Open Access

A new bioindicator, shell of Trachycardium lacunosum, and sediment samples to monitors metals (Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu) in marine environment: The Persian Gulf as a case

  • Vahid Noroozi Karbasdehi1,
  • Sina Dobaradaran1, 2, 3Email author,
  • Iraj Nabipour4,
  • Afshin Ostovar4,
  • Amir Vazirizadeh5,
  • Masoumeh Ravanipour1,
  • Shahrokh Nazmara6,
  • Mozhgan Keshtkar1,
  • Roghayeh Mirahmadi1 and
  • Mohsen Noorinezhad7
Journal of Environmental Health Science and Engineering201614:16

DOI: 10.1186/s40201-016-0260-0

Received: 11 May 2016

Accepted: 5 October 2016

Published: 10 October 2016

Abstract

Background

The present work was designed to detect heavy metal contents of Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu in sediments and shells of the Trachycardium lacunosum collected in polluted and unpolluted areas along the Persian Gulf.

Methods

The samples were taken from surface sediments (0-10 cm) and shells of Trachycardium lacunosum in two separated areas (polluted and unpolluted) in northern part of the Persian Gulf, Asaluyeh Bay, during summer 2013. The prepared samples were analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES).

Results

Based on the results, all measured metals including Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu were meaningfully higher in the sediment samples of polluted area compared to unpolluted area and the order of metal concentrations in the sediment samples were Cr > Co > V > Ni > Zn > Cu > Fe > Al > Mn in polluted area. In the case of shell samples of Trachycardium lacunosum, polluted area contained significantly higher contents of Al, Zn, Fe, Mn, Ni, Co, Cr and Cu compared to unpolluted area and the order of metal concentrations in the shell samples were Fe > Zn > Al > Mn > Cu > Cr > Ni > Co in the polluted area.

Conclusion

It was concluded that shells of the Trachycardium lacunosum can be used as a suitable bioindicator for heavy metals in the aquatic environment. Results confirmed that due to the possible contaminations by oil and gas activities near the polluted area perennial monitoring and mitigation measures is extremely necessary.

Keywords

Aquatic Organisms Environmental Monitoring Geologic Sediments Metals Persian Gulf Trachycardium lacunosum Toxicology

Background

Environment protection needs awareness of the circumstance of the environments and the way in which they change. Hence, deterioration due to human and industrial activities and change in environments are the principal topics of monitoring studies [1]. The data attained in monitoring studies may use as a basic for managers and policy makers for evaluation and enhancement of environment condition by imposing proper actions to protect the environment. Coastline areas are subject to suffer from different negative environmental impacts due to industrial and human activities. Chemical pollution associated with industrial production is the main concern in the marine environment [2]. Heavy metals are considered as one of the most critical contaminants in the marine environment due to their bioaccumulation and biomagnification throughout the trophic chain [3, 4]. Heavy metals toxicity in marine organisms, long residence time within trophic chains, as well as the probable risk of human exposure to heavy metals, makes it essential to evaluate the concentrations of them in the aquatic environment and organisms [5]. Heavy metals may also induce sublethal effect in marine organisms, such as disruption of homeostasis, and impairment at cellular and molecular levels [6]. Additionally, these impacts may seriously decrease the persistence capacity of the organism by enhancing susceptibility to diseases and impairment [7]. Sediments act as a reservoir for various pollutants such as heavy metals and while many bivalves existing inside sediment accumulate elevated concentration levels of metals with regard to their bioaccessibility [8]. The ecological significance of bivalves, their simplicity of applying, their vast distribution and numerous abundance, and their relative to polluted sediments make them suitable species for toxicity testing of sediment [9]. Metals accumulate differentially in the shells and soft tissues of bivalves [10] however there is no particular position on if the use of shells or soft tissues alone is preferred in evaluating of metal [11]. But soft tissues have received further consideration amongst researchists for metals monitoring mostly because of agreement with the US coastal mussel watch monitoring scheme [12]. However, shell can provide a more precise symptom of pollution and environmental change [13]; they give minor variation than the living organism’s tissue also present a historic record of metal level all over the organism’s life cycle. This record still preserved after organism death [14]. High levels of different metals in sediments and organisms of marine environment are a well-documented environment concern [15]. But there are a few comprehensive studies in the Persian Gulf region especially on evaluation of metal contents in the bivalve shells of Trachycardium lacunosum with its connection to metal contents in the sediments. Trachycardium lacunosum is a marine and infaunal bivalve as well as a filter feeder pelecypod that belongs to the Cardiidae family. This bivalve has a white-rimmed shell, with the characteristic pink, brown, and purple spots overt. The average Trachycardium lacunosum length is about 25–35 mm. Trachycardium lacunosum is native to intertidal zone and sandy substrates of the Persian Gulf [16]. Due to the high dispersion of this bivalve in Nayband Bay and Lavar-e-Saheli, in this study we used Trachycardium lacunosum to evaluate its efficiency as a suitable bioindicator for metals.

