NEW DELHI: The overall chemistry of River Ganga is much cleaner than its tarnished image, at least in terms of toxic heavy metals, says a new study by IIT-Kanpur.
While most studies point towards a deterioration of water quality of the Ganga and its environmental threat, they are mostly based on easy-to-measure water quality parameters such as biochemical oxygen demand and chemical oxygen demand (BOD and COD), dissolved oxygen (DO), pH, fecal coliform, and conductivity.
A team of scientists at the Indian Institute of Technology-Kanpur has found out that the dissolved inorganic constituents like trace and toxic heavy metals of the River Ganga can be compared to the global
average river composition, and local contamination hotspots are not persistent downstream.
The researchers came to the conclusion after carrying out 3,645 river water analyses of dissolved trace elements, measured at 38 targeted locations in the Ganga Basin collected during the pre-monsoon, monsoon, and post-monsoon seasons of 2014, 2015, and 2016.
This work was supported by the Indo-US Science and Technology Forum — a bilateral organisation under the Department of Science and Technology and US Department of States — along with Union Ministry of Earth Sciences.
The study was recently published by American Geophysical Union in the journal Geochemistry, Geophysics, Geosystems. The study also shows that the reported contamination ‘hotspots’ exist, but they are much ‘localised’ and not persistent downstream.
In fact, the dissolved trace metal composition of the river water was found to be one of the highest in sites close to the glacier (above 3,000 meters), contrary to the expected industrial zones and in and around large cities, due to high physical and chemical weathering in the glacier-front.
“All existing studies are only restricted in and around effluent discharge sites, large cities, and bathing ghats to capture contamination hotspots. They do not represent the overall water chemistry and are exaggerated estimates that are significantly biased toward geographically focused areas,” said Indra Sen, assistant professor, Department of Earth Sciences, IIT-Kanpur.
The scientists are documenting the present-day background dissolved trace element concentrations of the River Ganga to assess future water quality changes in the basin. Soumita Boral, a Ph.D. student and lead author of the study, said, "Concurrent sampling of river water along with other sources such as icemelt water, snowmelt, groundwater and rainfall allowed us to quantify the natural processes that control the distribution of trace elements in river water, and in turn, allowed us to quantify the present-day background levels.”