The study area, located between latitudes 22˚13'14"N and 23˚27'00"N; longitudes 85˚11'00"E and 86˚42'50"E, consisted of three districts namely Ranchi, Saraikela Kharswan and Purba Singhbhum of the Jharkhand state, India. Subarnarekha river flows through these three districts before entering the Indian state of West Bengal near Gopiballabhpur in the West Medinipore district (Figure 1). The river during its course passes Ranchi uplands, Bhagmundi hills (Ayodhya pahar), Dalma and Dhanjori ranges. Its bed belongs to the hard rock of the Pre- Cambrian or Archaean formations comprising mainly quartzites, granites, gneiss, dolomites, mica-schists, phyl- lites [17] and Dhanjori groups of volcanic rocks. Kharkai river, most important tributary of the river Subarna- rekha, passes through one of the most important industrialized belts of Asia (Adityapur industrial area) and joins it near Sonari towards north-western periphery of the steel city Jamshedpur. In addition, Kanchi, Karkari, Garra, Gurma and Sankh are other significant tributaries that make the river basin. Downstream of the Jamshedpur city Garra, Gurma and Sankh rivers pass through key mining belts and join the river Subarnarekha at different places. Many heavy mining and processing belts, industrial conglomerates and populated areas are located along the ba- sin which make river Subarnarekha as the main receiving body of industrial discharges, mine drainages, partially treated or untreated domestic wastes etc.

Sediment samples were collected from seventeen selected locations along the Subarnarekha river (Figure 1) during May, 2011 (pre-monsoon) and November, 2011 (post-monsoon) periods. Sampling sites were selected based on surveys, that is, areas having high anthropogenic activities and areas relatively free of anthropogenic influences, and accessibility. Surface sediment samples (3 grabs per sample) were taken at a depth of about 5 cm

and immediately transferred into pre-cleaned polythene bags [18] . The collected samples were oven dried at 40˚C for 48 hours; passed through a 1 mm plastic sieve to remove plant parts, debris and gravel-sized materials; and then sieved through a nylon sieve (aperture 125 µm). Use of fractions <125 µm for characterization of the bed sediments has also been reported earlier [3] [15] . The lower particle size sediment fractions were ground using mortar and pestle for homogenization and prepared for further analysis of physicochemical properties and concentration of six elements [19] . All necessary precautions and care were taken during drying, sieving, grind- ing and storage of sediment samples to avoid any kind of contamination.

The pH of the sediment samples was measured using a digital pH meter (pHTestr 30, Eutech instruments, Oak- lon) in 1:2.5 sediment to water ratio. The suspension was allowed to stand overnight prior to pH measurement [3] . Electrical conductivity (EC) was determined using Systronics Conductivity Meter (Model 361) in sediment saturation extracts as described by [20] . Organic Carbon (OC) was measured by partial oxidation method as out- lined by [21] . Widely used HNO₃ + HClO₄ acid digestion procedure for total element analysis in sediment sam- ples and as described by [22] was carried out. Briefly 1 gm of sample was digested on hot plate with acid mix- ture containing 10 ml of concentrated HNO₃ and 5 ml 70% HClO₄. After cooling, the mixture was boiled with 20 ml distilled water to release any fumes. The digested samples were filtered through Whatman No. 42 filters and made up to 25 ml by adding distilled water in a volumetric flask. Concentrations of six elements, namely, Fe, Zn, Cu, Pb, Cd and Mn were determined with Atomic Absorption Spectrophotometer (AAS: Varian AA50) at wavelengths (nm)―Fe = 248.3, Zn = 213.9, Cu = 324.8, Pb = 217, Cd = 228.8, Mn = 279.5. Before running sample analysis, the AAS was subjected to calibration and standardization using appropriate standards. The ba- sis of element quantification was calibration curves of standard solution of elements (Fe: HC001722, Zn: HC117124, Cu: HC114735, Pb: HC125468, Cd: HC123670, Mn: HC241921) purchased from Merck (KGaA), Germany. To check the accuracy of the data, calibration was verified by analyzing a midpoint calibration stan- dard and a calibration blank with each batch of samples run. Reagent blank, prepared to assess presence of ana- lytes or interference, was found to be devoid of any analytes. The analytical precision was also verified by run- ning one replicate and one blank spike sample after each batch of sample [7] . The accuracy of the procedure was also checked running five replicates of the standard solution of each element (expressed as mean ± standard deviation)―Fe: 0.998 ± 0.053, Zn: 0.55 ± 0.029, Cu: 0.126 ± 0.014, Pb: 0.22 ± 0.021, Cd: 0.049 ± 0.0045, Mn: 0.254 ± 0.027. The glassware were washed with 14% HNO₃ and rinsed thoroughly with Milli-Q quality water prior to use. The Milli-Q quality water was used throughout the experiments. All the chemicals and reagents used were of analytical grade purchased from Sigma-Aldrich (USA) and Merck (Germany and India). The raw data were subjected to basic statistical analysis to identify some descriptive statistical factors. Interrelationships between variables were determined by correlation analysis applying Pearson correlation coefficient.

