Bangalore: A new study by the Indian Institute of Science (IISc) has revealed that pollutants such as microplastics in the Cauvery River can cause growth defects in fish, including skeletal deformities. Published in the journal Ecotoxicology and Environmental Safety, the study was led by Professor Upendra Nongthomba, from the Department of Molecular Breeding, Evolution and Genetics (MRDG) at IISc. Nongthomba, an avid fan of freshwater fish, noticed deformities in them and conducted a research on this aquatic species.

Over the years, I have played Krishna Raja Sagar. [केआरएस] Have enjoyed visiting the backwaters of the dam and eating fried fish on the banks of river Kaveri, he was quoted as saying in a press release. But in recent days, he noticed physical deformities in some of them and began to wonder whether the water quality could have anything to do with it, the statement read. Water is essential for everyone, including animals and plants. When it is polluted, it is capable of causing diseases, including cancer, said Abas Toba Enifowoshe, PhD student in Nongthomba’s lab and first author of the study.

Therefore, Nongthomba’s laboratory undertook a comprehensive study of pollution in the KRS Dam and its potential effects on fish. They collected water samples from three different locations, with varying speeds of water flow as fast-flowing, slow-flowing and steady as the movement of water is known to affect the concentration of pollutants. In the first part of the study, Nongthomba’s team analyzed the physical and chemical parameters of the water samples. All except one of them fall within the prescribed limit.

The exception was dissolved oxygen (DO), the level of which was much lower than that occurring in samples collected from slow-flowing and stationary sites. The waters of these sites also contained microbes such as Cyclops, Daphnia, Spirogyra, Spirochaeta and E.coli, which were well-known bio-indicators of water contamination. Using a technique called Raman spectroscopy, they detected microplastics—small pieces of plastic that are often invisible to the naked eye and that toxic chemicals contain the cyclohexyl functional group (a functional group refers to the atoms in a compound that determines its chemical properties). Microplastics are found in many household and industrial products, and chemicals containing the cyclohexyl group, such as cyclohexyl isocyanate, are commonly used in the agriculture and pharmaceutical industries.

In the second part of the study, Nongthomba’s team investigated whether pollutants in the water could be responsible for the developmental abnormalities seen in wild fish. They treated embryos of the well-known model organism, the zebrafish, with water samples collected from three sites, and found that those exposed to water from the slow-flowing and stationary sites showed skeletal deformities, DNA damage, early cell death, and fibrosis. Experienced death, heart damage. , and increased mortality. These defects were observed even after filtering the microbes, suggesting that microplastics and cyclohexyl functional groups are responsible for diseases in fish.

The researchers also found unstable molecules called ROS (reactive oxygen species) in abnormally developed fish cells. According to the statement, Os build-up is known to damage DNA and affect animals in the same way that Abas and Nongthomba observed in fish treated with water from slow-flowing and stagnant sites . Other studies have shown that microplastics and chemicals with a cyclohexyl group reduce DO, which in turn triggers ROS accumulation in animals such as fish. The researchers said that the concentrations we reported are not yet dangerous to humans, but long-term effects cannot be ruled out. However, he also said they needed to understand how microplastics actually enter and affect the host.