Pollutants such as microplastics may be causing development problems in fish, including skeletal malformations, according to a recent study from the Indian Institute of Science (IISc). The study was headed by Upendra Nongthomba, a Professor at the IISc’s Department of Molecular Reproduction, Development, and Genetics (MRDG). It was published in the journal Ecotoxicology and Environmental Safety.

Nongthomba, who enjoys freshwater fish, became interested in their malformations and conducted a study on this aquatic species. “Over the years, I have cherished going to the backwaters of the Krishna Raja Sagara [KRS] Dam and having fried fish on the Cauvery Riverbank,” he was reported as saying. However, he recently saw physical defects in some of them and began to question if the quality of water had something to do with it.

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“Water is essential for everyone, including animals and plants. When it is polluted, it is capable of causing diseases, including cancer,” said Abass Toba Anifowoshe, a PhD student in Nongthomba’s lab and the study’s lead author.

As a result, Nongthomba’s group undertook a detailed assessment of pollution at the KRS dam and its possible consequences on fish. They took water samples from three separate locations with differing water flow speeds – fast-flowing, slow-flowing, and stationery – since water speed is known to alter contaminant concentration.

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Nongthomba’s team analysed the physical and chemical properties of the water samples in the first stage of the investigation. Except for one, they were all inside the allowed limits. The exception was dissolved oxygen (DO), which was substantially lower than it should have been in samples obtained from slow-flowing and stationary areas. Microbes such as Cyclops, Daphnia, Spirogyra, Spirochaeta, and E.coli were also found in the water from these sites, which are well-known bio-indicators of water pollution.

They discovered microplastics – minute bits of plastic that are typically undetectable to the human eye – and harmful substances containing the cyclohexyl functional group using a method known as Raman spectroscopy (a functional group refers to atoms in a compound that determine its chemical properties). Microplastics may be found in a variety of home and commercial items, and cyclohexyl-containing compounds, such as cyclohexyl isocyanate, are widely utilised in agriculture and the pharmaceutical sector.

Nongthomba’s team studied if contaminants in water may account for the developmental anomalies found in wild fish in the second portion of the study. They treated zebrafish embryos with water samples obtained from the three sites and discovered that those exposed to water from the slow-flowing and stationary sites had skeletal malformations, DNA damage, early cell death, heart damage, and higher mortality.

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These impairments were observed even after microorganisms were removed, suggesting that microplastics and cyclohexyl functional groups are to blame for the fish’s diseases. The researchers also discovered unstable chemicals known as ROS (Reactive Oxygen Species) in the cells of the improperly developing fish. The OS build-up, according to the statement, is known to harm DNA and impair animals in ways similar to what Abass and Nongthomba saw in fish treated with water from slow-flowing and stagnant areas.

Other research has found that microplastics and compounds with the cyclohexyl group reduce DO, which causes ROS buildup in animals such as fish. “The quantities we’ve recorded may not be concerning for people right now, but long-term impacts cannot be ruled out,” the researcher stated. However, he also stated that he needs to learn more about how microplastics enter the body and harm the host.