|Year : 2017 | Volume
| Issue : 1 | Page : 21-26
Heavy metal assessment in sediments of east coast of Tamil Nadu using energy dispersive X-ray fluorescence spectroscopy
N Harikrishnan1, R Ravisankar1, M Suresh Gandhi2, KV Kanagasabapathy3, M. V. R. Prasad3, KK Satapathy3
1 Department of Physics, Government Arts College, Tiruvannamalai, Tamil Nadu, India
2 Department of Geology, University of Madras, Guindy Campus, Chennai, Tamil Nadu, India
3 Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu, India
|Date of Submission||24-Oct-2016|
|Date of Decision||13-Feb-2017|
|Date of Acceptance||08-Mar-2017|
|Date of Web Publication||24-Apr-2017|
Department of Physics, Government Arts College, Tiruvannamalai - 606 603, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Selected heavy metals (Cr, Co, Ni, Cu, Zn, As, and Pb) in sediments from Periyakalapattu to Parangipettai of east coast of Tamil Nadu were determined to assess the contamination status and potential ecological risk. The pollution indices such as enrichment factor (EF), contamination factor (CF), geoaccumulation index (Igeo), and pollution load index (PLI) were calculated to determine the contamination level and enrichment of metals in sediments. EF analysis suggested that anthropogenic influence on the environment has been significant in case of Cr. The values of CF indicate that the sediments are not contaminated with these heavy metals. Igeoresults reveal that the study area is not contaminated with respect to Cr, Co, Ni, Cu, Zn, As, and Pb. This results of Igeoare in good agreement with PLI. Based on the sediment quality guidelines, it is observed that Cr and Ni would be a concern for the ecotoxicological risk in study area.
Keywords: Energy dispersive X-ray fluorescence, pollution indices, potential ecological risk, sediment
|How to cite this article:|
Harikrishnan N, Ravisankar R, Gandhi M S, Kanagasabapathy K V, Prasad M, Satapathy K K. Heavy metal assessment in sediments of east coast of Tamil Nadu using energy dispersive X-ray fluorescence spectroscopy. Radiat Prot Environ 2017;40:21-6
|How to cite this URL:|
Harikrishnan N, Ravisankar R, Gandhi M S, Kanagasabapathy K V, Prasad M, Satapathy K K. Heavy metal assessment in sediments of east coast of Tamil Nadu using energy dispersive X-ray fluorescence spectroscopy. Radiat Prot Environ [serial online] 2017 [cited 2018 Nov 15];40:21-6. Available from: http://www.rpe.org.in/text.asp?2017/40/1/21/205056
| Introduction|| |
The rapid industrialization in the coastal area increases the heavy metal contamination in sediment samples. Sediments are ecologically important components of the aquatic habitat and are also a reservoir of contaminants, which play a significant role in maintaining the trophic status of any water body. Expanding industrial activity over recent decades has regularly introduced heavy and toxic metals, fertilizers, or pesticides in any ecosystem. Since the industrial revolution, considerable amounts of the toxic pollutants were discarded into coastal environment, and sediments of bays and estuaries have huge sinks of heavy metals. More than 90% of the heavy metal load in the aquatic systems were found to be associated with suspended particulate matter and sediments.
Sediments act as sinks and sources of contamination in aquatic systems because of their variable physical/chemical properties. Naturally, the sediments contain major elements (Mg, Al, Si, K, Ca, Ti, and Fe) due to earth crust and toxic metals (V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Ba, La, and Pb) due to anthropogenic activities.
The coastal sediments provide useful information about environmental and geochemical nature of the marine environment. They are composite minerals consisting of inorganic components, mineral particulates, and organic matter in various stages of decomposition. Sediment pollution by heavy metals is regarded as a critical problem in marine environment because of their toxicity, persistence, and bioaccumulation. Many studies have shown that heavy metals in sediments could have a significant negative impact on the health of marine ecosystems. Knowledge about distribution and concentration of heavy metals in sediments used to detecting their sources in aquatic systems. Therefore, heavy metal distributions in sediments offer a more realistic approach of evaluating their actual environmental impact.
