Heavy Metals Fractionation in Ganga River Sediments ... - Springer Link

Environ Monit Assess (2007) 132:475–489 DOI 10.1007/s10661-006-9550-9

Heavy Metals Fractionation in Ganga River Sediments, India P. Purushothaman & G. J. Chakrapani

Received: 23 June 2006 / Accepted: 26 September 2006 / Published online: 13 February 2007 # Springer Science + Business Media B.V. 2007

Abstract The Ganga River is the largest river in India which, originates in the Himalayas and along with the Brahmaputra River, another Himalayan river, transports enormous amounts of sediments from the Indian sub-continent to the Bay of Bengal. Because of the important role of river sediments in the biogeochemical cycling of elements, the Ganga river sediments, collected from its origin to the down stretches, were studied in the present context, to assess the heavy metals associated with different chemical fractions of sediments. The fractionation of metals were studied in the sediments using SM&T protocol for the extraction of heavy metals and geo-accumulation index (GAI) (Muller, Schwermetalle in den sedimenten des rheins – Veranderungen seit. Umschau, 79, 778–783, 1979) and Metal Enrichment Factor (MEF) in different fractions were calculated. As with many river systems, residual fractions constitute more than 60% of total metals, except Zn, Cu and Cr. However, the reducible and organic and sulfide components also act as major sinks for metals in the down stretches of the river, which is supported by the high GAI and MEF values. The GAI values range between 4 and 5 and MEF exceed more than 20 for almost all the locations in the downstream locations indicating to the addition of metals through urban and industrial effluents, as P. Purushothaman : G. J. Chakrapani (*) Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee 247 667, India e-mail: [email protected]

compared to the low metals concentrations with less GAI and MEF in the pristine river sediments from the rivers in Himalayas. Keywords Ganga River . Sediments . Heavy metals . Metal fractionation

1 Introduction The Ganga River is one of the most utilized rivers in the world. Due to abundant availability of water throughout the year, it has played an important role in the development of Indian civilization and economy. Increased urbanization and industrialization in the basin, has resulted in polluting the river, since the river has been a preferred waste disposal site for industrial and domestic effluents. The measurements of dissolved pollutants in the water are not conclusive due to water discharge fluctuations and low residence time of the pollutants. River sediments act as both source and sink for heavy metals and are important sources for the assessment of man-made contamination in rivers (Förstner and Wittmann 1983). During the past two decades a number of studies have been reported, which dealt with heavy metals in the sediments of the Ganga River. (Ajmal et al. 1987; Ansari et al. 2000; Gaur et al. 2005; Jain 2003; Singh et al. 1997; Subramanian et al. 1987). However, most of these studies dealt with bulk sediment analysis of only a single river or an urban center. Numerous reports have highlighted the lacunae in

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predicting toxicity of heavy metals from studying total concentrations of metals in sediments (Wallman et al. 1993). In recent times, the usage of sequential extraction procedure for the fractionation of heavy metals has been carried out to determine the amount of pollutants in the sediments. Although, numerous constraints including readsorption, H+ consumption etc. have been encountered by many workers (Alain 2001; Mossop and Davidson 2003), the usage of sequential extraction procedure proved to be a good tool for pollution monitoring. In the present study, the Protocol (701), which is recommended by SM&T, has been used, since the experiments are carried out at normal room temperature, unlike in some other

Fig. 1 Geological and location map of Ganga River basin (drawn from Singh et al. 2003)

