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Pollutants such as microplastics may be causing growth defects in fish, such as skeletal deformities, in river Cauvery, finds a new Indian Institute of Science (IISc) study.
The study published in the journal Ecotoxicology and Environmental Safety was led by Upendra Nongthomba, a professor in the Department of Molecular Reproduction, Development and Genetics (MRDG), IISc Bangalore.
Nongthomba had noticed physical deformities in some fish during his trips to the backwaters of the Krishna Raja Sagara (KRS) Dam while having fried fish on the Cauvery riverbank. Soon, his lab conducted a comprehensive study of pollution at the KRS Dam and its potential effects on fish.
The IISc team collected water samples from three different locations with changing water flow speeds – fast-flowing, slow-flowing and stagnant. Water speed affects the concentration of pollutants in river water.
In the first part of the study, the team analysed the physical and chemical parameters of the water samples and found that excluding one, all parameters fell within the prescribed limits. The exception was dissolved oxygen (DO), whose levels were much lower than they needed to be in water samples from the slow-flowing and stagnant sites. Water samples also had microbes and bio-indicators of water contamination such as cyclops, daphnia, spirogyra, Spirochaeta and E. coli.
#Microplastics may be causing growth defects in fish in the Cauvery River, finds a new study by MRDG, IISc researchers. Zebrafish embryos treated with polluted water showed skeletal deformities, DNA and heart damage & other ailments. https://t.co/F5BuYkbKpK#IIScresearch pic.twitter.com/rTSRBQfOIc
— IISc Bangalore (@iiscbangalore) April 12, 2022
The IISc researchers used the Raman spectroscopy technique to detect microplastics, which are minute pieces of plastic often invisible to the naked eye, and toxic chemicals containing the cyclohexyl functional group.
Microplastics are found in several household and industrial products. Chemicals containing the cyclohexyl group, such as cyclohexyl isocyanate, are generally used in the agriculture and pharma industry.
In the second part of the study, the team investigated the impact of pollutants on wild fish and found that those fish exposed to water from the slow-flowing and stagnant sites experienced skeletal deformities, DNA damage, early cell death, and heart damage and increased mortality. These defects were seen even after microbes were filtered out, suggesting that microplastics and the cyclohexyl functional groups are responsible for the ailments in the fish.
The researchers also observed unstable molecules called ROS (Reactive Oxygen Species) in the cells of the fish that had abnormalities. The ROS build-up damages DNA and affects animals.
