V Nilesh By Express News Service HYDERABAD: Dangerously high concentrations of toxic heavy metals have been detected on the Husssainsagar lake bed and in the water by researchers from the Indian Institute of Technology-Hyderabad, who conducted a study to understand the intensity of heavy-metal pollution in the lake and its sediments. One of the shocking findings was the extremely high concentration of cadmium on the lake bed - 50 to 300 times more than the average shale value, which is the normal expected value of the heavy metal on a lake bed. Besides, lead was found to be six times above the normal value, and zinc, five times. Such high levels of contamination have been attributed to two main factors - inflow of industrial effluents from Kukatpally Nala, which has been carrying discharge from industries located upstream for decades, and immersion of idols during festivals like Ganesh Chaturthi. These findings, published in the journal Acta Geochimica, highlight that restoration of Hussainsagar cannot just be about preventing the inflow of sewage and industrial effluents, which the government has been trying to do and failing. A major challenge would be remediating the lake bed contaminated with toxic heavy metals. Dr T Shashidhar, one of the researchers from IIT Hyderabad's civil engineering department who conducted the study, said, "Such high concentrations of heavy metals are bound to affect the aquatic life of the lake. There is also a possibility of some heavy metals seeping into the groundwater and contaminating it." He added that his team of researchers is working on remediation of lakes contaminated with heavy metals using electrokinetic remediation, which uses direct electric current to remove heavy metal particles from lake sediments. Industrial effluents and idol immersion have found to be the two main causes behind the heavy metal contamination of Hussainsagar lake bed, as well as its water. For the study, the researchers collected water and sediment samples from different five points of the lake. Two of them were sites where idols are extensively immersed during religious festivities, one was close to the Kukatpally Nala, and two others that saw regular religious practices. The concentration of heavy metals in the lake's sediments were detected above the normal values in three of the five sites -- two sites where idols are extensively immersed, and the one close to the Kukatpally nala. Analysis of concentrations of various heavy metals revealed that the highest risk stands from significant contamination with cadmium, lead, zinc, and copper, apart from arsenic, nickel and chromium. Heavy metals were detected in quantities much above the normal values, even at a depth of 40 centimeters beneath the lake bed. Impact of idol immersion Industrial effluents carried by Kukatpally nala and discharged by industrial units manufacturing batteries, ferrous and non-ferrous metals, rubber, alloy, chemical products, in its upstream areas, are responsible for introducing a majority of heavy metals into the lake. However, immersion of idols during religious festivities contributes to sustaining these metals in the water. The researchers pointed out that immersion of idols in the lake increases suspended particles in the water. These particles then trap the heavy metals from the industrial effluents and settle down, adding to the heavy metal loads of the lake bed. Also, the plaster of paris from idols also binds well with the heavy metals, forming a concentrated layer on top of the bed. In addition to the chromium coming from industrial effluents discharged from the tanning and dying industries, high levels of the heavy metal are also found in the paints used on idols that are immersed during these festivals. Contamination of lake water Apart from its bed, the lake's water is also contaminated with high concentrations of heavy metals. However, heavy metals were found to be above the permissible limits only at the site located near the Kukatpally nala. At this site, manganese, zinc, and lead were found to be 10.73, 3.255, and 8.24 times higher than standards set for surface water quality. Cadmium was found to be as much as 18 times higher than the criteria continuous concentration (CCC) by the US Environmental Protection Agency.

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