Environ Monit Assess (2007) 132:475–489

experiments. In the present study, we have determined the heavy metals concentration in different chemical fractions of bed sediments collected from the entire Ganga River and its major tributaries. 1.1 Study area The Ganga river basin is one of the most densely populated river basins of the world and, as of 1983 census, sustains 200 millions in India, 12 million in Nepal and 30 million populations in Bangladesh. With a mean annual flow of 5.9×1011 m3 year−1 and sediment load of 1,600×1012 g year−1, the Ganga river ranks among the top 10 rivers in the world in


terms of water and sediment discharge to the world’s oceans (as in Chakrapani and Subramanian 1995). The Ganga River and many of its tributaries chiefly drain from the Himalayas and the rivers Son and Gomati drain from Vindhyans in Madhya Pradesh and swampy area in the Northern Uttar Pradesh of India, respectively. The rivers Yamuna, Alaknanda, Bhagirathi drain from the Gangotri Glacier, flow initially over Gangotri Granite and drain over the complex lithology of Himalayan terrain composed of igneous, sedimentary and the metamorphic rocks. The rocks in the drainage basin of Ganga and Yamuna consist of high grade metamorphic rocks, such as gneisses, migmatites and the unmetamorphosed rocks, dolomites, limestone and the Siwaliks of Mio-Pliocene age, which are composed of sand stone, clay and conglomerates (Fig. 1). The other Himalayan Rivers, Gandak and Ghaghara have similar lithology of metamorphic, sedimentary rocks on their drainage basin. The rivers Gomati drains from a swampy area in northern Uttar Pradesh and the river Son from the medium to high grade metamorphic rocks of Vindhyan group. These rivers drain a large portion in the Ganga plain, which consist of alluvium (Pleistocene to Holocene), derived chiefly from the rivers of Himalayas and Indian craton. Several large and small scale industries, ranging from jute, leather, cement to petrochemicals, are in operation in the Ganga river basin (Fig. 2). Fig. 2 Metal based and other related industries in the basin (from CPCB, Environmental Atlas of India 2001)

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2 Materials and Methods 2.1 Sample collection Field studies were carried out during the month of February 2005. Freshly deposited fine-grained surface sediment samples were collected from the top 5–10 cm of the riverbed. These samples were taken either in the middle or near the margins of the river’s active channel. Twenty-two sampling stations were selected from the whole stretch of the river as shown in Fig. 1. Four samples from the River Yamuna at the locations namely, Delhi, Agra, Hamirpur, Allahabad were taken, respectively. One sample each from the major tributaries the Gomati, the Ghagra, the Gandak, and the Son at the locations Lucknow, in and around Patna, respectively were also collected. One sample from the distributary Bhagirathi (local name) at Azimghanj (West Bengal) was taken, which represents the farthest sample from the origin of the river. 2.2 Sample analysis The sequential extraction of the heavy metals was carried out using the SMT standard protocol (EUR19775-BCR 701) (Rauret et al. 2001; Table 1). The reagents used for each extraction step is briefly mentioned in Table 1. The extracted fractions and

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Table 1 SM&T sequential extraction method (Rauret et al. 2001) Fraction

Extraction method

Extracted sediment components

F1, Acid soluble F2, Reducible F3, Oxidisible

0.11 M HOAc, 16 h 0.5 M NH2OHHCl, pH 2 (HNO3), 16 h 30% H2O2, pH 2 (HNO3), 2 h at 85°C, extracted with 1 M NH4OAc pH 2 (HNO3), 16 h Hot HNO3 conc.

Exchangeable ions and Carbonates Iron–Manganese oxides Sulphides/organics

F4, Residual

the digested sediments were analyzed for Cr, Mn, Fe, Co, Ni, Cu, Zn, and Pb by Perkin–Elmer ICP-MS at Institute Instrumentation Centre, IIT Roorkee. Certified SGR1 for the fractions and MAG1 for the total metal concentration and residuals were used as standard for evaluating the precision and accuracy of the above analytical procedure. The standards were rerun after measurement of five samples. The standards varied in concentration from the actual values by a maximum of 6–10% of the certified values. Extreme care was taken to avoid external contamination, by using chemicals of supra-pure grade and ultra pure water. The geo-accumulation index (GAI) proposed by Muller (1979), was used to compare accumulation of each metal in the chemical fractions. Geo-accumulation index was calculated as, Igeo=log2 [Cn /(1.5× Bn)], Where Cn =measured concentration; Bn =back ground value (Average Shale value); 1.5 = back ground matrix correlation factor. The gradational sequence of metal accumulation is numerical values ranging from 0 to 6, 6 represents very strong pollution intensity, 3 represents moderate pollution and 0 is unpolluted. The Metal Enrichment Factor (EMF) in each chemical fraction was calculated by taking the ratio between the metal concentrations in the sample at a particular location in comparison to the concentration in the sediment at the origin of the river (B1 in Fig. 1). Similar procedure has been used earlier by Audry et al. (2004) for calculation of GAI in bulk sediment compositions.

