ASSESSMENT OF HEAVY METAL POLLUTION IN GANGA RIVER FROM KANPUR TO PRAYAGRAJ STRETCH, INDIA

Abstract

The growing population, the discharge of untreated industrial effluents, and the improper use of pesticides in agriculture pose significant risks of heavy metal contamination in rivers. Heavy metals not only remain in river water but also bind to suspended sediments, which eventually settle as riverbed sediment. These contaminated sediments can persist in the riverbed for extended periods and may be re-suspended during periods of high-water flow, leading to recurrent contamination of the river and downstream areas. The Ganga River holds immense cultural, spiritual, and historical significance in India. The primary objective of this study is to investigate the presence of eight heavy metals Cadmium (Cd), Chromium (Cr), Copper (Cu), Iron (Fe), Manganese (Mn), Nickel (Ni), Lead (Pb) and Zinc (Zn) in the riverbed and suspended sediments of the Ganga River over a 225 km stretch. This stretch lies between the urban centers of Kanpur and Prayagraj in Uttar Pradesh, India. Riverbed sediment samples were collected in 2019 and 2021, while suspended sediment samples were gathered in 2021 and 2022 using standard sampling methods. The concentrations of these metals were determined using Atomic Absorption Spectroscopy (AAS) (Shimadzu AA-6300). The analysis of riverbed sediment from both sampling years showed a consistent decreasing order of metal presence: Fe > Mn > Cr > Zn > Ni > Pb > Cu > Cd. For suspended sediments, the metal occurrence varied between the two sampling years, following the order Fe > Mn > Zn > Cr > Pb > Ni > Cu > Cd in 2021, and Fe > Mn > Cr > Zn > Pb > Ni > Cu > Cd in 2022. Iron (Fe) was the most abundant metal, while Cadmium (Cd) was found in the lowest concentrations. The pH of collected riverbed sediment was recorded above 7 which showed mild alkaline condition. The OM (%) in 2019 in the riverbed sediment varies from 7.31 to 9.82, with a mean of 8.35 ± 0.91 whereas in 2021 OM in the riverbed sediment varies from 4.73 to 6.57, with a mean of 5.79 ± 0.60. Risk analysis was conducted using several sediment quality indices, including the geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (CF), and pollution load index (PLI). Igeo values indicated moderate contamination (0 < Igeo < 1) of Cd in riverbed sediments, while suspended sediments were moderately iii contaminated by Cr. The average EF values pointed to moderate enrichment (2 < EF < 5) of Cd in riverbed sediments, but the suspended sediments showed only mineral level enrichment with no contamination. CF values revealed moderate contamination (1 < CF < 3) of Pb and Cd in riverbed sediments, and moderate contamination of Cr in suspended sediments. The PLI indicated that all sites studied were overall unpolluted (PLI < 1), reflecting baseline pollution levels. Based on these indices, it can be concluded that riverbed sediments are moderately contaminated by Pb and Cd, while suspended sediments are moderately contaminated by Cr. The analysis of anthropogenic (Ac) and lithogenic content (Lc) in the sediments suggested that Cd and Pb in riverbed sediments originated from human activities, while suspended sediments contained anthropogenic contributions of Pb, Cr, Zn, Fe, and Mn. Correlation study among metals, pH and organic matter showed a strong correlation between Fe and most other metals, whereas Cd had the weakest correlations with other metals. Most metals showed positive correlation with pH and organic matter. When compared to the global average of other rivers, the concentrations of Cd, Pb, and Cr in the Ganga River sediments are concerning and could lead to further degradation of sediment quality if unchecked. Given the increasing anthropogenic pressures in the river basin, appropriate management strategies are crucial to limit the direct discharge of domestic and industrial wastewater into the river. Additionally, agencies like the Central Pollution Control Board (CPCB) and State Pollution Control Boards (SPCBs) must enforce strict compliance with environmental regulations for both municipal and industrial effluents to protect the Ganga River from further degradation.