Energy dispersive X-ray fluorescence (EDXRF) is a dominant analytical tool for elemental composition assessment of environmental samples in particularly soil and sediments.,,,, This is nondestructive and multi-elemental in nature with a large throughput of samples. In the present work, EDXRF is used for large area screening as it is fast and requires small quantity of a sample.
Therefore, it is important to study heavy metal contamination, distribution, and their possible sources of sediments in the study area. The present study is aimed to (1) determine the levels of heavy metals (Cr, Ni, Pb, Co, As, Cu, and Zn) in the sediments, (2) identify the possible sources of these metals, (3) determine the enrichment and contamination status of metals using pollution indices, and (4) assess potential ecological risk and ecotoxicological significance of metal concentrations in sediments by potential ecological risk method and sediment quality guidelines (SQGs).
Sediment samples were collected along the Bay of Bengal coastline, from Periyakalapattu to Parangipettai coast during the premonsoon condition. [Table 1] gives the geographical latitude and longitude for the sampling locations. Representative samples were collected from all sampling locations. Recent industrial developments in the study area in particularly, Cuddalore, Auroville, Thazhankuda, and Sitheripettai coastal towns, include offshore oil production, chemical, fertilizer processing plants, and more than 100 small scale industries.
|Table 1: Geographical latitude and longitude of sampling locations at the study area|
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| Materials and Methods|| |
Sample collection and preparation
Sediment samples were collected using a Peterson grab sampler parallel to the shoreline. [Figure 1] shows the location map of the study area. Uniform quantities of sediment samples were collected from all the sampling stations. Sediment samples were stored in plastic bags and dried at 105°C to a constant weight. Then, samples were ground into a fine powder using an agate mortar. All powder samples were stored in desiccators until they were analyzed. One gram of the fine ground sample and 0.5 g of the boric acid were mixed. The mixture was thoroughly grounded and pressed into a pellet of 25 mm diameter using a hydraulic press (20 tons) as per the procedure described earlier.
Energy dispersive X-ray fluorescence technique
The prepared pellets were analyzed using the EDXRF available at Environmental and Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu. The instrument used for this study consists of an EDXRF spectrometer of model EX-6600SDD supplied by Xenemetrix, Israel. The spectrometer is fitted with a side window X-ray tube (370W) that has rhodium as anode. The power specifications of the tube are 3–60 kV and 10–5833 μA. Selection of filters, tube voltage, sample position, and current are fully customizable. The 25 mm 2 silicon drift detector has an energy resolution of 136 eV ± 5 eV at 5.9 keV Mn X-ray, and 10-sample turret enables keeping and analyzing 10 samples at a time. The quantitative analysis is carried out by the inbuilt software nEXT. A standard soil (NIST SRM 2709a) was used as reference material for standardizing the instrument.
| Results and Discussions|| |
Heavy metal distribution in the sediments
The determined heavy metal concentration for 15 coastal locations of east coast of Tamil Nadu by EDXRF is given in [Table 2]. The heavy metal concentration is found to vary from 12.5 to 207.3 mg/kg for Cr; from 1.1 to 19 mg/kg for Co; from 15.2 to 33.63 mg/kg for Ni; from BDL to 3.60 mg/kg for Cu; from 14 to 89 mg/kg for Zn; from 4 to 6.9 mg/kg for As, and from BDL to 35.7 mg/kg for Pb. As can be seen from [Table 2], the mean metal concentrations are in the following order of Cr > Zn > Ni > Pb > Co > As > Cu. The heavy metal concentration of the present study is found to be similar to the results of the other countries in the world., [Figure 2] shows the heavy metal distribution in the sediment of different locations.
|Table 2: Heavy metal concentration (mg/kg) of sediment samples of east coast of Tamil Nadu, India|
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|Figure 2: Heavy metal distribution in the sediment with different locations|
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The total concentrations of heavy metals in sediments do not represent the degree of contamination coming from either natural or anthropogenic sources due to grain-size distribution and mineralogy. Enrichment factor (EF) is a useful tool in determining the degree of anthropogenic impact on sediments. The EF is computed using the following relationship:
In this study, aluminum (Al) was used as the reference element for geochemical normalization because of the following reasons: (1) Al is associated with fine solid surfaces, (2) its geochemistry is similar to that of many trace metals, and (3) its natural concentration tends to be uniform.
