A baseline study on trace element based sediment ...

Marine Pollution Bulletin 133 (2018) 117–123

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Baseline

A baseline study on trace element based sediment pollution and potential ecological risk of reef sediments of Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India

T

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P. Saravanana, D. Pradhapa, S. Krishnakumarb, , Judith D. Silvac, A. Vidyasakard, Merin Sackariac, Prince S. Godsone, K. Arumugamb, N.S. Mageshf a

Department of Geology, University of Madras, Guindy campus, Chennai 600 025, India Institute for Ocean Management, Anna University, Chennai 600025, India Department of Energy, University of Madras, Guindy campus, Chennai 600 025, India d Department of Geology, Periyar University PG Extension Centre, Dharmapuri 636701, India e Department of Environmental Sciences, University of Kerala, Kariavattom campus, Thiruvananthapuram 695581, India f Department of Geology, Anna University, Chennai 25, India b c

A R T I C LE I N FO

A B S T R A C T

Keywords: Reef sediments Ecological risk Trace elements Index calculation

The aim of the present study is to assess the baseline level of the trace element, sediment pollution and potential ecological risk of reef associated sediments of Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India. The grain size distribution of the sediments is chiefly controlled by corals and broken shell debris. The distribution of lithoclastic fractions and element concentration are most probably derived from longshore sediment transport and fluvial process from nearby mainland. The enrichment of organic matter is chiefly controlled by mangrove litters and sea grasses. The concentration of lead in the marine sediments is subjected to sediment matrix, vicinity of the local pollutant sources and distance from the mainland coast. The ecological risk assessment clearly reveals that the sediments belong to the low risk category.

Corals are serving as a storehouse of biological diversity and help to protect and stabilize the shoreline. Corals species generally surviving between 28° N and 28° S and well, flourishing under warm water with a temperature range between 20 and 30 °C (Smith, 1978). Clean water with specific salinity and low nutrient content are required to survive the coral species. Out of the total reef area of the world which is approximately 6 × 105 km2, nearly 15% is contributed by the shallow ocean floor with a maximum of 30 m depth range. Reef ecosystem is widely affected by human-induced land-based activities including untreated effluent water discharge, offshore and nearshore mining activities (Anu et al., 2007; Jayaraju et al., 2009). The anthropogenic induced toxic elements are associated with sediments as adsorbed ions, oxides, hydroxides, sulfides, sulfates, carbonates, silicates, phosphates and organometallic compounds (Jenne, 1977). The noxious effect of the various elements in the different biota, including coral species has been well documented (Sathawara et al., 2004; Krishnakumar et al., 2010; Horta-Puga and Carriquiry, 2014; Krishnakumar et al., 2015). In general, trace elements are incorporated into soft tissues of the biota through food ingestion and inhalation. The minor/trace intensity of the elements such as Cr, Zn and Cu is required for physiological functions.

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High exposure of these elements is also toxic to the biota. However, the toxic elements, even in a minor dose can have a negative impact on the ecosystem. Gulf of Mannarregion comprises of 21 coral islands which have been declared as a protected marine national park by the Government of India in 1989. The coral islands are sited nearly 2 to 8 km from the mainland of the southeast coast of Tamil Nadu, India. Among these islands, Vilanguchalli and Poovarasan Patti Island has been 1 m below the mean sea level due to excessive erosion and coral mining in the recent past. Two other islands are not grouped under this category because Pandian and Punnayadi islands have been destroyed for the construction of the new Tuticorin port. The area of Pandian and Punnayadi islands ranges from 0.25 to 130 ha. The aerial extent of the Gulf of Mannar coral islands Marine National Park is 6.23 km2 (including Poovarasan Patti and Vilanguchalli island). The coral islands flourish in mangrove species in the intertidal areas, predominant among them being Rhizophora, Avicennia Sp. The Gulf of Mannar Marine National Park (GOMMNP) is enriched with 147 species of seaweeds and 12 species of seagrass. 106 species from 30 genera of hermatypic and 11 species from 10 genera of ahermatypic coral fauna are

Corresponding author. E-mail addresses: [email protected] (S. Krishnakumar), [email protected] (P.S. Godson).

https://doi.org/10.1016/j.marpolbul.2018.05.024 Received 24 January 2018; Received in revised form 7 May 2018; Accepted 13 May 2018 0025-326X/ © 2018 Published by Elsevier Ltd.


