Ganga water contaminated with heavy metals
May 22, 2010 1 Comment
VARANASI: The Ganga water in Varanasi is contaminated with heavy metals like cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn).
The scientists of the Centre of Advanced Study in Botany, Banaras Hindu University (BHU), led by Dr J Pandey, conducted a study to investigate the relationship between the concentrations of heavy metals in mid-stream Ganga water and their input through atmospheric deposition at Varanasi.
“We investigated the mid-stream water quality of river Ganga as influenced by aerially driven heavy metals at Varanasi,” said Pandey adding that 12 sampling stations were selected along a 20-km long stretch of the river from Adalpura to Rajghat. The water samples collected at fortnightly intervals from all the sites were analysed for cadmium, chromium, copper, nickel, lead and zinc. The data revealed that the mid-stream water of river Ganga is invariably contaminated by these heavy metals. Highest concentrations of Cd, Cr, Cu, Ni and Pb were recorded during winter and that of Zn during the summer season.
According to the study, concentrations of all the heavy metals were high in down-stream sampling stations. Correlation analysis showed that heavy metal concentration in mid-stream water had significant positive relationship with rate of atmospheric deposition at respective sites. Although the concentrations of these metals in water remained below the permissible limits of Indian standards for drinking water, levels of Cd, Ni and Pb at three stations were above the internationally recommended (WHO) maximum admissible concentrations (MAC). These observations suggest that use of such water for drinking may lead to potential health risk in long run. The study has further relevance in understanding the atmosphere-water interaction in polluted environment and for management of water bodies.
The sites from where samples were picked included Adalpura, Bypass upstream, Bypass downstream, Samne Ghat, Ravidas Park, Assi Ghat, Dandi Ghat, Dashaswamedh Ghat, Manikarnika Ghat, Lal Ghat, Raj Ghat upstream and Raj Ghat downstream. The study was conducted for two years at the selected sites from March, 2006 to February, 2008. According to Pandey, “among the heavy metals studied, atmospheric deposition was highest for Zn and lowest for Cd. Atmospheric deposition of Pb also remained high.”
The main sources of these elements into the atmosphere are urban-industrial emissions in adjoining areas. Vehicular emission is the main contributor to urban particulate. Re-suspension of the land-deposited particulate could further substantiate atmospheric loading and deposition of heavy metals. Predominant south-westerly wind has further raised the atmospheric loading and transport of heavy metals towards down wind locations.
The study showed that these inputs are in addition to the urban flushing and surface run-off being added to the river. Since streamflow 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 river Ganga. The other members of the team are K Subhashish and Richa Pandey. The study was also published in the journal of International Society for Tropical Ecology this year.