Metals bound in lithogenic minerals

(Table 2). Iron concentrations range from 80,412 mg kg−1 at Gangotri (B1) in the upstream site, to 231,244 mg kg−1 at Son (T4) in the downstream location and are the dominant metal followed by manganese. Iron and manganese make up the bulk (90%) of the composition. All other metals have concentrations of few hundreds mg kg−1 with the urban and industrialized areas showing higher concentration; Cu=5,214 mg kg−1 at Agra (Y2); Pb= 603 mg kg−1, Cr=5,167 mg kg−1at Delhi (Y1). These values are higher compared to the earlier reports of Singh et al. (2003) and Ansari et al. (2000). Davidson et al. (1998) argued that, because of the extreme recovery of metals during fractionation, the sum total may far exceed the pseudo-total composition. The GAI values in the metals at different locations are highly variable. The metal Fe shows unpolluted to moderately polluted nature in the upstream region, whereas it falls under the high pollution category in the downstream sediments. Similar behavior is observed for the other metals too, indicating to the river sediments getting increasingly polluted downstream, may be from anthropogenic additions. Lead pollution is very high from sediments collected in urban areas (Delhi (Y1), Agra (Y2)) and show extreme GAI values, may have been caused by large scale vehicular traffic in the region, catering to tourism. 3.2 Metals in different fractions 3.2.1 Fraction 1: Exchangeable and carbonate fraction

3 Results and Discussion 3.1 Total metal concentration The total metal concentration was calculated by summing up the concentration from all the fractions

Iron is the dominant element, representing up to 90% of metals associated with exchangeable and carbonate fraction. Manganese is also present in appreciable concentrations. The variations in Fe and Mn concentrations in different samples are large, which indicate


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Table 2 Concentration of heavy metals at different locations (sum of all fractions) (Mg kg−1) (GAI values are given in parentheses) Location

Fe

Mn

Co

Cu

Zn

Pb

Ni

Alaknanda @ Vishnu Prayag Srinagar Bhagirathi @ Gangotri Uttarkashi Ganga 2 Rishikesh Brijghat Farukkabad Kanpur Allahabad Varanasi Patna Bhagalpur Farakka Yamuna@ Delhi Agra Hamirpur Allahabad Gomati@ Lucknow Ghagra@ Patna Gandak@ Patna Son@ Patna Bhagirathi @ Azimghanj

95,467 (1) 177,390 (2) 80,412 (1) 136,324 (1) 123,055 (1) 137,150 (1) 66,550 (0) 128,595 (1) 171,296 (2) 197,315 (2) 173,066 (2) 192,105 (2) 145,039 (2) 122,286 (4) 141,923 (4) 156,227 (4) 171,740 (4) 210,712 (4) 178,486 (4) 177,354 (4) 231,244 (5) 146,724 (3)

6,779 (3) 12,442 (4) 2,982 (2) 5,297 (3) 9,514 (3) 9,684 (3) 5,841 (3) 7,956 (3) 11,484 (4) 13,884 (4) 11,861 (4) 24,365 (5) 6,336 (3) 10,487 (1) 10,376 (2) 11,566 (2) 15,126 (2) 14,979 (2) 12,838 (2) 12,699 (2) 22,520 (2) 9,755 (1)

