Enforce effluent norms strictly: Study

CHENNAI: The Cauvery , among the country’s major rivers, carries the highest levels of chemicals despite lowest discharge of water into the sea, says a government-funded Anna University study.While the annual discharge is close to 8.3 cubic kilometres, the amount of total dissolved solids (TDS) is almost 753mg per litre, nearly five times what the Ganga carries, says the study’s final report released on December 9.The high levels of chemicals in the river have contaminated groundwater in parts of Tamil Nadu and Karnataka, including at Mekadatu, Sriramasamuthiram, Kandiyur, Appakudathan, Pannavadi and Rudrapatna , making it unsuitable for irrigation and drinking. Several textile, dyeing, cement and chemical industries located along the river course discharge tonnes of harmful effluents.“The presence of major ions such as sodium and chlorine was much higher in the Cauvery, particularly near industrial areas, coast and confluence of tributaries, compared to the other rivers studied,” said L Elango, professor of geology who headed the study.High levels of sodium can cause hypertension and reproductive toxicity in humans. Researchers attribute this to (human) activities such as discharge of industrial effuents, letting out of sewage and agricultural activities along the 800km course of the river, from Thalacauvery in Karnataka’s Kodagu to Poompuhar in Tamil Nadu where it empties into the Bay of Bengal TheBureau of Indian Standards(BIS) has set500 mg per litre as the desirable limitfor TDS in drinking water, but TDS of groundwater in most the sampling locations exceeded this limit due to longer residencetime, says thestudy.The values of pH and electrical conductivity (EC) were high near the coast, particularly in Poompuhar, making the river water and groundwater there unfitfor consumption.While high pH in water can cause eye and skin irritation, higher values of EC could reduce aesthetic appearance of water and is also insensitive to infants and heart patients, say researchers referring to a 2003 World Health Organisation (WHO) report.“Magnesium Hazard (MH) values of groundwater range between 9 and 71, and for river water, it ranges from 13.20 to 74.29. MH values greater than 50 are harmful for irrigation,” Ilango added.On the positive side, the total hardness for most of the river and groundwater samples, except near Thalacauvery, was below theBIS-permitted600 mg per litre. Water salinity was high in thecoastal region as river water mixedwithsea water.The study, basedon samples collected thrice a year ( monsoon, non-monsoon and intermittent periods) from 2013 to 2016 at 25km intervals, suggested stringent enforcement of effluent discharge norms by industries and townships along the river. The river, which accountsfor about3% of thecountry’s total cultivable land, was dry for a large part of this year as the region sufferedone of the worst droughts in the past two decades. Consequently, production of rice, sugarcane (deltaic region) and coffee (upper region) were hit.