Where EF values are <1 background concentration, 1–2 depletion to minimal enrichment, 2–5 moderate enrichment, 5–20 significant enrichment, 20–40 very high enrichment, and >40 extremely high enrichment. EF value of 0.5–1.5 indicates that heavy metal is entirely provided from crustal contribution (e.g., weathering product) in sediment while values >1.5 are considered to indicate an important proportion of noncrustal materials delivered from either natural processes (e.g., biota contributions) or anthropogenic influences.
The EF values of all the sediment samples of the present study area are given in [Table 3]. The EF range of the studied metals was as follows: Cr, 0.922–5.539 (average 3.091); Co, 0.414–2.532 (average 1.264); Ni, 1.145–2.589 (average 1.867); Cu, 0.205; Zn, 0.883–2.261 (average 1.47); As, 1.134–1.798 (average 1.396); and Pb, 0.288–3.815 (average 1.505). The EF values follow the order of Cr > Ni > Pb > Zn > As > Co > Cu.
|Table 3: The enrichment factor values of sediment samples of the present study area|
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The EF values of Cr showed >1.5 in almost sampling locations indicated that Cr was minimal enrichment metal among the studied metals and suggesting that anthropogenic influences. The major source of Cr was shipping and harbor activities, industrial and urban wastage discharges, dredging, etc. The sediment samples at the location of NRB, NVD, SYP, and MTP showed moderately enriched with Co, Ni, Zn, As, and Pb. This indicates that there is a biota contribution or anthropogenic source in addition to the aluminosilicate fraction and also rapid industrialization and urbanization. The variation of EF values of heavy metals along the east coast of Tamil Nadu is shown in [Figure 3].
The contamination factor (CF) was used to express the level of contamination by each metal in the sediment. CF was computed using equation (2):
”Cbackground” refers to the concentration of metal (of interest) in the sediments when there was no anthropogenic input. CF <1 refers to low contamination by a metal, 1 < CF < 3 indicates moderate contamination, 3 < CF < 6 implies considerable contamination, and CF >6 denotes high contamination.
The CF values obtained at all the locations are given in [Table 4]. CF <1 considered as low contamination and was found in the case of Co, Ni, Cu, Zn, As, and Pb mostly at all the locations. Moderate contamination noticed for Cr in the sampling sites of VMP, NVD, NRB, SYP, and PGP. This may be due anthropogenic activities. The anthropogenic activities such as shipping and harbor activities, industrial and urban wastage discharges, dredging, etc., may enhance the metal enrichment. [Figure 4] shows the variation of CF values of heavy metals with locations.
|Table 4: Contamination factor values and pollution load index of sediment samples of east coast of Tamil Nadu, India|
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|Figure 4: The variation of contamination factor and pollution load index with location|
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Possible metal enrichments in aquatic sediments were evaluated using geoaccumulation index (Igeo). The formula used for the calculation of Igeo is expressed as follows:
Where, Cn is the concentration of metal “n” in the sediments, Bn its background concentration, and the factor 1.5 is used because of possible variations of the background data due to lithological variations. The Igeo parameter was successfully calculated using the global average shale data from Turekian and Wedepohl, 1961.
