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Arabian Journal of Geosciences ISSN 1866-7511 Arab J GeosciDOI 10.1007/s12517-015-1862-z

Elemental distribution in the calcite andaragonite layers of Chione californiensisfrom the Iraqi Coasts—North Arabian Gulf

Moutaz A. Al-Dabbas & Mohanad H. Al-Jaberi

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ORIGINAL PAPER

Elemental distribution in the calcite and aragonite layersof Chione californiensis from the Iraqi Coasts—NorthArabian Gulf

Moutaz A. Al-Dabbas & Mohanad H. Al-Jaberi

Received: 28 November 2014 /Accepted: 24 February 2015# Saudi Society for Geosciences 2015

Abstract The geochemical analysis of Chione californiensisshells is carried out to study the environmental zonal varia-tion in the Iraqi coasts—north Arabian Gulf. Samples ofshells and sea water are collected during low tide periodfrom March to August 2011, from three different stations(Khor Abdullah, Khor Shytianah, and Hacham Island). Thestudied water samples have clearly indicated that chloridegroup are the dominant with one major family (Chloride-sodium family) and one water type which is rNa>rMg>rCa; rCl>SO4. The hydrochemical analysis reflects relative-ly three zones of water salinity namely Khor Abdullah withTDS ranges from 39,215 to 40,100 ppm, Khor Shytianahwith TDS ranges from 44,620 to 45,220 ppm and HachamIsland with TDS ranges from 41,190 to 41,220 ppm. X-raydiffractometry of shells of C. californiensis reveals that theyhave two layers, an inner layer constitutes of aragonite andouter layer constitutes of calcite. The geochemical analysesof the whole shell of C. californiensis reveal positive corre-lation between water salinity, chemical constituents. Excep-tion is found for SiO2, Al2O3, and P2O5 which have nega-tive correlation with water salinity. The chemical constitu-ents of SiO2 %, Al2O3 %, MgO %, Fe2O3 %, Co, Zn, Cr,and Pb show direct relation with the calcite whereas CaO %,P2O5 %, Na2O %, K2O %, Ba, Sr, Rb, and Sr/Ca ratio showdirect relation with the aragonite. The shell of Chionecaliforniensis is found to be a useful tool for monitoringcontamination in the Iraqi marine environments.

Keywords Contamination .Chione californiensis shell .

Chemical constituents . Iraqi coasts

Introduction

The use of marine bivalves as environmental indicators hasreceived considerable attention. Bivalves are believed to in-corporate trace elements into their shells in proportion to theconcentration of those elements in water (Censi et al. 2006).This incorporation is also influenced by other circumstances,including water temperature and salinity (Al-Dabbas et al.1983 and 1984). The incorporation of trace elements into ma-rine bivalves could be used to monitor temporal changes inaspects of the marine environment, including the elementalcomposition of the water (Boening 1999).

Monitoring of chemical components in marine environ-ment (especially in coastal zones) is very important to assessthe contamination in such environment (Babukutty andChacko 1995; Cravo et al. 2004). Traditional monitoring ofheavy metals in the aquatic environment involves determiningand comparing the metal in water, sediment, and biota (Szefer,et al. 2002; Liu and Kueh 2005; Hamed and Emara 2006;Darvish 2007). Many of the previous studies have used theseshells as indicator to the pollution in the coastal areas as theseshells are sensitive to pollutants and hence are considered asgood biomonitoring agents for pollutant and heavy metalmonitoring in aquatic ecosystems (Vlahogianni et al. 2007;Maanan 2008).

The molluscs’ bivalves Chione californiensis are chosen inthis study because of their high distributions in Iraqi shore-lines. Their tolerance and adaptability to frequent periods ofsalinity and temperature changes have made them the pre-ferred organisms for monitoring contaminants and constitute

M. A. Al-Dabbas (*)College of Science, University of Baghdad, Aljaderia,P. O. Box: 47138, Baghdad, Iraqe-mail: profaldabbas@yahoo.com

M. H. Al-JaberiCollege of Science, University of Basra, Basra, Iraqe-mail: jaberi76@yahoo.com

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reliable indicators of the quality of given ecosystems. In addi-tion, C. californiensis shell is bimineralic shell, comprisingcalcite and aragonite allowing investigation of trace elementsin both polymorphs and knowledge the role of the surround-ing water in the concentration of these elements (Al-Jaberi2013).

Iraqi coasts of the northern Arabian Gulf such as KhorAbdullah, Khor Shytianah, and Hacham Island are developingareas (Fig. 1). Water discharge by boats and ships, marinetransportation, ballast water discharges, and industrial dis-charges are main sources of pollutants in these areas. Theseactivities, along the Iraqi coasts have caused the study area tobe exposed to different kinds of pollutants, especially heavymetals. Bivalves especially C. californiensis are widely dis-tributed in this area, and there is a lack of data related to theirheavy metal content.