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Fig. 1. Sample location and study area map of Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

(Yang et al., 2012). The dilution factor is finally multiplied by elemental concentration. The concentrations of the selected elements (Fe, Mn, Pb, Zn, Cu, Cr and Ni) are analyzed using Graphite Furnace Atomic Absorption Spectrophotometer (Perkin Elmer Analyst 800). The accuracy of the analysis is cross-matched with analytical standard reference material (SRM MESS-2) and the recoveries are almost equal to that of the certified values (Table 1). The recovery efficiency of the studied elements ranges from 96.2 to 99.57%. The limits of detection of the studied elements are 0.01 μg g−1 for Fe, Zn, Cr, Cu, Ni, 0.02 μg g−1 for Mn and 0.05 μg g−1 for Pb. Statistical analysis and factor extraction are executed using SPSS 21 (SPSS, 2001). The inverse distance weighted (IDW) algorithm is used to spatially interpolate the geochemical data and to estimate the values between measurements. Geospatial analysis is applied to interpret the sediment pollution and potential ecological risk status using ArcGIS 10.2. The spatial distribution of the sand-silt-clay ratio is shown in separate spatial maps (Fig. 2a, b & c). The maximum sand fraction along

reported in the area. Poritidae and Faviidae suborder reef-building corals are dominant in these islands (Krishnakumar, 2011). In recent days, environmental geoscientists and government organizations have realized the necessity of creating trace element based baseline data for ecologically sensitive areas like coral and mangrove environments. Under these circumstances, the elemental distribution in the marine sediments and waters of the coral reef environment and growth bands of massive corals has been reported by earlier researchers (Krishnakumar et al., 2017a; Krishnakumar et al., 2015; Rousan et al., 2016; Chen et al., 2010; Al-Rousan et al., 2007; Wyndham et al., 2004). The aim of the present study is to document the baseline record for elemental concentration in the reef sediments of Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India. The reef surface sediments (38 samples) have been collected from Musal, Manoli and Manoli putti Islands, off the Gulf of Mannar to assess the baseline trace element concentration and its potential ecological risk status (Fig. 1). The average water depth of the sampling site ranges from 3 to 8 m. The surface sediments are collected using manually operated Van Veen grab sampler. Very coarse grains and coral debris are removed from the sediments and packed in duly numbered polyethylene bags. The sediment samples are dried in hot air oven at 80 °C to remove moisture content, and pulverized using auto pulverizer (Fritsch-Pulverisette7 instrument). The carbonate content (CaCO3) and trace element analyses have been carried out as recommended by Loring and Rantala (1992). Organic carbon (OC) determination is done by exothermic heating and oxidation with K2Cr2O7 and concentrated H2SO4. The excess amount of K2Cr2O7 is titrated with 0.5 N ferrous ammonium sulphate solution (Gaudette et al., 1974). 0.5 g of pulverized fine powdered sediment (< 63 μm) is completely digested in a closed Teflon bomb with steel jacket (Techinstro Limited, Pune, India) using aqua regia (2 h at 120 °C; HNO3: HClO4: HF - 3:2:1 ratio). The final digested solution is centrifuged at 200 RPM and diluted to 50 ml

Table 1 Comparison of standard reference material (SRM) MESS 2 certified values for total trace elements. Elements

Fe Cr Mn Ni Cu Zn Cd Pb

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SRM MESS 2 Obtained value

Certified value

% Recovered

4.25 104.1 322.6 45.3 33.2 153 0.23 21.9

4.34 105 324 46.9 33.9 159 0.24 22.3

97.93 99.14 99.57 96.59 97.94 96.23 95.83 98.21


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Fig. 2. Spatial distribution of sand, silt and clay percentage in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