The Persian Gulf is one of the oldest sea passageways in the world, and nearly 45 % of natural gas and 57–66 % of known oil reserves of the world lie in the region of the Persian Gulf. The presence of large amounts of natural gas and oil has made the Persian Gulf as one of the most strategic waterway in the world. The Persian Gulf has been the main waterway for oil transport in the last decades and during our time has also suffered from repeated oil spills to its marine environment.

To the best of our knowledge there is no report on the concentrations of heavy metals in the shells of Trachycardium lacunosum also there is no detailed study on heavy metal contents in the northern part of the Persian Gulf. So in this study for the first time in the offshore South Pars, the northern part of the Persian Gulf, we aimed to (1) measure the contents of Al, Zn, Fe, Mn, Ni, V, Co, Cr, as well as Cu in the shells of Trachycardium lacunosum and sediments simultaneously in two separated areas (polluted and unpolluted) (2) comparison between the metal contents of sediments in the polluted and unpolluted areas as well as shells (3) determine the interrelationships between metal contents in the shells of Tracycardium lacunosum as well as the sediments in both polluted and unpolluted areas.

Methods

Study area description

The South Pars/North Dome is the world’s biggest gas field, shared between Iran and Qatar, and situated in the Persian Gulf. This natural gas field covers a space of 9700 km2 and the name of this field in Iranian territorial is South Pars. Closest land point to this gas field in the northern part of the Persian Gulf is Asaluyeh. It was chosen as the site for all facilities related to this gas field in Iranian territorial. Asaluyeh is situated on the shore of the Persian Gulf in southeast of Bushehr province. Two different areas were selected in the Asaluyeh as sampling points including polluted area (Nayband Bay) and unpolluted area (Lavar-e-Saheli) (Fig. 1 and Table 1). The surface sediment textures of both polluted and unpolluted areas are silt-clay.
Fig. 1

The map and locations of sampling stations in the study areas

Table 1

Geographical coordinates of the stations studied

Stations of unpolluted area

Number

E

1

28°13'45.59"N

51°17'12.51"E

2

28°13'42.77"N

51°17'13.12"E

3

28°13'40.38"N

51°17'13.37"E

4

28°13'38.14"N

51°17'13.72"E

5

28°13'36.13"N

51°17'13.94"E

6

28°13'34.10"N

51°17'14.12"E

7

28°13'33.77"N

51°17'14.45"E

8

28°13'32.27"N

51°17'14.67"E

9

28°13'30.01"N

51°17'15.02"E

10

28°13'27.49"N

51°17'15.31"E

11

28°13'24.97"N

51°17'15.76"E

12

28°13'22.36"N

51°17'16.18"E

13

28°13'19.04"N

51°17'16.46"E

14

28°13'16.31"N

51°17'17.74"E

15

28°13'14.09"N

51°17'17.81"E

16

28°13'12.08"N

51°17'17.68"E

17

28°13'5.35" N

51°17'17.71"E

18

28°13'2.74" N

51°17'17.86"E

19

28°12'59.71"N

51°17'17.64"E

Stations of polluted area

Number

E

20

27°26'39.57"N

52°40'32.36"E

21

27°26'21.06"N

52°40'34.43"E

22

27°26'2.91" N

52°40'36.37"E

23

27°25'48.69"N

52°40'35.29"E

24

27°25'33.86"N

52°40'35.21"E

25

27°25'21.54"N

52°40'33.93"E

26

27°25'11.54"N

52°40'32.18"E

27

27°25'1.77" N

52°40'29.43"E

28

27°24'52.85"N

52°40'25.78"E

29

27°24'45.36"N

52°40'22.32"E

30

27°24'36.78"N

52°40'18.48"E

31

27°24'27.10"N

52°40'14.73"E

32

27°24'19.29"N

52°40'9.73" E

33

27°24'11.30"N

52°40'5.49" E

34

27°24'4.09" N

52°40'0.34" E

35

27°23'57.01"N

52°39'52.23"E

36

27°23'50.64"N

52°39'41.26"E

37

27°23'49.45"N

52°39'4.93" E

38

27°23'46.16"N

52°39'15.78"E

39

27°23'43.78"N

52°39'27.46"E

Sample collection

Composite samplings based on area (3 different locations for each sample) were performed at low tide times from the tidal area along the Persian Gulf coastal. Samples were collected from surface sediments (0-10 cm) and shells of Trachycardium lacunosum in both polluted and unpolluted areas during summer 2013 as fallow:
  1. a)

    In polluted area: 20 sediment samples and 18 shell samples

     
  2. b)

    In unpolluted area: 19 sediment samples and 13 shell samples

     

After transporting the collected surface sediments to the laboratory, the samples were dried at 105 °C for 24 h, homogenized, and packed in polyethylene bags and kept at -20 °C before analysis. The shell samples washed under a jet of water to liminate algae, sand, clay as well as other impurities, and then dried at 105 °C for 24 h and kept at -20 °C before analysis.

