BENGALURU: Pollutants like microplastics present in the Krishna Raja Sagara reservoir (Mandya district) may be causing growth defects in fish, including skeletal deformities, in the Cauvery river, according to a study by the Indian Institute of Science (IISc) on pollution in the dam and potential effects on fish.
Published in journal ‘Ecotoxicology and Environmental Safety', the study was led by Upendra Nongthomba, professor of molecular reproduction, development and genetics. "I've long cherished going to KRS backwaters and having fried fish on the banks of Cauvery," Nongthomba said, adding he has been lately noticing physical deformities in some of them which got him to wonder if water quality had something to do with it.
Nongthomba said the findings "may not be alarming yet for humans, but long-term effects can't be ruled out". The first author of the study, Abass Toba Anifowoshe, a PhD student in Nongthomba's lab, said: "When water is polluted, it is capable of causing diseases, including cancer."
For analysis, researchers collected water samples from three different locations with varying speeds of water flow — fast, slow and stagnant — since water speed is known to affect concentration of pollutants.
"In the first part of the study, Nongthomba's team analysed physical and chemical parameters of water samples. All but one of them fell within the prescribed limits. The exception was dissolved oxygen (DO), whose levels were much lower than they needed to be in samples collected from the slow-flowing and stagnant sites. Water from these sites also had microbes such as Cyclops, Daphnia, Spirogyra, Spirochaeta and E. coli, well-known bio-indicators of water contamination," an IISc statement reads.
IISc added that using the Raman spectroscopy technique, they detected microplastics and toxic chemicals containing the cyclohexyl functional group. A functional group refers to atoms in a compound that determine its chemical properties.
Microplastics — minute pieces of plastic often invisible to naked eye — are found in several household and industrial products, and chemicals containing the cyclohexyl group are commonly used in agriculture and the pharmaceutical industry.
"In the second part of the study, researchers investigated whether pollutants in water could account for developmental abnormalities seen in wild fish. They treated embryos of the well-known model organism, zebrafish with water samples collected from the three sites, and found that those exposed to water from the slow-flowing and stagnant sites experienced skeletal deformities, DNA damage, early cell death, heart damage, and increased mortality," the statement reads.
These defects, IISc said, were seen even after microbes were filtered out, suggesting that microplastics and cyclohexyl functional groups are responsible for the ailments in the fish.
Researchers also found unstable molecules called reactive oxygen species (ROS) in cells of fish that developed abnormally. ROS build-up is known to damage DNA and affect animals in ways similar to what researchers saw in fish treated with water from the slow-flowing and stagnant sites.
Other studies have shown that microplastics and chemicals with the cyclohexyl group lead to decreased DO, which triggers ROS accumulation in animals like fish, IISc added.
