Geochemistry of Rare Earth Elements in Sediment of Central India ()
Received 30 January 2016; accepted 15 April 2016; published 18 April 2016
1. Introduction
The rare earth elements (REE) including actinide have wide industrial applications in several fields i.e. nuclear energy as fuel and modifier, organic synthesis as catalyst, ceramics as coloring agents, X-ray tubes as phosphors, etc. [1] [2] . The distribution of REE in various environmental materials i.e. soil and sediments was reported [3] - [13] . Recently, the health hazards of the REE were highlighted [14] [15] . The environment of the Ambagarh Chowki block, central India is seriously contaminated with As and heavy metals [16] . In this work, the geochemistry of the REE in pond sediments of Ambagarh Chowki block, Rajnandgaon district, central India is described.
2. Materials and Methods
2.1. Study Area
Arsenic and other heavy metals are deposited in the environment of Ambagarh Chowki block, Rajnandgaon district, Chhattisgarh, India over area »3000 km−2. The Ambagarh Chowki block falls in a tribal belt with population of ≈0.1 million. This block covers 155 villages and towns which suffering with serious health hazards due to contamination of the environment with toxic elements. In this work, 24 ponds lie in different 11 villages (locations) of Ambagarh Chowki block were selected for the investigation of the REE contamination (Figure 1).
2.2. Sampling
The composite surface sediment sample (0 - 10 cm) was collected from five points in the equal ratio from each pond as prescribed in literature [17] . For the depth profile studies, the samples at the depth profile of 0 - 10, 10 - 20 and 20 - 30 cm of the Bhadsena pond was collected.
2.3. Analysis
The samples were dried, crushed and sieved out the particles of size ≤ 1 mm. A 0.25 g of each sediment sample was digested with 8 ml aqua regia in the closed microwave vessel for 15 min. An aliquot of the extract was diluted with deionized water for the further analysis. The Thermo Fisher ICP-OES and ICP-MS (Polish Geological Institute, NRI, Central Chemical Laboratory, and Warsaw) were employed for analysis of the elements. The NCS DC 73382 CRM sediment sample was used for the quality control. The background levels of the REE reported in the upper earth crust were used for computation of the enrichment factor (Ef) by using following equation [18] .
where, Xs, Als, Xe and Ale are concentrations of metal and Al in the soil and earth crust, respectively.
3. Results and Discussion
The sediment was found to be colored from light brown (LBr) to dark brown (DBr), Table 1. The pH value of the extract was ranged from 6.5 - 8.1 with mean value of 7.2 ± 0.2.
3.1. Concentration of Elements
The concentrations of 49 elements in 24 pond sediments are shown in Tables 1-4. The concentration of elements i.e. Fe, Al, Ca, Mg, K, Mn, Ti, Na, P, S, Ba, V, Zn, Cu, As, Ni, Cr, Co, Sr, Pb, Rb, Ga, Li, Be, Mo, Ag, Cd, Sn, Sb, Cs, Bi, Th, U, Sc, Y, La, Ce, Pr, Nd, Eu, Sm, Gd, Tb, Dy, Ho, Er, Tm, Tb and Lu was ranged from 25,400 - 65,900, 11,800 - 34,700, 1500 - 16,100, 1500 - 30,200, 1200 - 4500, 256 - 1660, 62 - 735, 90 - 830, 90 - 570, 50 - 790, 88 - 304, 29 - 166, 32 - 100, 28 - 89, 10 - 53, 19 - 340, 24 - 1298, 9 - 76, 10 - 69, 10 - 40, 12 - 46, 7 - 15, 5 - 18, 0.9 - 3.4,0.14 - 1.32, 0.07 - 2.36, 0.05 - 0.39, 0.8 - 2.6, 0.27 - 0.97, 0.5 - 2.2, 0.10 - 0.30, 6.1 - 25, 0.5 - 1.9, 3.0 - 25, 11 - 61, 16 - 119, 41 - 163, 4.0 - 28, 16 - 99, 0.7 - 2.7, 3.2 - 18, 2.7 - 16, 0.4 - 2.3, 2.2 - 13, 0.4 - 2.4, 1.1 - 6.1, 0.15 - 0.83, 0.9 - 4.8 and 0.13 - 0.70 mg/kg with mean value of 44842 ± 5133, 23813 ± 2819, 5133 ± 1418, 6850 ± 2581, 2708 ± 243, 759 ± 158, 254 ± 79, 355 ± 93, 268 ± 45, 285 ± 81, 196 ± 21, 84 ± 16, 63 ± 7, 52 ± 6, 22 ± 5, 75 ± 30, 177 ± 118, 30 ± 7, 26 ± 6, 23 ± 3, 26 ± 3, 11 ± 1, 12 ± 2, 1.6 ± 0.2, 0.63 ± 0.14, 0.67 ± 0.23, 0.13 ± 0.03, 1.5 ± 0.2, 0.44 ± 0.05, 1.2 ± 0.2, 0.15 ± 0.03, 11 ± 2, 1.1 ± 0.1, 11 ± 2, 20 ± 4, 42 ± 8, 42 ± 8, 89 ± 13, 9 ± 2, 34 ± 7, 1.2 ± 0.2, 6.3 ± 1.2, 5.4 ± 1.0, 0.77 ± 0.15, 4.2 ± 0.8, 0.8 ± 0.2, 2.0 ± 0.4, 0.27 ± 0.05, 1.6 ± 0.3 and 0.24 ± 0.04 mg/kg, respectively. Among them, the highest concentration of Fe was marked. They occurred in following decreasing order in the sediment: Fe < Al < Mg < Ca < K < Mn < Na < S < P < Ti < Ba < Ce < Cr < V < Ni < Zn < Cu < La < < Nd < Co < Sr » Rb < Pb < As < Y < Li < Ga » Th » Sc < Pr < Sm < Gd < Dy < Er < Yb » Be < Sn < Eu » Cs < U < Tb » Ho < Ag < Mo < Sb < Tm < Lu < Cd » Bi.