Reagents

All the employed oxidants and mineral acids (HNO3, H2O2, HF, and HCl) were of suprapure quality (Merck, Germany). All plastic and glassware were cleaned by drenching overnight in a 10 % (w/v) HNO3 solution and afterward washed with deionized water before use. All solutions were prepared by ultrapure water (18.2 MΩ cm).

Digestion and analytical procedures

The sediment samples (0.5 g) were digested with 6 ml hydrochloric acid (37 %), 2 ml nitric acid (65 %) in a microwave digestion system for 30 min and then diluted to 25 ml with ultrapure water and stored in polyethylene bottle until analysis. 0.5 g of powdered shell was fully digested in a Teflon cup using a mixture of conc. HNO3, HClO4 and HF with the ratio 3:2:1 respectively. Acids were added to dried sample and left overnight prior to further process. After that the samples were heated at 200°C then left to cool and filtered. The filtered solution was justified to a volume of 25 ml. It should be noted here that shell samples with similar shell length were selected for analysis in each sample point to minimize effects of body weight [17]. The bivalve length was measured by using a caliper with an accuracy of 0.02 mm. Blank digest was similarly performed. Metals analysis of Al, Zn, Fe, Mn, Ni, V, Co, Cr as well as Cu was performed by inductively coupled plasma optical spectrometry (ICP-OES). In Table 2, specifications of the instrumental operating circumstances are shown. All metal levels were represented as μg g−1 dry wet (dw). Statistical analysis of data was performed with the SPSS, Version 21 and Mann-Whitney U test as well as the Spearman’s rho correlation coefficient were used for statistical significant differences. Differences in mean values were accepted as being significant if P < 0.05.
Table 2

ICP-OES instrumental operating details

Parameters

 

Company, model

SPECTRO (Germany), Spectro arcos

RF generator power (W)

1400

Frequency of RF generator (MHz)

27.12 MHz

Type of detector

Charge coupled devices (CCD)

Torch type

Flared-end EOP torch 2.5 mm

Plasma, auxiliary, and nebulizer gas

High purity (99.99 %) argon

Plasma gas flow rate (l/min)

14.5

Auxiliary gas flow rate (l/min)

0.9

Nebulizer gas flow rate (l/min)

0.85

Sample uptake time (s)

240 total

Delay time of (s)

-

Rinse time of (s)

45

Initial stabilization time (s)

Preflush: 45

Time between replicate analysis (s)

-

Measurement replicate

3

Pump rate

30 RPM

Element (λ/nm)

Al 396.152; Cu 324.754; Fe 259.941

Mn 257.611; Ni 231.604; Zn 268.416

Cr 205.618; Co 228.616; V 292.402

Result and discussion

Content of metals in sediments and shells

The concentration levels of examined metals (Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu) in sediment samples of polluted (Nayband Bay) and unpolluted (Lavar-e-Saheli) areas are shown in Table 3.
Table 3

Concentration of heavy metals (μg g−1 dw) in sediment samples at polluted & unpolluted areas

Area

Station

Al

Zn

Fe

Mn

Ni

V

Co

Cr

Cu

 

1

0.136

5.4

0.162

0.006

2.1

6.1

16

1.5

2.2

 

2

0.160

5.7

0.176

0.007

2

4.4

25

7.3

4.3

 

3

0.201

6

0.273

0.010

3.1

8.8

22

64.9

1.2

 

4

0.208

5.2

0.224

0.009

4.2

7.1

23

1.3

2.5

 

5

0.251

6.2

0.278

0.010

3.7

7

22

3.5

2

 

6

0.336

6

0.302

0.012

2.8

9.8

22

12.6

0.9

 

7

0.526

6.1

0.411

0.018

6.4

4.4

22

70.7

0.1

 

8

0.704

7.9

0.482

0.024

7.8

6.4

25

1.5

2.6

 

9

0.811

9.2

0.461

0.023

9.4

6.1

22

58.6

2.3

Unpolluted area

10

0.799

8.7

0.445

0.023

8.1

13.4

23

74.7

3.8

 

11

0.466

6.4

0.340

0.016

2.1

10.1

24

2.4

3.7

 

12

0.109

3.2

0.095

0.005

2.2

7

25

1.5

1.9

 

13

0.141

4.4

0.150

0.006

2.6

5.4

23

1

4.5

 

14

0.074

4.7

0.065

0.004

2.2

4.1

25

1.5

3.3

 