Fig. 3. Spatial distribution of the calcium carbonate (CaCO3) and organic matter (OM) in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

chiefly controlled by the locally available Fe-Mn rich lithoclastic grains. The available heavy mineral grains with sediments also significantly contribute towards the enrichment of iron composition. The typical observation of heavy mineral along the northeastern part of the island is supported for these concluding remarks. The concentration of Cu and Zn indicates the local enrichment with respect to sampling sites and composition of the sediment matrix (Fig. 4a, b, c & d). The copper concentration is less than the UCC mean value. However, nearby coral islands show very low enrichment of this element (Krishnakumar et al., 2017b). The sampling sites show a low concentration of chromium and nickel, except for a few locations. The concentration of lead is found to be lower than the continental crustal average (Taylor, 1964). The possible source for lead concentration in the reef associated marine surface sediments are untreated effluent discharge from industrial areas and coral incinerating power plants. The above conclusion is drawn and reported in various literature by earlier researchers (Magesh et al., 2013; Krishnakumar et al., 2017a; Krishnakumar et al., 2017b). The maximum level of bio-accumulation of Pb and Cd is reported in corals (Acropora and Porites Sp.) and their growth bands (Anu et al., 2009;

the seaward side, particularly in the northeastern part of the study area, is due to the presence of available calcareous sandy materials. According to Krishnakumar et al., 2017b, most of the sand and silt grade fractions are derived from coral and broken shell debris. The distribution of the sand and silt grade fractions in the coral environment is chiefly controlled by the hydrodynamic process, the shape of the coral island and intensity of waves and currents along the coast. The low percentage of the clay fraction may be due to removal/migration of fine clay size fractions towards the considerably deep regions. The distribution of CaCO3 content is partially matched with the distribution of sand grade fraction. The above observation may be due to the presence of lithoclastic grains derived from longshore sediment transport, fluvial followed by the aeolian process. However, the enrichment of organic matter with reef sediments is mostly derived from mangrove litters (Fig. 3a & b). The above conclusion is confirmed by field observation during sample collection along the coast. Further, enrichment of organic matter in the adjacent sampling locations may be due to the vicinity of dense mangrove vegetation along the leeward side of the island. The spatial distribution of Fe and Mn clearly shows that they are 119


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Fig. 4. Spatial distribution of Fe, Mn, Cu and Zn in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

Fig. 5. Spatial distribution of the Ni, Pb and Cr in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

The enrichment factor (EF) of each element is calculated by normalized element (Fe concentration) to compensate for the natural variability of selected elements (Blomqvist et al., 1992).

Krishnakumar et al., 2010; Krishnakumar et al., 2015). The mean concentration of Cd is slightly elevated than the continental crustal average value. The overall observation of trace element distribution suggests that the sediment calcareous matrix significantly controls the element accumulation (Fig. 5a, b, c & d). 120


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Fig. 6. Spatial distribution of the Pollution Load Index (PLI) in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

Fig. 7. Spatial distribution of the Sediment Pollution Load Index (SPI) in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India.

5–10 for moderately severe enrichment, 10–25 for severe enrichment, 25 to 50 for very severe enrichment, and > 50 for extremely severe enrichment. The enrichment factor of the surface sediments suggests that all the elements fall under the background concentration except Pb and a few samples from Cr and Ni. The index of Geo-accumulation (Igeo) is initially proposed by Muller (1969), in order to measure metal contamination in the marine surface sediments. The present concentration of metal is compared to pre-industrial metal concentration. Here, the crustal average value of each element is taken up as a background concentration of the selected element. The Igeo calculation is made by the following equation.

