River Noyyal, its tributary polluted with heavy metals, says study

‘Level of lead significantly high in water samples lifted from both rivers’

October 09, 2020 12:12 am | Updated 06:34 am IST - COIMBATORE

Alkalinity in River Noyyal is more than the permissible level for drinking water fixed by the Bureau of Indian Standards.

Alkalinity in River Noyyal is more than the permissible level for drinking water fixed by the Bureau of Indian Standards.

River Noyyal, the lifeline of Coimbatore district, and its tributary, the Chinnar, are polluted with heavy metals, says a recent study.

Samples of water, sediment and specimens of a freshwater crab species collected from the river had high presence of heavy metals such as copper, cadmium, lead and zinc, the study says.

Though similar samples from the Chinnar river showed the presence of these heavy metals, the levels were, however, not as high as those found in the samples from the Noyyal.

Samples of water and sediments from Noyyal were collected at Marudurai village in Tiruppur district and from Chinnar at Sadivayal village in Coimbatore district. Crabs were lifted with the help of farmers from two other locations. The study titled “Assessment of Heavy Metals Pollution in Noyyal and Chinnar Rivers, Western Ghats of Tamil Nadu, India with Reference to Crabs ( Gecarcinucidae )-A Baseline Study”, and authored by V. Gayathri, T. Muralisankar, R. Rajaram, M. Muniasamy and P. Santhanam, was recently published in the Bulletin of Environmental Contamination and Toxicology.

According to the researchers, the study on the pollution in the Noyyal is essential because it is a tributary of River Cauvery, the main source of water for drinking, agricultural and farming in many districts of the State.

Noyyal, which originates from the Vellingiri Hills in Coimbatore district, flows through four districts - Coimbatore, Tiruppur, Erode and Karur. The study found that the total hardness, chloride, fluoride, nitrate, residual (free) chlorine, dissolved oxygen, and alkalinity were significantly higher in Noyyal water when compared with the samples from the Chinnar. Further, pH, total hardness, chloride, nitrates, and alkalinity levels in the Noyyal water exceeded the permissible limits of the Bureau of Indian Standards (BIS 2012) for drinking water.

Zinc, cadmium and lead levels were found to have exceeded in the water samples of both rivers compared to the permissible limits of BIS and the United States Environmental Protection Agency (USEPA 2002), said the study. The level of lead was significantly high in the water samples of both rivers.

Presence of lead found in Chinnar water beyond the permissible limits of BSI and USEPA suggests that the river water was polluted by the metal, might be due to the dumping of domestic waste and agricultural activities in the river basin. The analysis of sediment samples from both rivers found a significant increase in the level of cadmium, copper, lead and zinc in Noyyal sediments compared to sediments from its tributary. Zinc content was high in the sediments of both the rivers, the study showed. It was found that the level of bio-accumulation of the heavy metals and biochemical constituents were higher in specimens of Spiralothelphusa hydrodroma crab species collected from the Noyyal than Barytelphusa cunicularis crab species collected from Chinnar.

According to the researchers, the two freshwater crabs were chosen for analysis as crustaceans-like crabs and shrimps are highly sensitive to heavy metal pollution. They tend to accumulate more heavy metals than fishes because they live in the benthic zone where the metals are stored in sediments, the study said.

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