15

0.171

7.3

0.129

0.005

4.7

6.8

21

1.3

1.3

 

16

0.145

4.6

0.169

0.007

2.1

4.1

24

6.3

2.1

 

17

0.199

3.9

0.201

0.001

2.1

8

23

1.5

3.9

 

18

0.144

3.8

0.170

0.007

2.2

2.8

23

1.3

2.7

 

19

0.129

4.3

0.139

0.006

2.2

3.1

24

1.4

1.6

Mean ± SD

 

0.3005 ± 0.24

5.737 ± 1.65

0.246 ± 0.13

0.01 ± .006

3.79 ± 2.38

6.574 ± 2.66

22.85 ± 2.06

16.57 ± 27.1

2.47 ± 1.2

 

20

0.161

5.4

0.171

0.007

5.9

5.6

29

170

1.9

 

21

1.543

13.5

1.256

0.051

19.3

23.6

22

148.3

4.1

 

22

1.488

15.6

1.532

0.053

19.4

27.2

26

438.3

1.6

 

23

1.233

10.6

1.183

0.051

16

23.1

27

103.9

3.3

 

24

1.108

10.3

1.150

0.049

17.4

21.7

21

93.8

8.3

 

25

0.903

8.6

1.066

0.049

14.8

17

34

102.3

2.6

 

26

0.928

10.1

1.067

0.048

16.9

21.6

35

92.3

1.8

 

27

0.648

9.2

0.939

0.049

15.3

17.4

45

49.4

2.2

 

28

0.831

9.6

0.997

0.048

15.3

13.3

24

48.9

4.2

Polluted area

29

0.988

11.1

1.188

0.050

16.4

19.1

34

71.5

3.8

 

30

0.986

9.6

1.205

0.051

17

21.7

160

68.7

4.5

 

31

1.167

11.5

1.243

0.049

18.4

26.4

21

96.1

2.5

 

32

1.374

12

1.333

0.052

20.7

27

25

147.1

3.5

 

33

0.843

9.9

1.144

0.048

16.4

13.4

25

53.6

2.9

 

34

0.778

9.1

1.083

0.047

16.2

17.9

26

41.3

5.1

 

35

0.712

11.2

1.016

0.049

13.6

19.4

35

44.9

2.7

 

36

1.046

10.7

1.230

0.051

17.8

15.1

27

97

4

 

37

0.955

11.2

1.211

0.054

14.8

23.5

22

76.6

3.1

 

38

0.784

9.9

1.097

0.050

15.3

19.9

23

74.2

2.8

 

39

0.739

8.2

1.051

0.048

16.2

13.7

25

65

2.7

Mean ± SD

 

0.960 ± 0.315

10.37 ± 2.05

1.108 ± 0.26

0.048 ± 0.009

15.490 ± 2.3

19.38 ± 5.4

34.3 ± 30.2

104.16 ± 86.4

3.38 ± 1.5

The orders of metal concentration levels in the sediment samples were Cr > Co > V > Ni > Zn > Cu > Fe > Al > Mn in the polluted area (Nayband Bay) and Co > Cr > V > Zn > Ni > Cu > Al > Fe > Mn in the unpolluted area (Lavar-e-Saheli).

In the unpolluted area the contents of Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu ranged from 0.074–0.811 (Mean: 0.3005), 3.2–9.2 (Mean: 5.737), 0.065–0.482 (Mean: 0.246), 0.004–0.024 (Mean: 0.01), 2–9.4 (Mean: 3.79), 2.8–13.4 (Mean: 6.57), 16-25 (Mean: 22.85), 1–74.7 (Mean: 16.57), and 0.1–4.5 (Mean: 2.47) μg g−1 respectively. In the polluted area the contents of Al, Zn, Fe, Mn, Ni, V, Co, Cr as well as Cu in the sediment samples ranged from 0.161–1.543 (Mean: 0.960), 5.4–15.6 (Mean: 10.37), 0.171–1.532 (Mean: 1.108), 0.007–0.054 (Mean: 0.048), 5.9-20.7 (Mean: 15.490), 5.6–27.2 (Mean: 19.38), 21–160 (Mean: 34.3), 41.3–438.3 (Mean:104.16), and 1.6–8.3 (Mean: 3.38) μg g−1 respectively. Ismail and Safahieh measured the content levels of Cu and Zn in the sediment samples collected from intertidal areas in the Lukut River. They have reported that Cu and Zn in the surface sediments were within the range of 37 to 100 μg g−1 and 100 to 210 μg g−1 respectively [18]. According to Usero et al. report, the concentrations of Cr, Cu, Pb, Zn, As and Hg in the sediments of Atlantic coast in southern Spain ranged from 10–33, 3–13, 0.26–0.72, 2–46, 18–460, 3.5–102 and 0.11-0.41 mg kg−1 dry mass respectively [19]. In another study, Palpandi and Kesavan measured concentration levels of heavy metals including Zn, Mn, Cu, Al, Cr and Ni in the sediment samples of Velar estuary, Southeast coast of India. They reported that the mean concentration levels of Cu, Fe and Zn ranged from 39.28 ± 0.6, 178.28 ± 1.12, 16.28 ± 1.24, 542.00 ± 487.58, 9.44 ± 3.11 and 1.64 ± 1.20 μg g−1 respectively [20].