176 (3) 458 (5) 259 (4) 294 (4) 235 (4) 425 (4) 113 (3) 225 (3) 284 (4) 419 (4) 322 (4) 461 (5) 230 (4) 249 (4) 256 (4) 296 (4) 295 (4) 365 (4) 293 (4) 230 (4) 624 (5) 246 (4)

574 (4) 1,004 (4) 416 (3) 488 (3) 439 (3) 310 (3) 364 (3) 607 (4) 418 (3) 528 (3) 348 (3) 532 (3) 415 (3) 579 (4) 5,214 (6) 460 (3) 380 (3) 760 (4) 357 (3) 336 (3) 926 (4) 321 (3)

624 (3) 447 (2) 295 (2) 376 (2) 301 (2) 346 (2) 359 (2) 878 (3) 438 (2) 433 (2) 396 (2) 394 (2) 423 (2) 847 (3) 2,759 (5) 371 (2) 445 (2) 834 (3) 406 (2) 363 (2) 458 (2) 345 (2)

449 (4) 1,297 (6) 614 (5) 420 (4) 653 (5) 211 (3) 179 (3) 427 (4) 363 (4) 387 (4) 345 (4) 344 (4) 190 (3) 603 (5) 1,034 (6) 389 (4) 339 (4) 570 (5) 373 (4) 332 (4) 326 (4) 414 (4)

129 219 155 209 151 166 122 195 269 394 254 270 343 216 272 259 215 374 250 213 487 215

the variable nature of sediments. In general, the midstream locations show high Fe concentrations. The tributary Gandak (T4) also has very high Fe associated with the exchangeable fraction. Zinc is dominant, in the urbanized locations of mid-stream and close to mega-cities such as Delhi (Y1) and Kanpur (G3). The metals present in the exchangeable and carbonate fractions are considered to be weakly bound and may equilibrate with the aqueous phase, thus becoming more bioavailable (Baruah et al. 1996). Metals in this fraction are the most mobile and readily available for biological uptake in the environment. Presence of Mn, Zn and Cu in higher concentration indicates their ability to replace Ca in carbonate minerals due to their similar ionic radii and charge.

Cr (1) (2) (1) (2) (1) (1) (1) (1) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (2) (3) (2)

507 (2) 530 (2) 497 (2) 545 (3) 594 (3) 509 (2) 208 (1) 251 (1) 240 (1) 334 (2) 317 (2) 356 (2) 4,875 (6) 5,167 (6) 836 (3) 496 (2) 579 (3) 588 (3) 246 (1) 254 (1) 223 (1) 477 (2)

river and in samples collected from all urbanized cities including, Delhi (Y1), Agra (Y2), Kanpur (G3), Lucknow(T1). Industrial discharge may be one of the factors, for the increased metal concentrations. There is a sharp divide in metal concentrations between upstream (low concentrations) and downstream (high) samples. The Fe and Mn hydroxide constitutes a significant sink for heavy metals in the aquatic system. This phase accumulates metals from the aqueous system by the mechanism of adsorption and coprecipitation (Bordas and Bourg 2001). The relatively higher concentrations of elements such as Cu, Zn, Cr, Ni, etc., associated with this fraction are caused by the adsorption of these metals by the Fe–Mn colloids.

3.2.2 Fraction 2: Fe–Mn hydroxides

3.2.3 Fraction 3: Associated with sulfides and organics

The metals which have been associated with Fe–Mn hydroxides fractions, show increased Fe concentrations and decreased Mn concentrations as compared to Fe and Mn associated with exchangeable and carbonate fraction. The metals Cu, Zn and Cr show appreciable concentrations in the mid-stream of the

The metals associated with sulfides and organic matter show very less abundance. Fe associated with this fraction is higher in the upstream samples as compared to the downstream samples. Because of the high flow and abundant oxygenated condition, the metals have already been released into the water

