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Comparative study of heavy metal (Cd, Fe, Mn, and Ni) concentrations in soft tissue of gastropod Thais mutabilis and sediments from intertidal zone of Bandar Abbas.

Introduction

Metals transport to aquatic environment from natural sources such as volcanic emissions, forest fires, and anthropogenic sources such as urban, industrial & agriculture wastes, fossil fuels, garbage & solids wastes dump and etc [14,18].

Metal pollution can affect sediments and organisms and have a risk to human health [19,10]. To determine the amount of metals in aquatic environments can be analyzed water, sediments and marine organisms. Biomonitoring can provide useful information to determine the metals pollution in aquatic ecosystem [32,19,34,10].

The use of soft tissue of marine snails is not a new suggestion since numerous studies have already been reported [27,13,16,12,18,10]. There are, however, several factors (age, size, sex, sexual state and physiological functions) that affect metal accumulation in the soft tissue of molluscs. From these factors body size play a major rule for accumulation of metals in soft tissue [7,11,8,13,31,12,10].

Chan [11] suggested that levels of metals accumulated in some marine organisms may be more than its value in background which demonstrate the potential of species as bioindicators of metal pollution [19]. Moreover, studying the relationships between the concentrations of pollutants in the sediments and organism can be a valuable tool to assess the contamination levels [10].

Muricids occur in all warm waters, especially within the tropics and prey upon invertebrates, including other molluscs such as barnacles and bivalves [6]. Thais mutabilis (Link, 1807) is one of the caenogastropod muricids and lives on muddy littoral rocks (FAO web site).

Previous studies, however, have shown that the Persian Gulf receives contaminant metals by various industrial outputs (including: thermal power plant and oil refinery in Bandar Abbas [22,25].

The aims of this study were: (a) to determine the levels of metals in soft tissue of gastropod Thais mutabilis and sediments from intertidal zone of Bandar Abbas; (b) to assess the existence of length dependent differences in metal contents of the Thais mutabilis; and (c) to study if the species of Gastropod analyzed could be acceptable biomonitors of metal pollution in the Persian Gulf and other similar systems.

Materials and Methods

2.1 Study area:

The Persian Gulf is large basin with an average depth of 35-40 m, a total area of around 240,000 km2. The northern part of Persian Gulf, Due to the low depth, restricted rotation; high salinity and temperature are much more affected by pollutants [28,1,22,4]. Three stations were selected for the sampling from the tidal shores of Bandar Abbas (NE Persian Gulf) during low tides in January 2011 (Fig. 1). Sampling location position was detected using GPS (Table 1).

[FIGURE 1 OMITTED]

2.2 Thais mutabilis Sampling and Analysis:

Nine subsamples of a marine snail, Thais mutabilis Link, 1807(Mollusca, Gastropoda) were collected by hand at each station. Samples were rinsed with seawater from their sampling locations and were put in acid-washed polyethylene bags and transported to the laboratory [24]. In the laboratory, samples were sized and placed in acid-washed polyethylene bags and frozen at -20[degrees]C until analysis. At a later date, the whole soft tissues were removed from their shells by using a stainless steel crusher and rinsed quickly with distilled water. All soft tissues of marine snails were dried at 105[degrees]C until constant dry weight (dw) [3]. Then 0/5 g of each dried tissues with three replicates were digested in concentrated HNO3 & HCL[O.sub.4] (Merck) in the ratio of 3:1. Samples were put into a hot-block digester at 140[degrees]C for at least 1.5 h [3]. The digested samples were filtrated by using filter paper (Whatman No. 42) and diluted with double deionized water appropriately in the range of standards which were prepared from stock standard solution of the metals (Merck). After dilution, the metals contents of tissues, Cd, Fe, Mn and Ni were analyzed by using flame atomic absorption spectrometer (Varian, model AA-220) and metals concentration in soft tissues were presented as microgram metal/gram dry weight.

2.3 Sediments Sampling and Analysis:

At each station, three subsamples of sediment were taken (top 10 cm), put in acid-washed polyethylene bags, and homogenized. In the laboratory, sediment samples were dried at 105[degrees]C until constant dry weight [2]. The dried sediment samples were sieved through a 0/5 mm aperture stainless steel sieve and were shaken vigorously to produce homogeneity. For the analyses of total Cd, Fe, Mn and Ni concentrations in the sediment samples 0/5 g of each dried sediment samples with three replicates were digested in concentrated HNO3 & HCL[O.sub.4] (Merck) in the ratio of 3:1.Samples were put into a hot-block digester at 140[degrees]C for at least 1.5 h [2]. The digested samples were filtrated by using filter paper (Whatman No. 42) and diluted with double deionized water appropriately in the range of standards which were prepared from stock standard solution of the metals (Merck). Metals were measured in the same equipment as in the case of the molluscs.