Statistical analysis of Mann-Whitney U test showed that sediment samples in the polluted area contained significantly higher concentrations (P < 0.05) of all measured metals (Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu) compared to unpolluted area (Table 4). The comparison between metal concentrations in polluted and unpolluted areas are shown in Fig. 2.
Table 4

The differences between the metal concentrations of samples in polluted and unpolluted areas

Heavy metals

P-value sediments

P-value shells

Al

0.000

0.006

Co

0.009

0.000

Cr

0.000

0.000

Cu

0.021

0.001

Fe

0.000

0.000

Mn

0.000

0.000

Ni

0.000

0.009

V

0.000

-

Zn

0.000

0.000

Fig. 2

Comparison of heavy metal concentration levels in the sediment samples at polluted and unpolluted areas

Sediments act as both sinks and carriers for pollutants in the marine environments. Heavy metals are among the most usual marine contaminants and their occurrence in the marine environment indicates the presence of natural or anthropogenic source. Many studies have illustrated that heavy metal concentration in sediments can be sensitive indicators of pollutants in the marine environment [21, 22]. High concentration levels of trace metals in marine environments due to human activities have been recorded since old times. But elevated releases of toxic metals in to the municipal areas and the related health consequences just become clear in the 1960s [23]. Our study showed higher contents of Al, Zn, Fe, Mn, Ni, V, Co, Cr, as well as Cu in the Nayband Bay (polluted area) compare to unpolluted area mainly due to the activities of all related industries to gas and oil field in the region, boat repairing platform, shipping activities and discharge of effluents from the domestic sources nearby. The activities of industries after a while can release a diversity of poisonous sand possibly poisonous contaminants into the environment [24]. In a recent study in Jade Bay in NW Germany, the trace metal pollution in surface sediment and suspended particulate substance was described. Various metals including As, Cd, Cu, Ni, Pb, Sn and Zn were increased in the surface sediments. The potential metal sources in the region were the harbor area, floodgates and dumped harbor sludge in different parts of the region [25]. In a study in the Montenegrin coastal area, the overall trend for the concentration levels of measured metals in sediment samples was Fe > Mn > Cr > Ni > Zn > Cu > Co. The result of this study showed the anthropogenic impacts on the metal concentration levels in the Montenegrin beach zone [26]. In another study at Vellar estuary, Southeast coast of India the order of metal accumulation was Fe > Al > Mg > Mn > Cd > Cu > Cr > Zn > Ni > Pb. It was reported that higher level of metals could be due to effluents from municipal, domestic and agricultural wastes [20]. The contents of Al, Zn, Fe, Mn, Ni, V, Co, Cr as well as Cu in the shell samples of Trachycardium lacunosum in polluted (Nayband Bay) and unpolluted (Lavar-e-Saheli) areas are given in Table 5.
Table 5

Concentration of heavy metals (μg g−1 dw) in the shell samples at polluted and unpolluted areas

Area

Station

Al

Zn

Fe

Mn

Ni

Co

Cr

Cu

 

1

0.360

0.465

0.935

0.106

0.003

0.012

0.001

0.061

 

2

0.409

0.528

0.809

0.155

0.005

0.012

0.001

0.043

 

3

0.081

0.003

1.564

0.220

0.007

0.010

0.001

0.004

 

4

0.586

0.756

0.526

0.070

0.020

0.015

0.001

0.043

 

5

0.699

0.404

1.265

0.176

0.006

0.003

0.001

0.003

 

12

0.682

0.274

1.307

0.242

0.005

0.000

0.001

0.008

Unpolluted area

13

0.516

0.666

1.102

0.140

0.002

0.015

0.001

0.003

 

14

0.000

0.179

1.295

0.219

0.003

0.000

0.001

0.010

 

15

0.257

0.332

0.942

0.176

0.003

0.004

0.001

0.009

 

16

0.463

0.598

1.294

0.226

0.007

0.013

0.001

0.014

 

17

0.180

0.232

0.694

0.179

0.003

0.015

0.001

0.003

 

18

0.758

0.104

0.802

0.186

0.005

0.006

0.001

0.003

 

19

0.314

0.405

0.838

0.199

0.003

0.013

0.001

0.003

Mean ± SD

 

