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Original ArticleAssessment of Trace Metals in Surface Water and Sediment

Collected from Polluted Coastal Areas of BangladeshMohammad Raknuzzamana,b, Md Kawser Ahmedc, Md Saiful Islamd, Md Habibullah-Al-Mamuna,b,

Masahiro Tokumuraa, Makoto Sekinea, Shigeki Masunagaa

a Graduate School and Faculty of Environment and Information Sciences, Yokohama National University, Yokohama, Japan

b Department of Fisheries, University of Dhaka, Dhaka, Bangladeshc Department of Oceanography, University of Dhaka, Dhaka, Bangladesh

d Department of Soil Science, Patuakhali Science and Technology University, Dumki, Patuakhali, Bangladesh

ABSTRACTAccumulation of trace metals in coastal ecosystem has become a prodigious problem in Bangladesh. This study was conducted to determine seven trace metals concentration (Cr, Ni, Cu, Zn, As, Cd and Pb) in water and sediment samples collected from coastal sites of Bangladesh. Water of Cox’s Bazar hatchery site showed the highest levels of Zn (1,390 µg/L), Cu (510 µg/L) and Pb (109 µg/L), which attributed to huge discharge of different chemical compounds from the hatcheries and fish processing industries. Trace metals in water samples were in the range of Cr (2.6 − 15.3 µg/L), Ni (5.1 − 77.5 µg/L), Cu (10.2 − 510 µg/L), Zn (5.0 − 1,390 µg/L), As (2.1 − 13.3 µg/L), Cd (0.006 − 0.09 µg/L), Pb (0.4 − 109 µg/L), respectively. The elevated concentration of As (13.3 µg/L) was observed in water sample of Chittagong ship breaking area. Some metals (Zn, Cu, Pb and As) in water exceeded the international quality guidelines. Sediment samples of Chittagong ship breaking area showed the highest level of Cr (56 mg/kg dw), Ni (37 mg/kg dw), Cu (28 mg/kg dw) and Pb (41 mg/kg dw) which exceeded the Canadian Sediment Quality Guidelines. The elevated level of trace metals in this Bangladeshi coastal ecosystem should not be ignored and immediate control measure is recommended.

Keywords: Trace metals, coastal pollution, sediment, Bangladesh

INTRODUCTION

In recent years, the accumulation of trace metals in aquatic ecosystems has become a problem of great concern throughout the world [1,2]. The concern is growing more and more serious globally especially in developing countries like Bangladesh [3,4]. Sediments are ecologically important serving as a reservoir of contaminants due to remobilization, desorption, degradation and redox reactions, which playing a significant role in maintaining the trophic status of water body [5]. It is an appropriate matrix to monitor the contami-nation of trace metals in the aquatic environment [6]. It acts as adsorptive sink for metals since they can scavenge some elements, thus, naturally higher metal concentration is found in sediment than in water column. Trace metals contamina-

tion in sediment has been regarded as a critical problem of coastal ecosystem due to their toxicity and bioaccumulation [7]. Trace metal residues in contaminated habitats may ac-cumulate in microorganisms, fishes, crustaceans and other aquatic animals which may enter into the human food chain and result in health problems [1,8].

Bangladesh is a riverine country with a large marshy jungle coastline of 580 km in the Bay of Bengal. The river Ganges and Yamuna have been one of the major recipients of industrial effluents from India entering in to Bangladesh as Padma and Jamuna. The river Padma and the river Ja-muna are joined together in Chadpur forming the Meghna river which dumping up the waste materials through Bhola estuary to the Bay of Bengal. Besides, the rapid inadvertent industrialization, urban expansion, enormous population

Corresponding author: Mohammad Raknuzzaman, E-mail: mohammad-raknuzzaman-jc@ynu.jpReceived: June 23, 2015, Accepted: January 25, 2016, Published online: August 10, 2016Copyright © 2016 Japan Society on Water Environment

Journal of Water and Environment Technology, Vol.14, No.4: 247–259, 2016doi: 10.2965/jwet.15-038

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growth and overall trans-boundary water issue contribute massive amounts of domestic wastewater and untreated industrial effluents into the sea through rivers. The waste materials coming through these rivers are also accelerating the pollution of coastal water and sediment that might con-taminate the fish, crustaceans and others aquatic biota which may become a public health concern in future.

But, in the Bangladesh context, the concerned authorities and general people have not been aware and no complete study carried out so far regarding this issue. Thus, the aim of the study is to determine the concentrations of certain trace metals (Cr, Ni, Cu, Zn, As, Cd and Pb) and their spatial and temporal distribution in surface water and sediment which were collected from the coastal areas of Bangladesh.