This research attempts to study the chemical constituents ofthe calcite and aragonite layers in the shells ofC. californiensisand their relations with the sea water chemical and physicalcharacteristics within the Iraqi coasts.

Materials and methods

Three different stations are chosen to study the geochem-istry of C. californiensis’s shells, along Iraqi coasts, fromKhor Abdullah, Khor Shytianah, and Hacham Island

(Fig. 1). Samples of shells and water are collected duringlow tide period from March to August 2011. Four repli-cates of water and shells’ samples are collected from eachsite.

Hydrochemical analyses were carried out to determinethe following: hydrogen number (pH), total dissolvedsolids (TDS), electrical conductivity (EC), and the ma-jor cations (K+, Na+, Ca2+, and Mg 2+) and anions(Cl‾, SO4

2‾, HCO3‾, and CO32‾).

ThirtyC. californiensis shells of the same size (4 to 7 cm)are collected from Khor Abdullah, Khor Shytianah, andHacham Island sampling stations (Fig. 2). Nine complete(non-broken edges)C. californiensis’s shells were chosenand prepared for this investigation.

C. californiensis is classified using Wang and Guo (2008)classifications, as Phylum Mollusca, Class Bivalvia, SubclassHeterodonta, Order Ostreina, Superfamily Veneracea, FamilyVeneridae, Subfamily Chioninae, and Genus C. californiensis.

The shell samples are placed in an acid-washed polyethyl-ene bag. Debris’s are removed from each sample in the labo-ratory. After washing the shells with double distilled water,they were powdered by a glass mortar and were stored inpolyethylene pillboxes. The scanning electron microscope,X-ray diffraction, and ICP analysis were applied (Al- andMohanad 2013).

Fig. 1 Distribution of Chione californensis shells within the sampling site locations

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Two layers, the inner aragonite layer (nacreous layer) andouter calcite layer (prismatic layer), are recognized by X-raydiffraction (CuKq) analysis and SEM; the percentages of theselayers are different from genus to other (Al- andMohanad 2013).

The inner aragonite layer was separated from calcite layerfor nineC. californiensis specimens by using an Electric HandVibrating Hobby tool since it is the only known method forseparation (even that this method may contaminate the sam-ples in the same degree).

Separation has been done and identified for both cal-cite and aragonite layers (Fig. 3). The purity of aragonitewas tested by X-ray diffraction method and about 95 %purity is found to have been attained (Fig. 4). The crys-tals of calcite and aragonite was recognized by SEMmicroscope. Both Figs. 5 and 6 show regular prismaticcalcite and nacreous aragonite in Chione californiensis’sshells. The chemical composition of the calcite and ara-gonite are determined in both carbonate layers. The

Fig. 2 Calcite and aragonitelayers in Chione californiensisshells from the studied sites

Fig. 3 X-ray diffractogram ofcalcite and aragonite minerals inthe Chione Californiensis shell

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geochemistry of C. californiensis’s shells were acquiredfor the following constituents: MgO %, SiO2 %, Al2O3

%, K2O %, Na2O %, Fe2O3 %, P2O5 %, Co, Ni, Rb, Sr,Zn, Cu, Ba, Cr, Pb, and Sr/Ca ratio. These analyses were

executed in both calcite and aragonite layers ofC. californiensis shells. Shells samples from a non-polluted site were collected and analyzed in this studyfor comparison purposes.

Fig. 4 X-ray diffractogram ofaragonite layer in the Chionecaliforniensis shell

Fig. 5 a,b Prismatic calcite crystals for Chione californiensis shell under SEM

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Result and discussion

Hydrochemical analysis

The results show that the TDS inKhorAbdullah, Khor Shytiana,and Hacham Island are 39,215–40,100 ppm, 44,620–45,220 ppm, and 41,190–41,220 ppm, respectively. They are, there-fore, saline water according to Hem (1985) water classification(Table 1). Since, there is positive relationship between electricalconductivity (EC) and total dissolved solids (TDS). Three zoneshave been indicated according to the EC inKhorAbdullah, KhorShytiana, and Hacham Island with EC ranges from 60 to63 mmohs/Cm, 69–71 mmohs/Cm, and 64–65 mmohs/Cm, re-spectively. The hydrogen number (pH) values forKhorAbdullahranges from 7.5 to7.9, Khor Shytianah ranges from 7.7 to 8, andHacham Island ranges from 7.8 to 8.2 (Table 1).

The result of using Schoeller (1972) method to classify thestudied water samples, and identifying their water types haveclearly indicated that chloride group are the dominant withone major family (Chloride-sodium family) and one watertype which is rNa>rMg>rCa: rCl>SO4.