0.408 ± 0.24

0.3805 ± 0.22

1.029 ± 0.3

0.176 ± 0.05

0.006 ± 0.004

0.009 ± 0.006

0.001 ± 0

0.016 ± 0.02

 

20

0.260

0.335

0.645

0.234

0.003

0.013

0.001

0.003

 

22

0.727

0.938

4.514

0.980

0.008

0.020

0.057

0.028

 

23

0.624

0.805

2.415

0.743

0.005

0.015

0.019

0.049

 

24

0.641

0.827

3.024

1.022

0.007

0.016

0.055

0.116

 

25

0.213

0.880

1.623

0.299

0.021

0.013

0.118

0.303

 

26

0.139

0.902

1.868

0.388

0.003

0.017

0.083

0.930

 

27

0.678

0.977

3.208

0.285

0.227

0.019

0.071

0.484

 

28

0.640

0.826

2.340

0.645

0.121

0.016

0.001

0.006

Polluted area

29

0.557

0.719

3.265

0.673

0.055

0.012

0.001

0.014

 

31

0.608

0.784

1.998

0.550

0.020

0.015

0.146

0.046

 

32

1.114

1.437

6.850

1.269

0.055

0.022

0.068

0.141

 

33

1.249

1.611

1.911

0.264

0.076

0.014

0.104

0.600

 

34

1.722

2.221

6.126

0.630

0.065

0.015

0.001

0.003

 

35

5.360

6.915

1.828

0.416

0.003

0.013

0.013

0.003

 

36

0.956

1.233

3.747

0.800

0.003

0.017

0.048

0.036

 

37

1.335

1.722

2.333

0.375

0.225

0.017

0.157

0.339

 

38

0.699

0.875

6.543

0.246

0.003

0.019

0.162

0.349

 

39

0.383

0.901

2.790

0.350

0.234

0.015

0.242

1.677

Mean ± SD

 

0.995 ± 1.16

1.385 ± 1.45

3.170 ± 1.76

0.565 ± 0.3

0.063 ± 0.083

0.016 ± 0.002

0.075 ± 0.07

0.285 ± 0.43

The orders of metal concentration levels in shell samples were Fe > Zn > Al > Mn > Cu > Cr > Ni > Co in the polluted area (Nayband Bay) and Fe > Al > Zn > Mn > Cu > Co > Ni > Cr in the unpolluted area (Lavar-e-Saheli). In the polluted area the contents of Al, Zn, Fe, Mn, Ni, Co, Cr, and Cu in the shell samples ranged from 0.139–5.36 (Mean: 0.995), 0.335–6.915 (Mean: 1.385), 0.645–6.85 (Mean: 3.170), 0.234–1.269 (Mean: 0.565), 0.003–0.234 (Mean: 0.063), 0.012–0.022 (Mean: 0.016), 0.001–0.242 (Mean: 0.075), and 0.003-1.677 (Mean: 0.285) μg g−1 respectively. In the unpolluted area the concentration levels of Al, Zn, Fe, Mn, Ni, Co, Cr, and Cu ranged from 0–0.758 (Mean: 0.408), 0.003–0.756 (Mean: 0.3805), 0.526–1.564 (Mean: 1.029), 0.07–0. 242 (Mean: 0.176), 0.002–0.02 (Mean: 0.006), 0–0.15 (Mean: 0.009), 0.001–0.001 (Mean: 0.001), 0.003–0.061 (Mean: 0.016) μg g−1 respectively. In a study in Pantai Lido, west coast of Peninsular Malaysia, mean concentrations of Cu, Cd, Fe, Ni, Pb and Zn in the shell samples of Perna viridis were 8.41, 6.67, 48.3, 40.4, 59.4, and 5.96 μg g−1 respectively [27]. Ravera et al also determined the heavy metal levels in the shell samples of Uniopictorium mancus from shallow Bay located in Ranco, Italy. They reported that the mean values Al, Cu, Zn, Fe and Mn were found to be (80.86 ± 100.48), (3.53 ± 3.29), (24.00 ± 14.63), (211.20 ± 273.71) and (461.52 ± 252.67) μg g−1 respectively [28]. In a study in Tersakan River, south-west Turkey, mean concentration of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the shell samples of Unio sp. ranged from 0.382 ± 0.06, 1.155 ± 0.08, 7.403 ± 0.54, 15.902 ± 1.24, 671.182 ± 55.05, 268.291 ± 18.24, 20.821 ± 1.77, 4.157 ± 0.21 and 8.475 ± 2.48 μg g−1 respectively [29]. Statistical analysis of Mann-Whitney U test showed that Shell samples of Trachycardium lacunosum in polluted area contained significantly higher concentrations (P < 0.05) of all measured metals (Al, Zn, Fe, Mn, Ni, Co, Cr and Cu) compared with unpolluted area (Table 4). The comparison between metal concentrations in the polluted and unpolluted areas are shown in Fig. 3.
Fig. 3

