects around the cardiac area. To conclusively determine if microplastics were indeed responsible for these effects, Abass also treated another set of zebrafish embryos with filtered Cauvery water, thereby removing all impurities other than microplastics. The embryos and larvae continued to show growth defects, proving that microplastics were capable of wreaking havoc during development and possibly after too. Although Abass and Nongthomba are yet to analyse the effects of microplastics on humans, they and other scientists are reasonably confident that similar dangers await us.

The research team walking towards the skipper at the KRS dam site
of the Cauvery river (Photo: Abodh Kumar Jha)


The ionic basis of pollution

For Ramananda Chakrabarti, Associate Professor at the Centre for Earth Sciences, river chemistry is a fundamental process, crucial to understanding how water interacts with the Earth. As he puts it, “In rivers, the chemistry is largely dictated by the kind of rocks that the water flows over, causing the rocks to weather. As a result, the constituents of these rocks dissolve in the water, altering its composition. This can then influence both the recent environment and the long-term atmospheric composition.” Although this might not sound very significant, it can have far-reaching consequences that only gradually become apparent.

A few years ago, Ramananda, along with Shiba Shankar Acharya, a National Postdoctoral Fellow in his lab, turned their attention to the Mahanadi river. They started looking at both the natural and human factors that dominate the chemistry of the water in this river. Shiba explains his motivation: “The Mahanadi river is interesting to study because it is one of the largest rivers in peninsular India, and has a unique riverbed consisting of carbonate rocks upstream of the Hirakud Dam, while the area farther downstream is dominated by silicate rocks.”

Valens Hishamunda, Shiba Acharya, and Rahul DasGupta (left to right)
(Photo courtesy: Ramananda Chakrabarti)


Additionally, information about the Mahanadi basin’s composition is mired in confusion. For instance, several studies have reported that the main chemical signature of the river is dominated by carbonates while others suggest that it consists of both silicates and carbonates. Some studies claim that human-induced activities have significantly altered river chemistry, while others refute it.

Piecing together the source of each ion present in the river is nothing short of chemistry-intensive detective work. “Identifying and measuring the ions and radiogenic strontium isotopes present in the river water allows us to pin down if the ion emerged from fertiliser runoff or from a particular industry,” explains Shiba.

The Mahanadi river weaves around three important urban settlements namely Sambalpur, Cuttack and Pradeep. To analyse the effect of various discharges from these areas into the river, the authors measured a pollution index. This pollution index was a ratio of contributions of sulphates, chlorides and nitrates to all the ions in the river water – ions that primarily enter the water due to civilisation-induced activities. Nitrates, in particular, have also been widely recognised as an indicator of discharge of fertiliser into the water, particularly during the monsoon and pre-monsoon season. Interestingly, the researchers found the pollution index to be relatively low when compared to other rivers, possibly because the contaminating ions rapidly migrate through the river, and are ultimately diluted by the water.

Collecting the water is a herculean task largely because it has to be sampled from various locations, further complicated by the need to transport it hundreds of kilometres for analysis. For this study, Shiba and his team collected water at different points along a distance of 500 km, spanning the upstream and downstream stretches of the river. After measuring the pH and other properties, a few drops of acid were added to preserve the dissolved ions in the water, and then the samples were processed in the lab at IISc.


Collecting the water is a herculean task largely because it has to be sampled from various locations, further complicated by the need to transport it hundreds of kilometres for analysis


By determining concentrations of dissolved ions and radioactive isotopes of strontium ions using different types of mass spectrometers, the authors studied the impact of various candidate molecules and the way they interact to modulate river ion chemistry. They found that the chief contributors to the concentration of ions were carbonate rocks from the river bed, silicate rocks in the lower basin, fertilisers and rainwater during the monsoon period. The presence of phosphate and nitrate ions in the fertilisers and their association with strontium allows them to be easily detected. Like every other natural resource on the planet, the composition of the ions is also subject to seasonal variation, and fertilisers constitute a much smaller fraction during summers and winters.

“The ionic chemistry of rivers changes over geological timescales but it is not easy to predict those changes without a grasp on current trends and composition,” explains Ramananda. These trends are also hard to establish because it is not often easy for scientists to understand how much of the variability arises because of the natural weathering of rocks and what fraction is from human contribution. As a result, it is difficult to predict if the detrimental changes are reversible.


On lives and livelihoods

“When I was [studying] at the University of Mysore, I often used to go swimming in the Cauvery river. Now, the water looks so unappealing, I am afraid to get into it,” laments Nongthomba. The local residents face even greater struggles: their livelihoods, especially those of the fishermen, are being severely impacted. Several of the local residents shared with Abass fond memories of spending their leisure time around what used to be a clean river.

The greenery and vegetation that once flanked the Cauvery are also slowly becoming a thing of the past. As more and more river water is being redirected to meet agricultural needs, and as the river banks are being encroached upon by people to meet their livelihoods and fuel economies, the river is quickly becoming a reservoir of plastic waste, food leftovers and other debris dumped by human civilisation. For the fishermen, the fear of unemployment and the question of sustenance – the struggle to sell fish of increasingly poor health – rest uncomfortably against a backdrop of lack of education and understanding. “They are worried about the Cauvery being depleted of quality water and declining in biodiversity, but they don’t understand that their practices pollute the river too, and they are unwilling to change their ways,” explains Abass.

Fishermen who help in sample collection (Photo: Abodh Kumar Jha)


Ramananda presents another slightly disconcerting perspective. “A lot depends on how we interact with our environment,” he cautions. “For instance, if we keep pumping groundwater [out] in coastal regions, the rivers would flow in to fill that space and the sea would move into previously freshwater spaces, increasing the salinity of the rivers.” While the presence of some extra salt might not sound too scary in theory, it can completely remodel the flora and fauna of rivers and the land around it in the long run.

The leaking of contaminants such as lead and other heavy metals into freshwater sources presents yet another problem with widespread ramifications. “Once they are taken up by fish and other aquatic animals, their concentration only increases with each stage in the food chain, slowly poisoning the people who consume them,” he explains.

Both Ramananda and Shiba emphasise the need to probe deeper into understanding the links that thread together river ecology and chemistry with climate change. With this in mind, they plan to continue to delve into related facets in other rivers too, like the Godavari in peninsular India. “It is important to understand the variations that occur in river chemistry naturally over time, so we can identify the signals that we intercept because of human activities,” elaborates Ramananda. He is also optimistic about the future. “Hypothetically, if no more pollutants are added to the river, the water flowing in the river would be cleaned by the following year’s monsoon or at least be significantly diluted.”



Anusha Rastogi is an Integrated PhD student in the Division of Biological Sciences and a former science writing intern at the Office of Communications, IISc

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