Table 2 Indices and corresponding degrees of potential ecological risk (Hakanson, 1980). Eri value

Grades of ecological risk of single metal

RI value

Grades of potential ecological risk of the environment

Eri < 40 40 ≤ Eri < 80 80 ≤ Eri < 160 160 ≤ Eri < 320 Eri ≥ 320

Low risk Moderate risk Considerable risk High risk Very high risk

RI < 150 150 ≤ RI < 300 300 ≤ RI < 600 RI ≥ 600

Low risk Moderate risk Considerable risk Very high risk

EF =

Igeo = Log 2

(Metal/ Fe )sample (Metal/ Fe )Background

(1)

Cn 1.5 × Bn

(2)

Here, Cn is the concentration of the selected element in the marine sediment, Bn is the background concentration of the same element. The background concentration of every element is taken from mean continental crust data of Taylor (1964). The factor value 1.5 is multiplied by the background concentration to avoid the lithogenic elemental fluctuation in every sample. According to Geo-accumulation index (Igeo) class for elemental pollution, class 0 represents unpolluted; class

The calculated Enrichment Factor (EF) of each element close to 1 is probably considered as crustal sources/natural origin of the sediments. The classification for element enrichment factor is classified and considered as follows: from 0 to 1 for background concentration or no enrichment, 1–3 for minor enrichment, 3–5 for moderate enrichment, 121


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Fig. 8. Spatial distribution of the Potential Ecological Risk Index (PERI) in Musal, Manoli and Manoli putti Islands, Gulf of Mannar, India. Table 3 Bivariate Pearson correlations for elemental concentration in surface sediments. Parameters

Sand

Silt

Clay

CaCO3

OM

Fe

Mn

Cu

Zn

Ni

Pb

Cr

Cd

Sand Silt Clay CaCO3 OM Fe Mn Cu Zn Ni Pb Cr Cd

1 −0.999a 0.203 −0.161 −0.407b −0.019 −0.011 −0.225 −0.131 −0.007 −0.039 −0.257 −0.329b

1 −0.235 0.149 0.404b 0.022 0.013 0.228 0.127 0.008 0.034 0.251 0.321b

1 0.339b 0.003 −0.099 −0.085 −0.155 0.104 −0.035 0.160 0.126 0.165

1 0.374b −0.338b −0.203 0.087 0.084 −0.048 0.221 0.023 0.202

1 −0.230 −0.267 0.180 −0.031 −0.174 0.084 0.021 0.221

1 0.470a 0.387b 0.303 0.574a 0.131 0.303 −0.007

1 −0.122 −0.082 0.105 0.035 0.226 −0.258

1 0.581a 0.767a 0.175 0.141 −0.018

1 0.753a 0.304 0.555a 0.097

1 0.092 0.452a −0.046

1 0.238 0.260

1 0.380b

1

a b

Correlation is significant at the 0.01 level (2-tailed). Correlation is significant at the 0.05 level (2-tailed).

fall under the unpolluted class. The Pollution Load Index (PLI) compares the concentration of a selected element with the one expected when excluding anthropogenic contributions. The Contamination Factor (CF) is calculated before assessing the pollution load index of the selected samples. The Contamination Factor (CF) and Pollution Load Index (PLI) are calculated by the following equations.

Table 4 Extracted factor loadings using principal component analysis. Parameters

Sand Silt Clay CaCO3 OM Fe Mn Cu Zn Ni Pb Cr Cd

Component 1

2

3

−0.525 0.522 −0.048 0.120 0.182 0.520 0.085 0.730 0.784 0.764 0.360 0.670 0.326

0.642 −0.635 −0.057 −0.522 −0.692 0.571 0.425 0.147 0.225 0.505 −0.069 0.052 −0.485

0.484 −0.505 0.715 0.511 0.020 −0.243 −0.399 0.022 0.312 0.110 0.415 0.118 0.225

CF =

Cmetal Cbackground

PLI = (CF1 × CF2 × CF3 × …….×CFn )1/n

(3) (4)

The Contamination Factor (CF) of each element is determined with respect to the background value in the sediment, where, Cmetal is element concentration in each sample, Cbackground is the background element concentration. The background elemental concentration is taken from the mean continental crust of corresponding elements. Here, CF < 1 - low contamination, 1 ≤ CF < 3 - moderate contamination, 3 ≤ CF ≤ 6 - considerable contamination and CF > 6 - very high contamination (Tomlinson et al., 1980). All the samples fall under the contaminated category except Pb. Nearly 68.5% of the samples are found under considerable contamination, 21% of the samples are grouped under very high contamination and 10.5% of the samples fall under the moderate contamination category of Pb. According to Pollution Load Index (PLI), all the samples fall under the unpolluted

Extraction method: principal component analysis.