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Fig. 3 Concentration (%) of iron at different locations

system. The affinity of heavy metals for organic substances and their decomposition products are of great importance for the release of the metals into water. Organic matter, with high molecular weight acids, plays an important role in the distribution and dispersion of heavy metals, by mechanisms of chelation and cation exchange processes. The oxide fraction is important for all metals, with the exception Fig. 4 GAI and MEF values for iron in the Ganga River

of Mn, and dominant for the metals Cu, Cr, Fe, Zn and Pb (Dollar et al. 2001). 3.2.4 Fraction 4: Associated with residuals Higher amounts of Fe and Mn are observed in the residual fractions of sediments. The residual fractions represent samples, which have been leached off


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Fig. 5 Concentration (in percent) of manganese at different locations

of other metals to various other fractions. Since, Fe and Mn make up considerable proportion of rocks and sediments, the residual fractions show higher Fe and Mn concentrations. Similarly, the metals associated with crystal structures also, are not released easily by mild acids. However, when the samples are digested completely with strong acids, all the metals get into the dissolved forms. Hence, under normal sediment–water interaction, there is Fig. 6 GAI and MEF values for manganese in the Ganga River

not much possibility for the release of these metals. Because of the effective dissolution, the residual fraction shows high Cu, Co, Pb, Zn, Ni and Cr concentrations. The residual or lithogenic fraction is a major carrier of transition metals in most aquatic systems. The concentration of heavy metals in the crystalline fraction is largely controlled by the mineralogy and the extent of weathering. Heavy metals in this form are not soluble under experimental

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Fig. 7 Concentration (in percent) of cobalt at different locations

conditions and hence may be considered to be held within the mineral matrix. 3.2.5.1 Iron and manganese A comparison of the distribution of iron in different fractions shows, residual fraction to contain high Fe content. The percent abundance of the element is very uniform at all locations (Fig. 3). More than 80% Fe is present in the residual fraction. Iron is associated with sulfides and organics, which is higher in the upstream and subsequently, get reduced along downstream. There is no large variation in abundance of Fe in Fe-Mn hydroxides and exchangeable and carbonate fraction.

Fig. 8 Concentration (in percent) of nickel at different locations

The high concentration of Fe in the oxidisable fraction upstream may be due to the presence of disseminated pyrites in the sedimentary sequences. The Fe-Mn hydroxide fraction, generally considered as the scavenging form of metals, shows high concentration in the urban and industrial areas. The reducible fraction shows high GAI (4–5); with maximum values at Ganga in Bhagalpur (G7) and Gomati (T1) in Lucknow, in the downstream locations, whereas the upstream locations (A1, B1) (Fig. 4) show no accumulation. MEF also shows very little or no enrichment in the upstream, but as the river


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Fig. 9 Concentration (in percent) of chromium at different locations

reaches the plains, the ratio increases in the reducible fraction (>40 at Ganga in Bhagalpur (G7), >20 at Yamuna (Y1) in Delhi), indicating an anthropogenic input into the system. Iron is a major component of the sewage sludge. The increase of Fe in the residual fraction suggests considerable conversion of the amorphous Fe oxides into more stable, residual crystalline Fe oxides (Staelens et al. 2000). Similar to Fe, residual fractions have high Mn contents, as compared to the other fractions (Fig. 5). Residual fractions make up >70% of the total Mn Fig. 10 GAI and MEF values for cobalt in the Ganga River

contents. Exchangeable and carbonate fraction as well as, organic fraction is also a major sink for Mn. Manganese shows preferable association with the carbonates due to its bivalent Mn2+ nature (Lindsay 1979; Staelens et al. 2000). The GAI and EMF values are high in the downstream locations in the exchangeable and carbonate fractions and Fe–Mn hydroxide fractions (Fig. 6). The mid-stream samples show high Mn concentrations in the oxidisable fractions. The river is a dynamic system and prevalence of high redox conditions are not encountered,