In the present study six indices, namely, contamination factor (CF), contamination degree (CD), pollution load index (PLI), enrichment factor (EF), geo-accumulation index (Igeo) and potential ecological risk index (PERI) were prepared and evaluated stepwise to determine degree of anthropogenic influence on the sediment quality. An integrated index is a collection of single indices determined separately and then combined to designate the overall quality of the sediment. Three integrated indices, namely, PLI, CD and PERI were used in this study. Methods of calculation and classification criteria of studied indices with references are presented in Table 1. CF, PLI and CD calculations involve comparing concentration of elements with their geochemical background ref- erence value and then computing the indices. While CF is calculated for individual elements, CD and PLI pro- vide overall information about the sediment contamination of study sites. Similar to CF, Igeo [27] is also com- puted for individual elements which supply valuable knowledge about the degree and extent of element load in the sediments. EF, as introduced by [25] , is used to assess the degree of anthropogenic influence on element load in the sediments, and also to differentiate between elements originating from the natural or anthropogenic activi- ties [9] . PERI, originally developed by [23] , provides a mean to quantitatively evaluate ecological risk posed by multiple element pollutions in the bed sediments of aquatic systems [30] . It takes into account concentration of elements, their potential ecological risk factors (PERF), and the sedimentological toxic response factors (TRF). TRF assigned to elements used in the calculation of PERI are: Cu = Pb = 5; Cd = 30; Zn = 1 [29] . Due to ab-

CF = Contamination Factor; PLI = Pollution Load Index; CD = Contamination Degree; EF = Enrichment Factor; Igeo = Geo-Accumulation Index; PERI = Potential Ecological Risk Index; Co = Observed Element Concentration; C_b = Background Concentration of the Element; M = Element; R = Reference Element; B_n = Background Concentration; = Monomial Ecological Risk Index; = Toxic Response Factor.

sence of any background concentration of elements from the studied area, average shale standards of trace ele- ments described by [31] were taken as geochemical reference values in the present study. Fe was employed as normalization element to calculate EF values due to its abundance and controlling influence on the distribution of other trace elements [32] [33] . Based on positive correlations between sediment chemistry and sediment tox- icity, [34] explained consensus-based sediment quality guidelines (SQGs) for classifying sediments as toxic and not-toxic. According to authors, SQGs are important tools for identifying contaminated sediment hotspots and also for assessing possible effects of contaminated sediments on benthic organisms. Threshold effect concentra- tion (TEC) and probable effect concentration (PEC) are commonly employed for sediment contamination inves- tigations with respect to elements [1] [35] as these guidelines provide predictive ability of adverse biological ef- fects to the sediment dwelling fauna and other aquatic organisms [35] . TEC is defined as the concentration be- low which adverse effects are unlikely to be observed whereas PEC denotes concentration above which adverse effects are frequently expected to occur [34] . Another tool developed to study sediment toxicity is the mean se- diment quality guideline quotients (mSQGQs). In the present study mSQGQs were derived following [36] . The quotients were, however, adjusted and derived from four analytes: Zn, Cu, Pb and Cd. The methodology em- ployed to investigate Subarnarekha river bed sediments is schematically represented in Figure 2.