This variation can be attributed to the characterization ofthe marine water or to the spatial variation in controlling

factors that are responsible for sedimentation and dissolutionof different minerals.

Chemical analysis of aragonite and calcite layers

Concentration of trace elements to specific carbonate shelllayers controlled by the relative acceptability of the elementsinto the lattice and the quantity of foreign elements in the shellreflects the concentration of those elements in the surroundingwater (Dodd 1965; Chow et al. 1976; Phillips 1977). Infact,filter feeder, such asC. californiensis, are particularly valuablein water quality investigation, since shell variation developingduring growth should directly reflect the ambient water con-dition (temperature, salinity, dissolved, and suspended load)(Phillips 1977). The ranges of the measured chemical constit-uents (MgO%, SiO2%, Al2O3 %, K2O%, Na2O%, Fe2O3%,and P2O5 %, Co, Ni, Rb, Sr, Zn, Cu, Ba, Cr, Pb, and Sr/Ca) oftheC. californiensis shells at the studied areas in both layers ofaragonite and calcite as well as the mean values and standarddeviation of shell samples from a non-polluted site for com-parison purposes are shown in Table 2.

The results show positive correlation between the chemicalconstituents and sea water salinity with relatively higher

Fig. 6 a,b Nacreous aragonite crystals for Chione californiensis shell under SEM

Table 1 Physical and chemical parameters of the studied sites in the Iraqi coastal marine environment

Sampling site pH EC mmohs/Cm Na+

epmK+

epmCa2+

epmMg2+

epmCl‾epm

SO42‾

epmHCO3‾epm

CO32‾

epmTDSppm

Khor Abdullah 7.9–8.1 60–63 566–578 7.4–8.0 25–28 123–125 651–657 64–66 3.3–3.7 0.3–0.5 39,215–40,100

Khor Shytianah 8–8.2 69–71 657–674 8.1–8.5 30.5–32.5 170–179 766–771 77–80 2.4–2.5 0.7–0.73 44,620–45,220

Hacham Island 7.8–7.9 64–65 606–609 8.1–8.3 28–30 125–131 695–700 72–73 2.5–2.8 0.6–0.7 41,190–41,220

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correlation factor values for most of the studied chemical con-stituents (MgO, Na2O, Fe2O3, Sr, K2O, Cu, Zn, Pb, Cr, Ba,Rb, Ni, and Co) of samples collected fromKhor Shytianah (S)and Hacham Island (H), as compared with those of Khor Ab-dullah (A), in both layers of aragonite and calcite, except forSiO2, Al2O3, and P2O5 percentages, where higher values werefound in Khor Abdullah samples (A) (Tables 1 and 2).

Some elements are concentrated in the calcite outer layermore than in the aragonite inner layer. However, the ratio ofthe elemental distribution in calcite to aragonite layer varieswidely from element to other. The studied chemical constitu-ents have different behaviors; they increase within the calcitelayer such as MgO, SiO2, Al2O3, Fe2O3, Co, Zn, and Pb. Bycontrast, others increase within the aragonite layer such asP2O5 %, K2O %, Na2O %, Ba, Cr, Rb, Sr, and Sr/Ca.

In fact, one major control on trace and minor elements ineither calcite or aragonite is crystallochemical. The calcitestructure accommodates Ca2+ (ionic radius 1.00 Å) as wellas minor and trace elements having an ionic radius less thanor equal to 1.00 Å. The aragonite structure accommodatesCa2+ together withminor and trace elements having radii closeor greater that 1.00 Å (Deer et al. 1992).

The results reflect that Mg, Si, Al, and Zn, which have largeionic radii, are present in higher concentration in the calcitethan in aragonite layer, especially Zn element. Pb element,which also has large ionic radius, is present in higher concen-tration in the calcite layer comparable to the aragonite layer.On other hand, Cr and P elements which have small ionicradii, are present at higher concentrations in aragonite ratherthan calcite.

Sr/Ca values in the aragonite layer are more than that of thecalcite layer. The surroundingwater is the main source for theseelements in the structure of C. californiensis’s shells. Shellcomposition changes as a result of changing water chemistry(Yatabe et al. 2000; Dalbeck 2008). Consequently, the aquaticenvironment had an important role in providing the calcite andaragonite layers by the elements (Tables 1 and 2).

The Sr/Ca ratio can be used for determination of thepaleosalinity and paleotemperature of an ancient environmentas reported by Chilingar et al. (1967); Klein et al. (1996) andThorn et al. (1995). The Sr/Ca value is increase with increase ofwater salinity, so it is higher in the Khor Shytianah and HachamIsland shells in comparison to Khor Abdullah’s shells (Table 2).