484


Fig. 11 GAI and MEF values for nickel in the Ganga River

however in the mid-stream locations, discharge of sewage and industrial sludge into the river, may have increased the Mn contents. The GAI value in the oxidisable fraction is contrary to that of the concentration in this fraction. It shows an unpolluted to moderately polluted nature. The available and reducible fractions are the dominant fractions with GAI of 4 at Bhagalpur (G7) and Son (T4) in Patna. MEF values also show high ratios in the downstream with the values going upto 63 at Son (T4) in Patna, 15 at Ganga in Bhagalpur (G7) in the reducible fraction Fig. 12 GAI and MEF values for chromium in the Ganga River

and 14 at Ganga in Bhagalpur in the available fraction. This shows that, carbonate, exchangeable and reducible fractions act as high mobilisers of Mn. 3.2.5.2 Cobalt, nickel and chromium Cobalt, nickel and chromium are present in very low concentrations. In the upstream location, significant amounts of Co are present in the oxidisable fraction constituting up to 70% at Gangotri (B1) (Fig. 7), whereas, in the midstream higher Co is detected in the FeMn hydroxide and oxidisable fractions. After residual fraction,


485

Fig. 13 Concentration (%) of copper at different locations

oxidisable and FeMn hydroxide fraction seems to be the major sink for Co. Ni in general shows a diversified nature (Fig. 8) in its distribution. The oxidisable fraction dominates in the upstream (70% in Gangotri, B1) and the reducible fraction, with percentage around in 50% for almost all locations. In general, Ni is present predominantly in oxidisable and residual fractions in aquatic sediments (Staelens et al. 2000; Zhai et al. 2003). Cr shows higher concentrations (Fig. 9) in the oxidisable fraction throughout the stretch, a very little

Fig. 14 Concentration (%) of zinc at different locations

amount of Cr is present in the carbonate fraction, with a maximum of 2.5%, may be due to absence of its carbonate fraction in the natural environment (Förstner and Wittmann 1983). The GAI and EMF values in different fractions of these elements are shown in Figs. 10, 11 and 12 for Co, Ni, and Cr, respectively. Irrespective of the variations in concentration in different fractions, the concentrations indicate unpolluted to moderately polluted nature in all fractions except the reducible fraction. The GAI value in the reducible fraction is

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Fig. 15 Concentration (%) of lead at different locations

high at Son (T4) in Patna (6) for Co and 5 at (G7) Bhagalpur. The MEF value behaves similar to that for the Co and Ni, but the metal Cr shows minor variation in its MEF value throughout the stretch, except in urban areas and in tributaries, where it shows high value in residual fraction. The locations Farakka (G8) and Delhi (Y1) show a high value in the reducible fraction. Domestic wastes are the major source for Co in aquatic environments (Zhai et al. 2003), whereas, nickel wood, fuel combustion, agricultural wastes and domestic sludge are the major source for anthropoFig. 16 GAI and MEF values for copper in the Ganga River

genic Ni. Ni and Cr accumulations are higher in urban centers, and also in towns with leather, carpet and steel foundries. 3.2.5.3 Copper, lead and zinc In nature, Cu, Pb and Zn prefer association with sulfides, as these elements are chalcophile in character (Krauskopf and Bird 1995). However, the oxide and carbonate compounds act as scavenging fractions for these metals, as is evident from the high concentrations in the downstream locations. In the present study, Cu is mostly associated with oxidisable fraction (80% in Gangotri, B1), followed


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Fig. 17 GAI and MEF values for zinc in the Ganga River

by reducible fractions (52% at Bhagalpur, G7) (Fig. 13). Zhai et al. (2003), have reported a strong affinity between Cu and organic matter, due to the high complexing tendency of Cu for organic matter. The release of copper from the oxidisable to reducible phase occurs due to the release of organic bound Cu, caused by the decomposition of easily degradable organic matter into more soluble organic chelates and the microbial activity which enhances the precipitation of hydrous oxides of Mn and Fe Fig. 18 GAI and MEF values for lead in the Ganga River