The pH, EC and OC (%) values obtained in the sediments of the river Subarnarekha during pre-monsoon study are displayed in Table 2; a summary of post-monsoon data of these measured parameters is also given in Table 3. The pH values ranged from 5.76 to 6.83 and 5.91 to 6.81 during pre-monsoon and post-monsoon periods re- spectively indicating slightly acidic nature of the sediments. This might have resulted from the formations of humic acid substances as well as discharge of acidic industrial, mining and domestic wastes into the river. EC of the sediment implies ability of the sediment to conduct electric current [37] . Lowest EC value was obtained at S1, which is a comparatively non-polluted site, while highest EC was recorded at S14 during both periods of study. Post-monsoon sediments had higher EC level (0.153 - 1.147 ms/cm) than pre-monsoon sediments. OC values ranged from 2.97% to 5.34% during pre-monsoon and showed almost similar pattern in the second study period. Significantly higher values of OC were observed at S9, S14 and S15. In addition to adsorption and other related processes, elements are also incorporated into the sediment by organic complexation. Organic materials from river water and decomposed matter get enriched into the sediment [38] . However, smaller fractions of se- diments display more efficient relationship with OC as compared to larger fractions.

Concentrations of six studied elements recorded in collected surface sediments (of pre-monsoon season) from the Subarnarekha river are displayed in Table 2; a summary of post-monsoon data of the elements is also given in Table 3. Elements displayed wide variations in their distribution suggesting control of anthropogenic activi-

^aStandard deviation; ^bConsensus based sediment quality guidelines (CSQGs).

Values of pH in pH units; EC in mS/cm; OC in %; elements in mg/kg; Min = Minimum; Max = Maximum.

ties on sediment chemistry. Although similar spatial variability of elements was recorded for the Subarnarekha river sediments in both pre-monsoon and post-monsoon periods, the latter displayed higher concentration load than the former. This could be due to more runoffs from industrial, mining, urban and agricultural areas during rainy season. Elements released into aquatic environments become bound to the particulate matters which in due course settle down and become part of the sediments [10] . Overall concentration of trace elements followed the order: Fe > Mn > Cu > Zn > Pb > Cd. The sampling site S14 recorded highest concentration of Fe, Zn, Cu, Pb and Cd while S9 showed maximum Mn value. Four sampling stations S8, S9, S14 and S15 regularly displayed more element concentrations compared to others. S8 and S9 are located in the Jamshedpur city, a highly popu- lated and industrialized belt of Jharkhand. Moreover, river Kharkai, which carries industrial and domestic wastes from the Adityapur industrial area, one of the largest in Asia, joins the river Subarnarekha near S8. The river at S14, located nearby a copper factory site and upstream of Ghatsila town, and S15, situated downstream of Ghat- sila, is a major industrial and domestic discharges receiving body. Sampling sites located nearby industrial, mining and urban areas either exceeded TEC with respect to Cd, Pb, Cu and Zn or closely approached the benchmark, while for PEC, concentration of elements at sampling sites S14 and S15 was relatively very high. Analyzed appraisal with SQGs (TECs and PECs) and the results of temporal study indicated adverse eco-toxic effects from long term exposure of elements which was more alarming for Cd. Elements also exceeded their av- erage shale standard concentrations in sampling sites characterized by high anthropogenic activities. More pro- nounced results were obtained at S7, S8, S9, S14 and S15 where elements surpassed their geochemical back- ground values as high as forty seven times indicating high enrichment of sediments with elements. Accumula- tion of elements in bed sediments of the river Subarnarekha as compared to some other river sediments around the world, even though each area has its own geochemical characteristics, indicate higher load for Fe, Cu and Mn and substantial enrichment for Cd (Table 4). The spatial and temporal investigation revealed Cd as the big- gest contaminant and chief cause of concern. Cd concentration was noted above its geochemical background value throughout the studied area in both study periods; however, its concentration was significantly higher at sites characterized by dominant anthropogenic activities. Contamination of sediments of freshwater systems with Cd is increasingly becoming a major problem in developing countries worldwide. Some cases include: Gomti river (India) 0.70 to 7.90 mg/kg [40] ; Achankovil river (India) 3.67 to 11.43 mg/kg [7] ; Hindon river (In- dia) 1.30 to 3.28 mg/kg [10] ; Buriganga (Bangladesh) 3.5 to 7.8 mg/kg and 4.1 to 9.5 mg/kg in summer and winter seasons respectively [43] , Lianshan and Wuli rivers (China) 25.53 to 98.78 mg/kg and 8.04 to 17.75 mg/kg respectively [30] . Not only rivers, Cd contamination are also being recorded for the wetland systems. For examples, Bangalore urban lakes (India) recorded 4.68 to 14.25 mg/kg Cd [44] and Vembanad wetland system in Kerala (India) 0.26 to 0.73 mg/kg [1] . Results of only one season (pre-monsoon) are displayed in tables and figures, unless otherwise mentioned.