0 to 1 represents unpolluted to moderately polluted; class 1 to 2 represents moderately polluted; class 2 to 3 represents moderately polluted to strongly polluted; class 3 to 4 represents strongly polluted; class 4 to 5 represents strongly polluted to extremely polluted and class > 5 represents extremely polluted. The surface sediments of the reef environment are moderate to strongly polluted by Pb. The other elements 122


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2017/000030 & 14th Nov 2017). The authors thank Dr. J. Elizabeth Christina, Assistant Professor, Scott Christian College, Nagercoil, Tamil Nadu, India, for helping in the proof correction.

category (Fig. 6). The Sediment Pollution Index (SPI) calculation has been proposed by Singh et al. (2002) to address the pollution level of the sediments. The application of SPI is helpful to estimate the level of pollution under natural environment.

SPI =

∑ (EFm × Wm)/ ∑ Wm

EFm = Cn/ Cr

References

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The sediment pollution index (SPI) class is classified as five different pollution groups. Here, class 0 to 2 represents natural sediment, class 2 to 5 represents low polluted sediment, class 5 to 10 represents moderately polluted sediment, class 10 to 20 represents highly polluted sediment and class > 20 represents dangerous sediment. The SPI of the sediments reveal that all the samples are under low polluted sediment class (Fig. 7). The potential ecological risk index (PERI) of the ecosystem is assessed through Ecological Risk Factor (ER). The elemental concentration based ecological risk factor for sensitive ecosystem is proposed by Hakanson, 1980. The PERI is studied using the following equation. i Cfi = CD CBi

(7)

Eri

(8)

=

RI =

Tri

× m

Cfi

∑i =1

Eri

(9)

Here, risk index (RI) represents the total of the potential risk of specific elements, Eri is the potential risk of selected elements, Tri is the toxic-response factor for an each selected element, Cfi represent contamination factor, CDi represents the current element concentration in sediments, and CBi is the background concentration of the element in sediments. The toxic response factor for the studied element is shown as below: 5 for Cu, 2 for Cr, 1 for Zn and Mn, 5 for Pb and Ni. The background data (crustal average) is taken up from mean continental crust value (Taylor, 1964). Hakanson recommends five groups of ecological risk index (Eri) and four groups of RI (Table 2). The ecological risk grade (Eri) suggests that the elements fall under the low-risk category (Fig. 8). The bivariate Pearson correlation matrix of the studied parameters explains the relationship between each variable. Fe vs Mn, Fe vs Ni, Cu vs Zn, Cu vs Ni, Zn vs Ni, Zn vs Cr and Ni vs Cr having 0.01 levels of significant correlation between the above-specified parameters (Table 3). The significant relationship between the parameters indicates that the distribution of Fe and Mn is chiefly controlled by the riverine input from the mainland. The distribution of ferromagnesian counterparts like Cr and Ni, Zn and Cu distribution in the surface sediments is mostly controlled by longshore sediment transport. Silt, Fe, Cu, Zn, Ni and Cr show positive factor loadings in factor 1 (Table 4). The factor 1 clearly suggests that the sediments chiefly consist of silt-size sediments. Sand, Fe and Ni have positive factor loadings in factor 2. The riverine controlled distribution of Fe, Mn and trace element confirms the above conclusion. Clay and CaCO3 have positive factor loadings in factor 3. The factor 3 suggests that the clay-size sediment fraction chiefly consists of calcareous sediments, and that the primary source of the calcareous matter comes from coral debris and broken shell fragments. Acknowledgement The corresponding author is thankful to the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), New Delhi for providing financial support through National Post-Doctoral Fellowship Scheme (Ref. No. DST Ref. No PDF/

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