(Staelens et al. 2000). Anthropogenic Cu is also introduced into the river from the numerous metal alloy, electrical, and electronic industries, present along the river course in the mid-stream region. Zinc shows high concentrations in exchangeable and carbonate fractions in the upstream (60% Srinagar, A2) and later in the downstream gets concentrated in the Fe– Mn hydroxide (43% in Son, T4, at Patna) and oxidisable (57% in Yamuna, Y1, at Agra) fraction (Fig. 14). Fe– Mn phase acts as good scavengers for Zn (Irabien and

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Velasco 1999; Prusty et al. 1994; Staelens et al. 2000). The pH of water plays an important role in the sorption of Zn from water to sediment. At alkaline pH, the sorption on to sediment surface is very effective. It is also one of the major by products in almost all types of industrial and domestic wastes. Unlike Cu and Zn, lead shows higher values in the residual phase (>70%). This is due to its less bio available nature. Fe–Mn hydroxides are also an important sink in many samples. In reducible conditions, Pb forms strong bonds with sulfides, but this is rarely found in riverine condition, high concentrations of lead in the upstream sediment may be due to the presence of lead as lead sulfides. The reducible and carbonate fraction acts as a mobile fraction for the Pb (Gambrell et al. 1991). The reducible fraction has the highest values next to the residual phase, with highest value at (Y2) Agra (52.4) and the minimum value of 0.22 at Srinagar (A2). The low value at the upstream of the Alaknanda and Bhagirathi and the higher values at the downstream and the rivers in the plain shows the significant anthropogenic source (Fig. 15). In the upstream locations, lead pollution is very less (GAI=0), whereas the downstream locations show high pollution index. Similar to the high total Pb concentrations at Delhi (Y1) and Agra (Y2), lead accumulation index at Delhi and Agra is estimated to be 6, which is due to the heavy vehicular traffic pollution. Fe–Mn hydroxide fraction in the mid-stream and downstream locations also shows appreciable lead contents. This can be attributed to specific sorption of Pb on to Fe oxides. The GAI and MEF (Figs. 16, 17 and 18) values show similarity in these elements. The MEF values are higher in the reducible fractions, >365 in Yamuna (Y2) at Agra, 43 in Ganga (G7) at Bhagalpur for Cu, 18 and 53 in Yamuna at Agra for Zn and Pb, respectively. These values strengthen the statement that the Fe–Mn oxy hydroxides act as main scavenging materials for many heavy metals.

4 Conclusions The sediments in the Ganga River basin are derived from varied lithology and environmental conditions. The river flows through differing geologic, topographic, hydrologic and industrial regions and the river sediments reflect the influence of the natural and


man-made additions. The increased association of high metal contents in the reducible fractions, after residual phase, in general indicates significant anthropogenic additions. The application of the GAI and MEF in the fractions helped us to understand the metal accumulations in sediments and the enrichment of metals downstream due to additions from industrial and domestic effluents. In the upstream, the concentration of metals in general is low and typically shows low GAI (0–1). The metals show high concentration in the residual fraction except Cu, Cr and Zn, which occur mostly in the oxidisable fraction. The downstream locations show high concentrations of metals in the reducible fraction (>50%). The GAI and MEF values are also high for all the metals in this fraction, indicating the river encounters high pollution in the downstream region, due to discharge of particle laden industrial and urban effluents. Similarly, the largest tributary Yamuna contains sediments with high metal contents along downstream. Big In locations close to cities, such as, Delhi (Y1), Agra (Y2), Lucknow (T1) show high concentrations of metals in the reducible fraction and show very high GAI value 5–6 for all the metals along with extremely high MEF values. A good correlation is observed between GAI and MEF in most of the locations for most of the metals, showing the appropriateness of such comparisons in sediment quality studies. Acknowledgements We deeply appreciate and acknowledge the funds made available for the present study by a research project grant to GJC, from the Ministry of Human Resources Development (MHRD), Government of India.

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