3.2. Concentration of REE
The concentration of the LREE (i.e. La, Ce, Pr, Nd, Eu and Sm) and HREE (i.e. Gd, Tb, Dy, Ho, Er, Tm, Yb
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Table 1. Concentration of major element in sediments, mg/kg.
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Table 2. Chemical characteristics of metal in pond sediment, mg/kg.
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Table 3. Chemical characteristics of minor element in pond sediment, mg/kg.
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Table 4. Concentration of lanthanide in pond sediment, mg/kg.
and Lu) was ranged from 82 - 431 and 8 - 46 mg/kg with mean value of 182 ± 30 and 15 ± 3 mg/kg, respectively. The ratio of LREE/HREE and Lu/Y was found to be in the range of 9 - 18 and 14 - 56 with mean value of 12 ± 1 and 27 ± 4, respectively. The concentration of REE and LREE/HREE and Lu/Y ratio were found to be higher than values reported in river sediments of the other regions of the World [3] - [11] .
The concentration of Th and U in the sediments (n = 24) was ranged from 6.1 - 25 and 0.46 - 1.86 mg/kg with mean value of 11 ± 2 and 1.14 ± 0.13 mg/kg, respectively. The Th/U ratio was ranged from 6 - 28 with mean value of 11 ± 2. The concentration of actinide elements in the studied area was found to be comparable to values reported in soil of other regions of the country [12] [13] (Figure 2).
3.4. Spatial Variations and Sources
The sediment samples were collected from 24 ponds which situated in 11 locations (i.e. villages) of Ambagarh Chowki block. The content of the REE in the pond sediments of 11 locations are shown in Figure 3. The highest content of the REE in the pond sediment of Bhadsena was observed. The REE content in sediment was found to increase as the depth profile was increased from 0 - 30 cm, may be due to geogenic origin and less binding with organic components of the sediment, Figure 4.
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Figure 1. Representation of sampling locations (i.e. Murethitola-1, Murethitola-2, Murethitola- 3, Netamtola- 1, Netamtola-2, Netamtola-3, Kaudikasa-1, Kaudikasa-2, Kaudikasa-3, Ghorda-1, Ghorda-2, Ghorda-3, Metepar-1, Metepar-2, Metepar-3, Bhadsena, Sonsaitola-1, Sonsaitola-2, Sonsaitola-3, Meregaon, Joratarai,Thailitola-1,Thailitola-2 and Jadutola) in Ambagarh Chowki.
The correlation matrix of the REE is summarized in Table 5. All REE inclusive of Eu, Th and U are correlated well in the sediment, indicating origin from the similar sources likely to geogenic origin. They were partially correlated with elements i.e. Be, K, Rb, Cs, Mo, As, Sb, Bi, Sn, and Ag. Their negative correlations with elements i.e. Na, Mg, Ca, Ba, Sr, Al, Ga, V, Cr, Fe, Mn, Co, Ni, Cu, Zn, Cd and Pb were observed.
3.5. Enrichment
The Ef value for Sc, Y, La, Ce, Pr, Eu, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th and U in the sediment was ranged from 0.8 - 4.2, 1.5 - 9.4,1.7 - 13, 1.4 - 12, 1.7 - 13, 1.6 - 9,1.7 - 12, 1.6 - 12, 1.9 - 13, 1.6 - 11,1.6 - 11, 1.6 - 9, 1.4 - 9, 1.4 - 9, 1.4 - 8, 1.1 - 7, 1.1 - 11 and 0.4 - 3 with mean value of 2.5 ± 0.4, 4 ± 1, 6 ± 1, 5 ± 1, 5 ± 1, 4
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Figure 2. Spatial variation of REE concentration in sediment of Ambagarh Chowki.
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Figure 3. Spatial variation in concentration of actinide in sediment.
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Figure 4. Depth profile studies of elements in Bhadsena pond sediment. D1 = 0 - 10 cm, D2 = 10 - 20 cm, D3 = 20 - 30 cm.
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Table 5. Correlation matrix of REE.
± 1, 5 ± 1, 5 ± 1, 5 ± 1, 4 ± 1, 4 ± 1, 4 ± 1, 3 ± 1, 3 ± 1, 3 ± 1, 3 ± 1, 4 ± 1 and 1.7 ± 0.3, respectively. They were moderately enriched in the sediment. Their highest enrichments were marked in sediment of the Bhadsena village.
4. Conclusion
The REE were moderately enriched in all ponds and their enrichments were found to decrease as the mass number of the REE was increased. The concentration of all REE in the sediment was increased vertically, may be due to origin from the rock weathering. Their highest contents were marked in the sediment of Bhadsena village, Rajnandgaon, India.
Acknowledgements
We are thankful to the Alexander von Humboldt Foundation, Bonn for financial support to one of author: KSP. Our sincere thanks are also extended to the UGC, New Delhi for awarding Rajiv Gandhi Scholarship to students: BLS, KPR and SR.
NOTES
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*Corresponding author.