^a[39] ; ^b[40] ; ^c[7] ; ^d[37] ; ^e[41] ; ^f[10] ; ^g[33] ; ^h[42] ; ⁱ[31] ; All values in mg/kg.

CF is used to illustrate the contamination of particular toxic substance at a given site [1] . The characteristic ter- minologies of CF and its calculated values in the sediment samples from the Subarnarekha river are given in Table 1 and Table 5 respectively. S14 displayed moderate contamination for Fe; considerable contamination for Zn; moderate contamination for Pb; and very high contamination for Cd and Cu in both pre-monsoon (10.27 and 47.15) and post-monsoon periods (15.97 and 48.55) indicating serious anthropogenic contribution to the conta- mination load of sediments at this site. Meanwhile contaminations of sediments, with reference to one or more elements, were also reported from S2, S6, S7, S8, S9, S12 and S15. Of the two study periods, the sediment was more contaminated in post-monsoon period. Trace element Cd revealed as the most severe component causing moderate to very high contamination of the sediments in both periods of study. Similar pattern was noted for contamination degree (CD) (Figure 3(a)), where sampling sites having dominant anthropogenic activities dis- played high CD. This demonstrates regular monitoring of the sediments for the presence of trace elements espe- cially cadmium is required. In geochemical investigations, PLI is used as a resourceful tool to measure and compare sediment contamination. Analyzed sediments at S7 (1.231), S8 (1.158) and S9 (1.524) towards up- stream segment, and S14 (4.337) and S15 (1.407) towards downstream region displayed higher PLI values and progressive deterioration in quality (Figure 3(a)). S14 recorded highest PLI closely followed by S15. Compara- tively higher PLIs (0.293 - 5.069) were noticed in post-monsoon study (Table 3), which indicated more enrich- ment of metals. Higher PLI values in sediments demonstrated substantial anthropogenic impacts on the sediment quality whereas lower PLI values pointed to no considerable anthropogenic activities. This investigation streng- thened employment of CD and PLI as effective instruments for assessing the environmental geochemistry of se- diments and could be used individually or in combination as they closely complemented each other. Moreover, they easily convey information to the public and policy makers to ascertain the contamination load of the sedi- ments to take necessary remedial measures. To measure degree and extent of element contamination in freshwa- ter resources EF and Igeo can also be used as reference systems [10] . Geo-accumulation index consists of a seven grade sediment quality classification scheme varying from uncontaminated to extremely contaminated

categories. According to [40] Class 6 indicates 64 fold enrichment above the geochemical background value. The EF and Igeo values calculated for studied elements in all sediment samples and variations obtained (pre- monsoon data) are graphically presented in Figure 3(b) and Figure 3(c) respectively. A brief post-monsoon summary of these indices is also given in Table 3. The EF and Igeo exhibited similar spatial variations in both study periods; however, temporally post-monsoon period was more contaminated. Analysis of results displayed sediment samples collected from urban-industrial areas enriched with Cu and Mn. Sites S7 and S15 showed moderate enrichment for Cu while S14 demonstrated significantly high enrichment for the element. Moderate enrichment for Mn was noted at S8, S9 and S12. Sediments of Subarnarekha were found to be uniformly en- riched with Cd which varied from moderate to significant enrichment. However, with some exceptions, sam- pling sites dominated by industrial, mining and other anthropogenic activities presented elevated Cd enrichment. Analyzed results showed sediment at S14 was moderately contaminated with Fe and Zn. The Igeo of Cu varied from uncontaminated to extremely contaminated, and the latter was recorded at S14 (+5.045). Sediments of S7 and S15 suggested uncontaminated to moderate contamination of Cu. For Pb only S14 exhibited some degree of contamination. Presence of Cd again demonstrated severe contamination of the Subarnarekha sediments where its Igeo ranged from +0.152 (S4) to +2.775 (S14).