Comparison of heavy metal concentration levels in the shell samples at polluted and unpolluted area

Beside sediment that may be good indicators of long and medium term of metal loads, bivalve shell is also an indicator of metal contamination since it is sessile and sedentary and reflects the metal level of the special region [30]. In the marine environments, metals discharged from sewage or industrial effluents may be quickly transported from water column to the sediment [31]. The accessibility of various metals in sediments provides a chance for marine organisms to biomagnify these metal and later remobilized them via the food chain. The metal concentrations in the shell samples of Trachycardium lacunosum in polluted area were higher than those of the samples taken from the unpolluted area. This indicated that the polluted area had higher pollution and bioaccessibilities of heavy metals. These results are in accordance with the fact that there are different anthropogenic activities, such as petrochemical plants and harbor activities in the Nayband Bay. Use of bivalve shells for metal contamination monitoring in the aquatic environments has various advantages over that of soft tissues. The shells are simple to keep and handle and become clear to be sensitive to environmental metals over the long period. As shells growth occurs incrementally they can provide an indication over a distinct time period, unlike the soft tissues which are good accumulator of various metals and integrate the chemical pollution indication over the living of the marine organisms [32].

The findings of this study showed that Trachycardium lacunosum is a good biological indicator for all examined metals except V in the Persian Gulf coastal areas due to its capability in bioaccumulating of metals from the sediment. In a study, Palpandi and Kesavan measured the levels of metals in sediment, shell and soft tissues of mangrove gastropod Nerita Crepidularia. They have reported that the order of metal accumulation in shell and soft tissues of Nerita Crepidularia was Fe > Al > Mg > Mn > Cd > Cu > Cr > Zn > Ni > Pb. They concluded that the higher levels of metals could be due to the heavy inflow of freshwater, which brought lot of effluents from municipal drainage and irrigation channels [20]. In another study it has been reported that between measured metals, Zn had the highest concentration level in the shell samples of Perna viridis and Modiolus metcalfei in Vellar Estuary, South East shoreline of India [33]. In another study in the Egyptian Red Sea shoreline, significant spatial differences in the metal concentration levels in Tridacna maxima were observed. The concentrations of most investigated metals in the Tridacna maxima shells and sediments were higher in the anthropogenic areas compare with unpolluted areas [34].

Identification of metal interrelationships

The Spearman’s rho correlation coefficients were calculated to assess the association of metals in the sediment (Table 6) and shell samples (Table 7) in polluted and unpolluted areas.
Table 6

The Spearman’s rho correlations between metal concentrations in the sediments in polluted and unpolluted areas

  

Al

Co

Cr

Cu

Fe

Mn

Ni

V

Zn

Unpolluted area

Al

1.000

–0.306

0.505b

–0.069

0.947a

0.928a

0.632a

0.558b

0.813a

Co

 

1.000

0.015

0.358

–0.196

–0.163

–0.230

–0.269

–0.338

Cr

  

1.000

–0.293

0.549b

0.505b

0.309

0.255

0.486b

Cu

   

1.000

0.009

0.038

–0.323

–0.011

–0.124

Fe

    

1.000

0.989a

0.513b

0.474b

0.710a

Mn

     

1.000

0.486b

0.444b

0.654a

Ni

      

1.000

0.221

0.616a

V

       

1.000

0.432

Zn

        

1.000

polluted area

Al

1.000

–0.328

0.867a

0.173

0.886a

0.689a

0.757a

0.722a

0.728a

Co

 

1.000

–0.246

–0.232

–0.343

0.018

–0.238

–0.256

–0.304

Cr

  

1.000

–0.154

0.735a

0.632a

0.585a

0.656a

0.594a

Cu

   

1.000

0.141

0.203

0.143

–0.105

–0.081

Fe

    

1.000

0.767a

0.759a

0.740a

0.765a

Mn

     

1.000

0.411

0.477a

0.606a

Ni

      

1.000

0.510b

0.517b

V

       

1.000

0.751a

Zn

        

1.000

aCorrelation is significant at the 0.01 level

bCorrelation is significant at the 0.05 level

Table 7

The Spearman’s rho correlations between metal concentrations in the shells in polluted and unpolluted areas

  

Al

Co

Cr

Cu

Fe

Mn

Ni

Zn

Unpolluted area

Al

1.000

–0.042

.

–0.092

–0.130

–0.187

0.515

0.371

Co

 

1.000

.

–0.142

–0.604b

–0.376

–0.034

0.578b

Cr

  

.

.

.

.

.

.