2.4 Statistical Analysis:

Statistical analysis was performed with SPSS 18.0 software. One-way ANOVA of variance with the 95% confidence interval followed by a Tukey HSD test was accepted to check the differences between concentrations of metals in the T. mutabilis and sediment samples in different stations.

Pearson correlation & Regression analysis was used, to test the relationships among the characteristics of the sediments and metal concentrations in the T. mutabilis, although to test the relationships between body size and metal concentrations in T. mutabilis.

3. Results:

3.1 Sediments:

Concentrations of metals in sediment samples indices are in Fig. 2 and Table 3. The highest concentrations in sediments for all metals (Cd: 1/8433 [+ or -] 0/06351, Fe: 10717/1767 [+ or -] 1052/99211, Mn: 417/3067 [+ or -] 33/16178 & Ni: 53/7300 [+ or -] 10/89053) were recorded at station 2.

The one way analysis of variance (ANOVA) performed; no significant differences (P > 0.05) were recorded between the concentrations of Fe, Mn, and Ni in the sediment samples from the three stations. Significant differences (P > 0.05) were recorded between the concentrations of Cd in the sediment samples from the station 1 & 2 with 3.

The pattern of the metal occurrence in the sediments of all the stations could be arranged in the following sequence:

Fe > Mn > Ni > Cd (Fig. 2).

3.2 Thais mutabilis:

Specimens of T. mutabilis could be collected at all the sampling sites. Total length (size range) of T. mutabilis at three stations are given in Table 2. T. mutabilis specimens that collected from station 1 was significantly smaller than those collected from the other stations (p < 0.05).

Concentrations of metals in soft tissues of T. mutabilis varied as follows ([micro]g[g.sup.-1] d.w.): Cd between 12/9822 [+ or -] 10/64148 (station 1) and 4/4178 [+ or -] 3/43636 (station 2); Fe between 403/6433 [+ or -] 116/80310 (station 3) and 252/2744 [+ or -] 104/21001 (station 2); Mn between 17/9578 [+ or -] 8/41192 (station 1) and 15/9644 [+ or -] 5/43223 (station 3); Ni between 3/8778 [+ or -] 2/90094 (station 2) and 2/6567 [+ or -] 1/35648 (station 1)(Fig. 3).

The one way analysis of variance (ANOVA) performed; no significant differences (P > 0.05) were recorded between the concentrations of Fe, Mn, and Ni in the T. mutabilis samples from the three stations. Significant differences (P < 0.05) were recorded between the concentrations of Cd in the T. mutabilis samples from the station 2 with 1.

The pattern of the metal occurrence in the soft tissues of T. mutabilis of all the stations could be arranged in the following sequence:

Fe > Mn > Cd > Ni (Fig. 3).

Size dependent relationship with the metal content measured in T. mutabilis is shown in Fig. 4. These figures shows that for Cd, content increases with the decrease of length, as expressed by the strong negative relationships between metal content and total length (p < 0.0001, r = - 0.640).

Relationships among the metal concentrations in the sediments and in T. mutabilis are shown in Fig. 5. Only the significant positive correlation was found between Ni Concentration in T. mutabilis and in the sediments (p < 0.0001, r = 0.941).

Discussion:

The results of the present study show that the highest concentrations in sediments for all metals that were recorded at station 2.This founding may be attributed to one or more of the following reasons:

(a) The motor-boats traffic in the Posht-e-shahr waterfront entering the engine oil and the entry of oil pollution.

(b) Discharge of untreated municipal sewage [18] from the city of Bandar Abbas.

(c) A large amount of waste had been accumulated in this station that, leaching of metals from solids wastes dump [18].

The one way analysis of variance (ANOVA) performed, significant differences (P > 0.05) were recorded between the concentrations of Cd in the sediment samples from the station 1 & 2 with 3 .This finding can, at the first station for urban waste water effluent and in the second station due to factors listed above (a, b and c). So, Cadmium contamination in the first and second station is more than the station 3, the sewage effluent that is no more.

[FIGURE 2 OMITTED]

Maximum and minimum value of Fe (10717/1767 [+ or -] 1052/99211 - 9420/0800 [+ or -] 340/08055) & Mn (417/3067 [+ or -] 33/16178 - 368/4467 [+ or -] 9/47498) in sediments was recorded at same station, 2 and 1 respectively. This is in confirmation with the findings of Hamed and Emara [19], this can be described by the reality that their hydroxides are impulsive together in the bottom [26], and the chemical science [5].

Results in Table 3 showed that Fe levels in sediments from all stations were within the recommended values (41000.00 [micro]g[g.sup.-1)] of unpolluted marine sediments [17,29]. Mn levels in sediments from all stations were within the recommended values (770.00 [micro]g[g.sup.-1]) of unpolluted marine sediments [29]. Cd levels in sediments from all stations were higher than the recommended values (0.11 [micro]g[g.sup.-1)] of unpolluted marine sediments [17,29,20], may be due to discharges of untreated municipal sewage [21], from the city of Bandar Abbas. Ni levels in sediments at stations 1 & 3 were high, but at station 3 exceeded than the high alert levels (HAL: 50 [micro]g[g.sup.-1)] [33], this may be due to oil pollution [25,19].