The Sr and Na were used as indicators to the aragonite layer,while Mg element is indicator to the calcite layer, and theseresults are clear in the geochemical analysis of the studiedshells, which are in accordance with McMillan et al.(2005)and Dalbeck (2008). Reeder (1983) showed that Mg2+ is ableto substitute for Ca2+ in hexagonal calcite, but not in ortho-rhombic aragonite. Therefore, the decrease of calcium elementin the calcite layer and increase of the magnesium can be at-tributed to higher paleotemperature in the Iraqi shorelines.

Generally, most P, Si, and Al are related to surfacial con-tamination and to interstitial grains of amorphous silica orclays. The factors controlling trace elements concentration inclay are influenced by pH–Eh, drainage, climate, time, clayfraction content, organic matter content, pollution, and otherfactors (Caihuan andWang 2001). However, it is believed thatthe clay content is relatively higher in Khor Abdullah, due tothe influence of sediment transport loads that are carried

Table 2 The geochemical analysis of the aragonite and calcite layers for the Chione californiensis shells of Khor Abdullah (A), Khor Shytianah (S),and Hacham Island (H)

Aragonite Calcite

Elements A S H Mean S.D. Elements A S H Mean S.D.

Al2O3 % 0.066 0.04 0.051 0.053 0.013 Al2O3 % 0.11 0.09 0.087 0.09 0.012

MgO % 0.047 0.049 0.048 0.0475 0.001 MgO % 0.135 0.142 0.14 0.139 0.003

SiO2 % 0.075 0.069 0.07 0.071 0.0032 SiO2 % 0.492 0.473 0.478 0.481 0.009

P2O5% 0.069 0.060 0.062 0.063 0.004 P2O5 % 0.022 0.013 0.018 0.017 0.004

Na2O % 0.63 0.67 0.65 0.648 0.021 Na2O % 0.474 0.562 0.501 0.512 0.04

K2O % 0.1 0.14 0.12 0.118 0.02 K2O % 0.07 0.085 0.08 0.078 0.007

Fe2O3 % 0.15 0.18 0.16 0.163 0.015 Fe2O3 % 0.17 0.20 0.18 0.183 0.015

Ba ppm 13.2 14.1 13.6 13.63 0.45 Ba ppm 10.3 11.5 11.2 11 0.62

Cr ppm 20.1 20.9 20.7 20.56 0.41 Cr ppm 8.7 9.6 9.2 9.16 0.45

Pb ppm 19 24 22 21.6 2.51 Pb ppm 28 32 29 29.6 2.08

Rb ppm 1.18 2.64 1.33 1.71 0.803 Rb ppm 0.53 0.63 0.57 0.57 0.05

Sr ppm 2077 2383 2300 2253 158 Sr ppm 1042 1138 1114 1098 49

Zn ppm 180 211 190 193 15 Zn ppm 218 223 221 220 2.51

Co ppm 0.43 0.95 0.61 0.66 0.26 Co ppm 0.75 1.16 0.89 0.93 0.2

(Sr/Ca)103 5.32 6.05 5.86 5.74 0.37 (Sr/Ca)103 2.69 2.92 2.84 2.81 0.11

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annually by Shatt Al-Arab fresh water river to the sea water,consequently, relatively reducing the sea water salinity, as wellas the ions concentration. Biomonitors’ organisms accumulatethe chemical constituents and heavy metals from ambient bio-available sources of the trace metal over a period (Rainbow2006). TheC. californiensis like other molluscs’ is suspensionfeeder and can uptake the heavy metals from suspended sed-iment (Caihuan and Wang 2001). Thus, the shells ofC. californiensis were found to be useful tool for monitoringcontamination (Shulkin et al. 2003).

The pollution in the Iraqi coasts water may be formed as aresult of the oil spill by the oil carrying ships in the navigationchannel in the north and northwestern parts of the ArabianGulf.

Conclusions

The environmental pollution increased at Khor Abdullah,Khor Shytianah, and Hacham Island during the last fewyears. The main sources of pollutants may be originatedfrom oil spill.The geochemical analysis results show that positive cor-relations are found between water salinity of the samplingsites and the chemical constituents in C. californiensisshells analyzed two layers of calcite and aragonite. Whilenegative correlation is found between water salinity andSiO2, Al2O3 and P2O5. It is believed that the clay contentand fertilizers are relatively higher in Khor Abdullah dueto the influence of Shatt Al-Arab sediments transportloads to the sea water of the Arabian Gulf.The major control on trace and minor elements in eithercalcite or aragonite is crystallochemical, clay content, andthe surrounding water chemistry.The shell of C. californiensis is found to be a useful toolfor monitoring contamination in the Iraqi marineenvironments.

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