Inputs of metals such as lead, nickel and chromium are being added to the river in addition to the urban flushing and surface run off into it, says a team led by scientist J Pandey from Banaras Hindu University (BHU) which conducted investigations on a 20 km stretch of the river in Varanasi, a major pilgrim site in India.
During the study spanning from 2006-08 at twelve sampling stations along a twenty kilometre long stretch of Gang's river with three sites selected at each station, the team found that mid-stream water of the river in the city was invariably contaminated by heavy metals such as cadmium, chromium, copper, nickel, lead and zinc.
"Highest concentrations of cadmium, chromium, copper, nickel and lead were recorded during winter and that of zinc during summer season. The overall concentration of heavy metals in water showed that zinc content was at a higher scale followed by nickle, chromium, lead, copper and cadmium," says the team which released the report recently.
Researchers included K Shubhashish and Richa Pandey from Centre of Advanced Study in Botany of Banaras Hindu University.
Due to heavy toxicity of heavy metals, contaminations have serious human health associated risks such as cancer and skin diseases besides memory loss.
The sites from where samples were picked were Adalpura, Bypass upstream, Bypass downstream, Samne Ghat, Ravidas Park, Assi Ghat, Dandi Ghat, Dashaswamedh Ghat, Manikarnika Ghat, Lal Ghat Laght, Raj Ghat upstream and Raj Ghat downstream.
The data indicates that although chromium and copper remained below their maximum admissible concentrations,levels of cadmium and lead in mid-stream waters at five out of six stations were higher than their respective maximum admissible concentration.
It was found that except for zinc, other metal concentrations in water were recorded highest during winter followed by summer and rainy seasons.
"There is dearth of studies explicitly addressing the heavy metal contamination of fresh water resources, linked to atmospheric deposition. The present study is an attempt to investigate the magnitude of contamination of Ganga water at Varanasi in relation to atmospheric deposition of six important heavy metals," say researchers.
The main sources of dispersion of these heavy elements into the atmosphere are urban - industrial emissions in adjoining areas. Vehicular emission is the main contributor to urban particulates, says the report.
"Re-suspension of the land - deposited particulates could further substantiate atmospheric loading and deposition of heavy metals," it adds.
Predominant, south westerly wind has further raised the atmospheric loading and transport of heavy metals towards down wind locations.
Since the stream flow restricts cross stream lateral mixing of surface-fed materials, atmospheric deposition can be considered as the major factor responsible for mid-stream heavy metal contamination of the Ganga, says the study which points out that the aerial catchment can sizeably contribute to surface water contamination of potentially toxic metals.
"This invites serious attention from human health perspective since Ganga water is also used for drinking by a large number of people particularly in northern India," says the study.
