Air – Borne Heavy Metal Contamination to River Ganga (India)

摘要

A two year study was undertaken at Ganges basin of India to evaluate theatmospheric input of six heavy metals to river Ganga. Atmospheric bulk deposition wascollected on a fortnightly basis at 8 river sites from April 2006 through March 2008 todetermine atmospheric loading of heavy metals to river Ganga. The sampling protocolconsisted of bulk collectors placed at 24 locations (3 at each site) selected along a 20 kmlong tract of river Ganga at Varanasi, India. The atmospheric fluxes of six heavy metalsto river Ganga were estimated as (g ha~(-1) y~(-1)) : Cd – 0.56 – 20.15; Cr – 0.34 – 8.87; Cu –1.63 – 58.17; Ni – 0.21 – 7.32; Pb – 1.80 – 124.00; Zn – 124.15 – 477.18. Atmosphericdeposition of all the elements was lowest at Adalpura (site 1) and highest at Rajghatdownstream site (site 8) receiving maximum down – wind urban industrial emissions.Zinc alone contributed to more than 68 % of total measured heavy metal input. Forseason, the atmospheric fluxes were measured highest during winter followed by summerand rainy seasons. Data on heavy metal concentrations in mid – stream water showedsignificant correlation with their respective values received through atmosphericdeposition. Corresponding to the atmospheric deposition, except for Zn, highestconcentrations of Cd, Cr, Cu, Ni and Pb in mid – stream were recorded during winterfollowed by summer and rainy seasons. Concentrations were recorded highest for Znfollowed by Ni, Cr, Pb, Cu and Cd. Concentrations of all the heavy metals were high indown – stream sampling locations. Although the concentrations of Cr, Cu and Znremained well below their maximum admissible concentrations (MAC), more than 80 %of water samples of 7 out of 8 locations sampled, showed Cd, Ni and Pb levels abovetheir respective MAC. Heavy metal loading to mid – stream implicates the adjoiningurban agglomeration of Varanasi as the principal emission source area. The atmosphericloading to the river will continue to rise with the completion of Ganga Express highway.This may lead to serious health implications in long – run since Ganga water is also usedfor drinking purpose by a large population.