The indices mentioned above deal with anthropogenic input and estimate contamination not toxicity. While contamination is related with anthropogenic input, pollution describes toxicity. As lucidly explained by [45] , the contamination is said to happen when a substance is present where it should not occur in general or at concen- trations above the background level. On the other hand, pollution is that contamination that can cause adverse biological effects to the natural biotic communities. Thus, in addition to quantify accumulation of trace elements in sediments and apportion anthropogenic impacts, a tool is needed to express potential effects of presence of multiple elements in the sediments, that is contamination situation, on ecological risks or harm to the local eco- system [29] [30] . Potential ecological risk index (PERI) and also SQGs can be applied in ecological risk as- sessments of trace element pollutants in soils and sediments. However, SQGs (as described earlier) are element- specific and do not take into account multiple element mixtures which are normally expected in the environ- mental studies. These are used for initial determination to assess whether or not contaminants of potential con- cern could cause any harm to the receptors of potential concern [45] . To overcome this gap mSQGQs have been developed; which involve chemical mixtures normalized to their appropriate SQGs to determine biological ef- fects. [36] expressed a broad range of toxicity incidence, between low (<0.1) and high (>2.3), based on their mSQGQ method. We recalibrated their toxicity quotients based on average (%) survival of amphipods and de- veloped a new modified terminology on mSQGQ classification system, which can be expressed as: <0.1 (very low incidence of toxicity), 0.1 - 0.25 (low incidence of toxicity), 0.25 - 1.0 (moderate incidence of toxicity), 1.0 - 2.3 (high incidence of toxicity) and >2.3 (extremely high incidence of toxicity). Sampling site S14 displayed adjusted mSQGQ very close to high incidence of toxicity (0.813) during post-monsoon season which was almost 2.3 times than the pre-monsoon value (0.359). According to [35] SQGs should be applied either as a screening approach or a weight-of-evidence procedure for the risks associated with the contaminated sediments. An integrated index system like PERI provides more valuable insights into eco-toxicological effects of elements polluting bed sediments. Except five non-polluted sites, the PERI of studied sediments varied from moderate risk to significantly high risk (116.98 - 556.83) during pre-monsoon period, indicating that sediments in the Subarnarekha river were exceedingly polluted by elements (Figure 4), especially present in discharges of indus- trial and urban wastes. The river showed similar spatial distribution of ecological risk in post-monsoon period; however, corresponding PERI recorded was higher which varied from 128.76 - 738.43. Cd displayed highest monomial potential ecological risk, which varied from 50.01 to 308.01 (pre-monsoon) and 54.00 to 479.01 (post-monsoon) followed by Cu (235.74 - 242.75) at S14. Analyzed results always showed pronounced Cd con-

tribution in PERI of bed sediments because of its higher toxicity response factor as compared to other elements and excessive enrichment. Authors like [29] [30] [46] in their studies on soils and sediments have also demon- strated enhanced role of Cd in causing ecological risks. Acute toxicity due to Cd in the Subarnarekha bed sedi- ments would be expected at 64% of the sites. Assessment of distribution and degree of accumulation of Cd and other elements in bed sediments not only provide information on anthropogenic enrichment, but also potential ecological risks associated with their exposure. Enrichment of Cd and other elements in aquatic beds can affect entire range of biotic spectrum ranging from benthic biota to the organisms higher up the food chains due to their persistence, bio-accumulative and injurious properties. In aquatic ecosystems both abiotic and biotic com- ponents continuously interact with each other and presence of toxic elements beyond the restoring capacity can severely impact the ecological functioning of the aquatic systems in long term, which in short term may not be visible to us. Here, it should also be noted that, although, both PLI and PERI are based on CF values, the former does not take into account any sedimentological toxicity factor whereas the latter uses a toxicity factor for its computation. PLI portrays contamination situation and not ecological risk, and therefore, we suggest, the term PLI should be replaced with CLI (contamination load index). The clear-cut definitions of contamination and pollution also support this observation.