Cu

   

1.000

0.098

–0.313

0.312

0.352

Fe

    

1.000

0.420

0.232

–0.301

Mn

     

1.000

–0.092

–0.534b

Ni

      

1.000

0.268

Zn

       

1.000

polluted area

Al

1.000

0.158

–0.224

–0.352

0.282

0.083

0.016

0.779a

Co

 

1.000

0.304

0.276

0.551b

0.191

–0.062

0.129

Cr

  

1.000

0.809a

–0.184

–0.602b

0.161

0.012

Cu

   

1.000

–0.170

–0.567b

0.230

0.006

Fe

    

1.000

0.400

0.021

0.017

Mn

     

1.000

–0.248

–0 .150

Ni

      

1.000

0.101

Zn

       

1.000

aCorrelation is significant at the 0.01 level

bCorrelation is significant at the 0.05 level

As shown in Table 4, most metals in the sediment samples in the polluted area are well correlated. Fe had remarkable positive correlations (P < 0.01) with Mn (r = 0.767), Ni (r = 0.759), V (r = 0.740), and Zn (r = 0.765). Cr had also noticeable correlations (P < 0.01) with Fe (r = 0.735), Mn (r = 0.632), Ni (r = 0.585), V (r = 0.656), and Zn (r = 0.594). In the case of Mn remarkable positive correlations (P < 0.01) were observed vs V and Zn. The significant correlation between Al and other metals (except Cu, Co) in both polluted and unpolluted areas confirms that these metals are associated with alumina silicate minerals. Similar significant positive correlations between metals in the sediment samples have been reported in different areas [25, 35]. As seen in Table 4, in the shell samples of Tracycardium lacunosum in the polluted area there are correlations for Al vs Zn (r = 0.779), Cr vs Cu (r = 0.809) and in the cases of Co vs Fe (r = 0.557), Cr vs Mn (r = – 0.602), and Fe vs Mn (r = – 0.567). The correlations were significant at the level of 0.05 in the polluted area. The significant correlations found between heavy metals could be due to several reasons such as differences in the biological half-life and biochemical behaviors of metals found in the sediments and shells [3638].

Conclusion

In this work, the levels of metals including Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu were determined in the sediment and shell samples of the bivalve Tracycardium lacunosum from two areas (polluted and unpolluted) of Asaluyeh Bay, northern part of the Persian Gulf. This study was the first effort to consider shell of Tracycardium lacunosum as a bioandicator for monitoring of heavy metals. Results of this study indicated that all measured metals including Al, Zn, Fe, Mn, Ni, V, Co, Cr and Cu were significantly higher in the sediment samples of polluted area compared with unpolluted area. In the case of shell samples of Trachycardium lacunosum, polluted area contained significantly higher concentrations of Al, Zn, Fe, Mn, Ni, Co, Cr and Cu compared to unpolluted area. It was concluded that shells of the Trachycardium lacunosum can be applied as a suitable bioandicator for heavy metals in the marine environment. Results confirmed that due to the possible pollution by oil and gas activities near the polluted area continuing and permanent evaluating as well as mitigation measures in this area is highly necessary.

Abbreviation

ICP-OES: 

Inductively Coupled Plasma-Optical Emission Spectrometry.

Declarations

Acknowledgements

The authors are grateful to the Bushehr University of Medical Sciences for their financial support and the laboratory staff of the Environmental Health Engineering Department for their cooperation. This project was partly supported by Iran National Science Foundation (Research Chair Award No. 95/INSF/44913).

Funding

This study was performed as a master thesis in Environmental Health Engineering founded by Bushehr University of Medical Science

Availability of data and materials

Additional data from the study are available by request to the corresponding author by email.

Authors’ contributions

VNK was the main investigator, collected the data, and wrote the first draft of the manuscript. SD was the supervisor of study in all steps, edited and polished the final version of manuscript. IN has guided and collected the samples. AO performed the statistical analysis. AV, MN, MR and SN were advisors of the study. MK and RM conducted the experiments. All authors read and approved the final version of manuscript.

Competing interests

The authors declare that they have no competing interests.

Consent for publication

Not applicable.

Ethics Approval and Consent to Participate

Not applicable.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Department of Environmental Health Engineering, Faculty of Health, Bushehr University of Medical Sciences
(2)
The Persian Gulf Marine Biotechnology Research Center, The Persian Gulf Biomedical Sciences Research Institute, Bushehr University of Medical Sciences
(3)
Systems Environmental Health, Oil, Gas and Energy Research Center, The Persian Gulf Biomedical Sciences Research Institute, Bushehr University of Medical Sciences
(4)
The Persian Gulf Tropical Medicine Research Center, The Persian Gulf Biomedical Sciences Research Institute, Bushehr University of Medical Sciences
(5)
The Persian Gulf Studies and Researches Center Marine Biotechnology Department, Persian Gulf University
(6)
School of Public Health, Tehran University of Medical Sciences
(7)
Ecology Department, Iranian Shrimp Research Institute

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Copyright

© The Author(s). 2016

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