According to the scale established, a sediment can be classified as nonpolluted (Igeo < 1), very slightly polluted (1 < Igeo < 2), slightly polluted (2 < Igeo < 3), moderately polluted (3 < Igeo < 4), highly polluted (4 < Igeo < 5), and very highly polluted (Igeo < 5). The Igeo values for each element at each sampling site were calculated using background values. The calculated Igeo values are based on the world shale average. The Igeo values at all the locations are given in [Table 5].
|Table 5: The geoaccumulation index values of sediment samples of east coast of Tamil Nadu, India|
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The results of Igeo in all the sampling sites were more restrictive, characterizing the sediments as unpolluted with Igeo values <1. This shows that sites are not contaminated by heavy metals. [Figure 5] shows the variation of Igeo values of heavy metals with locations.
Pollution load index
The pollution load index (PLI) provides a simple, comparative means for assessing the level of heavy metal pollution. PLI is determined as the n th root of the product of nCf:
Where Cf is the CF and n is the number of metals. PLI represents the number of times by which the heavy metal concentrations in the sediment exceed the background concentration and gives a summative indication of the overall level of heavy metal toxicity in a particular sample. In general, the PLI is a convenient measure of geochemical trends and is used for comparison among areas. According to Tomlinson et al., 1980, PLI >1 means that pollution is present; if it is below 1, there is no metal pollution. The PLI ranged from 0.238 (Muthialpet-MTP) to 1.000 (Auroville-ARV) [Table 4]. According to the mean PLI value (0.499), the east coast of sediments was practically nonpolluted. [Figure 4] shows the variation in PLI values with locations.
Potential ecological risk by sediment quality guidelines
Sediment quality guidelines (SQGs) can be used to evaluate the degree to which the sediment-associated chemical status might adversely affect aquatic organisms and be designed to aid in the interpretation of sediment quality. These guidelines have been widely used to screen sediment contamination by comparing sediment contaminant concentrations with the corresponding quality guidelines in aquatic ecosystems., This guideline was used correctly classifying sediments as either toxic or nontoxic. SQGs developed for sediments ecosystems., The SQGs, effect range low (ERL)/effect range median (ERM), threshold effect level (TEL), probable effect level (PEL), severe effect level (SEL) were applied in this study, to assess the ecotoxicological sense of heavy metal concentrations in sediment samples. The comparison between SQGs and heavy metals concentration (mg/kg) in the present study in each guideline is given in [Table 6]. The concentration of Ni is greater than TEL and ERL for all the sampling locations but less than the SEL and ERM. Similarly, the concentration of Zn in all the sampling locations is less than the TEL, PEL, ERL, ERM, and SEL.
|Table 6: Comparison between sediment quality guidelines and heavy metals concentration (mg/kg) in the present study with percentage of sample in each guideline|
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The concentration of Cr is greater than TEL and less than the PEL and slightly less than the ERM. These SQGs' results indicate that the concentrations of Cr and Ni are likely to result in harmful effects on sediment-dwelling organisms due to human activities in the coastal area. However, other heavy metals are naturally present in the sediments.
| Conclusion|| |
Sediment pollution in the present study was assessed using EF, CF, Igeo, and PLI. EF was calculated to differentiate the origin of metals between anthropogenic and geogenic sources. The sequence of the EF of the studied metals is Cr > Ni > Pb > Zn > As > Co > Cu. EF analysis indicated that anthropogenic influence on the environment has been significant in the case of Cr, Ni, and Zn while Co, Zn, As, and Pb were at moderate levels. Based on the values of Igeo, the sediments are uncontaminated with respect to Cr, Co, Ni, Cu, Zn, As, and Pb. CF indicated low contamination in the case of Cr, Co, Ni, Cu, Zn, As, and Pb mostly at all the locations. Similar results were also obtained from PLI.
The SQGs indicate that the average concentration of Cr is greater than PEL and ERM while average concentration of Zn is greater than TEL and ERM. This shows that sediment samples are polluted by Cr and Zn. The results of the present investigation and actual knowledge about the metal distribution in this sediment indicate that continuous monitoring and efforts of remediation are required to improve the coastal environment near industrialized areas. The result of this research can be used as the baseline data for the future assessment of some major, minor, and trace elements in sediments along the east coast of Tamil Nadu.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]