Correlation analyses are commonly employed to determine relationships between physicochemical compo- nents as well as identification of factors and sources of variables. Results of Pearson correlation analysis applied in the present investigation and the corresponding matrix generated are displayed in Table 6. Most of the ele- ments showed strong correlation with OC at P < 0.05 and P < 0.01 suggesting presence of organic matter influ- enced elements’ accumulation in the sediments. Impact of organic pollution load in causing enhanced element enrichment in bed sediments was also reported for the Hindon river in India [10] . Elements showing signifi- cantly high relationship in correlation analysis may indicate same origin and controlling factors [47] . Very strong correlation was noticed between Fe and most of the elements (Zn, Cu, Pb and Cd) at P < 0.01 suggesting some common sources of elements in the Subarnarekha. In addition to industrial effluents and urban wastewater, possibly urban runoffs and atmospheric deposition were also contributing to the element pollution of the river. Moreover, as the river basin has rich occurrence of ores containing Fe, Zn, Cu and Pb, their chemical weathering and leaching might also be contributing elements in the sediments. However, elevated concentrations and do- minance of these elements at industrial hubs and predominantly urban regions like S7, S8, S9, S14 and S15 re- vealed that industrial and other anthropogenic activities were overwhelmingly responsible for the presence of these elements in the bed sediments. Similarly strong correlation was noted between Zn, Cu, Pb and Cd at P < 0.01 demonstrating elements had a common source. Meanwhile, positive correlation was also noticed between Cu, Pb and Cd (P < 0.01). The common presence of Cd in correlation analysis indicated that the element had chiefly anthropogenic origin. Towards upper reaches application of mineral fertilizers and consequent agricul- tural runoff were principally responsible for its presence in river. [48] observed higher concentrations of Cd in upper reaches of Siahroud river from agricultural use of phosphorus, zinc and iron fertilizers. The element is used in electroplating, batteries, paints, pigments and in alloys with a range of other elements and also occurs in

^*Correlation is significant at the 0.05 level (two tailed); ^**Correlation is significant at the 0.01 level (2-tailed).

sulphide minerals containing Zn, Pb and Cu [49] . Also overall concentration of Cd was reported to be four times its geochemical background. However, no significant relationship was observed for Mn with any other element, possibly because unlike other elements Mn had different sediment deposition features [10] . The Subarnarekha river from its origin to the border of Jharkhand (with West Bengal) receives effluents and discharges of big and small industrial conglomerates, populated urban areas and extensively mined regions. Additionally, open dump- ing of garbage beside river banks and washing of automobiles and vehicles in river water are making sediments of Subarnarekha increasingly contaminated.

Degradation of river bed sediment quality portrays river degradation as a whole because it is the outcome of river water pollution. The problem of river basin degradation is more pronounced in developing countries be- cause expanding economic growth puts terrific pressure on the limited available natural resources. As per the assessment of the renowned economic consultancy the Centre for Economics and Business Research (CEBR) in World Economic League Table Report, the Indian economy, which presently holds 11^th position in the world, is growing very fast, and by 2028, it is expected to become the 3^rd largest economy after China and United States [50] overtaking Japan. Meanwhile, the population of India is also expected to surpass 1.45 billion. Thus, to sa- tisfy the demand of the growing population along with the economic growth, massive industrialization, urbani- zation, changes in land use pattern and intensive agriculture are inevitable. All these activities, in turn, will af- fect river basins if complete attention is not given. The Subarnarekha basin will have more alarming situation because, according to the International Water Management Institute (IWMI, Colombo, Sri Lanka) research re- port, currently its population density (347 persons per km²) is already much ahead of the national average of all river basins (282 persons per km²), and in terms of some major river basins it lies only behind Sabarmati (521), Ganges (449) and Cauvery (389) [51] . The information obtained through this research communication, based on systematic investigation of the sediment quality, provides valuable insights for result-oriented environmental management of the industrial, urban, mining and mineral processing regions. Some immediate requirements on effective management policies and conservation strategies are needed to prevent the current contamination situation developing into pollution problems all through the river basin.