[FIGURE 3 OMITTED]

Margalef [23] indicated that biological communities existing in polluted sites had an upper growth rate because the low number of species accomplished of tolerating the most stressful conditions reduces competition and facilitates admission to the resources by the adapted organisms. The larger size of T. mutabilis specimens collected in the station 2; seem to be in agreement with this finding.

The highest concentrations belonging to iron and manganese in the soft tissues of T. mutabilis was generally seen in marine gastropods, because these are essential elements incorporated in proteins, respiratory proteins and enzymes [19,12,9,30].

The highest concentration of Cd in soft tissues of T. mutabilis specimens was observed at station 1 and the lowest at station 2. This can be explained by size of samples, because concentration of Cd in soft tissues of T. mutabilis specimens was showed strong negative relationships with total length (p < 0.0001, r = - 0.640).

T. mutabilis specimens at station 1 had lowest size and at station 2 had upper. According to studies on aquatic animals, concentration of cadmium decreases with increasing size, because the concentration of metals in the younger animals, that have smaller size, is higher due to higher metabolic activity [8,9].

Cervantes et al. [10] indicated that Hexaplex trunculus belongs to the family of Muricidae satisfies all the requirements to be a biomonitor of metal contamination as they are abundant, sedentary, easy to identify, and tolerate high concentrations of metals. T. mutabilis too belongs to the same family and has similar features of the intertidal zone also (1) provide sufficient tissue for analysis, (2) the main positive correlation was found between concentration of Ni in T. mutabilis and sediments (p < 0.0001, r = 0 .941), and (3) the concentration of Cd in soft tissues of T. mutabilis was more than its value in sediments, so it could be used as bioindicator for heavy metals Cd and Ni.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Acknowledgment

M. Astani would like to thank Dr. Musazadeh, Eng. Moassesi and Eng. Farzin from environmental Laboratory of the Atomic Energy Organization of Iran, also all the members of the Persian Gulf and Oman Sea Ecological Research Institute. Special thanks to Eng. M.E. Noorian, Eng. Mariam Astani & E. Roozbahan.

References

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(1) M. Astani, (1) A.R. Vosoughi, (1) L. Salimi, (2) M. Ebrahimi

(1) Islamic Azad University, North-Tehran branch, Iran.

(2) Persian Gulf and Oman Sea Ecological Research Institute, Bandar Abbas, Iran.

Corresponding Author

M. Astani, Islamic Azad University, North-Tehran branch, Iran.

Ph: +989122061138 E-mail: mahsaastani@yahoo.com
Table 1: Geographical information of sampling area in Bandar Abbas
coast, winter 2011.

Name of area Station X

South Golshahr 1 E 56[degrees]19.294
Posht-e-shahr waterfront 2 E 56[degrees]15.647
Soro 3 E 56[degrees]14.850

Name of area Y

South Golshahr N 27[degrees]10769
Posht-e-shahr waterfront N 27[degrees]10163
Soro N 27[degrees]09.391

Table 2: Total length of T. mutabilis at three stations in the Bandar
Abbas coast, winter 2011 (mm).

 n Min Max Mean [+ or -] 1 SD

Station 1 9 37/51 46/30 41/05 [+ or -] 3/35
Station 2 9 44/19 52/38 48/01 [+ or -] 2/56
Station 3 9 44/30 50/33 47/47 [+ or -] 2/15

Table 3: Comparison of detected values (mean [+ or -] SD) of metals
with recommended values of unpolluted sediments ([micro]gg-1).

Metal Station 1 Station 2

Fe 9420/08 [+ or -] 340/08 10717/17 [+ or -] 1052/99
Cd 1/77 [+ or -] 0/07 1/84 [+ or -] 0/06
Mn 368/44 [+ or -] 9/47 417/30 [+ or -] 33/16
Ni 44/56 [+ or -] 2/30 53/73 [+ or -] 10/89

Metal Station 3 Recommended value

Fe 10493/51 [+ or -] 294/37 41000.00 *
Cd 1/57 [+ or -] 0/06 0.11 **
Mn 400/02 [+ or -] 13/75 770.00 ***
Ni 42/9767 [+ or -] 1/37493 50 ****

* (GESAMP, 1982; Salomons and Froster, 1984).

** (GESAMP, 1982; Salomons and Froster, 1984; IAEA, 1989).

*** (Salomons and Froster, 1984).

**** (USEPA, 1996).
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Title Annotation:Original Article
Author:Astani, M.; Vosoughi, A.R.; Salimi, L.; Ebrahimi, M.
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:7IRAN
Date:Jan 1, 2012
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