MATERIALS AND METHODS

Study area and sampling locationFour sampling sites (Cox’s Bazar, Chittagong, Meghna Es-

tuary and Sunderbans) with three different locations of each were investigated in the southeast and southwest coastal area of Bangladesh (Fig. 1). The first site (St. 1) was located at the southeast coastal area in Cox’s Bazaar which lies be-tween latitudes 21°27′02″N to 21°26′33″N and longitudes 91°58′16″E to 91°57′01″E. Cox’s Bazar was a seaside tourist town with an unbroken 125 km world’s longest natural sandy sea beach. Considering two diverse ecological aspects, it was

divided into two sub sites (Bakkhali estuary and hatchery site). The Bakkhali estuary was regarded as an important economic part within the Coax’s Bazar district with a harbor and imperative local fishery presenting a variety of coastal ecosystem types. The ehstuary was about 0.5 km wide and > 10 m deep at its mid-point and directly influenced by semi-diurnal tides. This estuarine zone was characterized by the long intertidal mudflat which was linked to the Bay of Bengal in the Indian Ocean, with the spring tide amplitude of 3 m. Moreover, Moheshkhali Island is one of the important tourist attracting economic zone incorporating to Bakkhali estuary through 9 to 11 kilometer long Maheshkhali chan-nel to Cox’s Bazaar Central Island. Likewise, hatchery site was very close (200 − 300 m) to the sea beach along with sampling sites where more than 53 shrimp hatcheries and aquafarms, big fish landing centers, huge hotels for amuse-ment of tourists and some industries were located. Coastal shrimp culture has been widely practiced in this coast since a couple of decades. So, these sampling areas were mostly in-fluenced by the chemicals and wastage from these unplanned industries, hatcheries and aquaculture farms.

The second site (St. 2) was located near the Chittagong port and ship breaking area which lies between latitudes 22°13′27″N to 22°38′22″N and longitudes 91°48′14″E to 91°32′45″E. This is the southeastern principal seaport region of the country, straddling the hills at the estuary of the Kar-naphuli River which regarded as industrial and commercial

Fig. 1 Map showing sampling sites in the coastal area of Bangladesh.Source- http://bluegoldbd.org/more-information/maps/

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hubs. There are more than 8,542 industrials establishments dealing with cement clinker, fertilizers, steal rerolling, paper and pulp, rubber and plastic, oil refinery, beverages, sugar, pharmaceuticals, tobacco, jute, textiles, fish processing, tannery, paint, rechargeable batteries, jewelry, plating, auto-mobile engine, electronics industries in the coastal area [9] which are adjacent to the sampling sites. Besides, Chittagong ship breaking yard is world’s second largest ship breaking area confined to 18 km2 area along the coast of Sitakund Upazilla specially Bhatiary to Kumira in Chittagong divi-sion in Bangladesh. Ship breaking is a type of ship disposal involving the breaking up of ships for scrap recycling, with the hulls being discarded in ship graveyards. Various reuse and disposable materials were discharged and spilled from scrapped ships, and these often get mixed with the beach sediment and seawater. While dismantling the ships, the in-dustry generated all kinds of miscible and immiscible wastes in the form of solids, liquids and gases which accumulated over the soil first and then migrated incrementally to the tidal zone, sub-tidal zone, and subsequently to the deep seawater and into the respective sediments.

The third site (St. 3) was located near the Meghna Estu-ary in Bhola which lies between latitudes 22°28′07″N to 22°20′39″N and longitudes 90°49′41″E to 90°50′31″E. This is an estuarine area where the main rivers mix together to the Bay of Bengal containing the industrial effluents through inland rivers from country and trans-boundary countries.

The last site (St. 4) was located near the southwest part of coastal area of Sundarbans that is regarded as a large man-grove ecosystem in Bangladesh which lies between latitudes 22°34′43″N to 22°18′02″N and longitudes 89°32′48″E to 89°36′26″E.This sampling area was also mostly influenced by different anthropogenic and industrial activities like cement factories, export processing zone, sea port, paper industries, oil refinery industries, steal rerolling, fertilizer industry, hatcheries and aquafarms, fish processing indus-tries, leather industries, dyeing industries, paint industries etc. in Khulna and Mongla area. However, in Bangladesh context, no reliable data regarding how much the industries contribute pollution in the coastal area.

Sample collection and preparationThe sampling was conducted during the transition of sum-

mer and rainy season starting from early August to early September in 2013. The reasonable and adequate ground for the selection of seasons were to estimate the fluctuation of trace metals concentration in both water and sediment in relation to the variation of the physico-chemical properties,

as the industrial and agricultural activities like fish process-ing, aquafarm operation, hatcheries, crop cultivation and ship dismantling activities are vigorously increased in the sampling sites during this particular period. The tide in the coastal and estuarine area were semi-diurnal (two nearly equal high and low tides each day) and the samples were col-lected during the period of low tide. Unfiltered surface water samples were collected from four coastal sampling sites with three different stations of each. Immediately after collection, the samples were transferred into 100 mL polypropylene bottles which were previously washed with dilute nitric acid and deionized water. Then the samples were stored in refrig-erator in the Department of Fisheries, University of Dhaka, Bangladesh. The coastal surface sediment samples were taken at a depth of 0 to 5 cm using a portable Ekman grab sampler. Three composite samples of mass approximately 200 g were collected at each station. Composite sediment samples were collected into polyethylene air tight bags in the field and transported to the laboratory for pre-treatment. The samples were dried in oven at 105°C for 24 h to gain constant weight. The dried samples were then ground us-ing mortar and pestle and sieved through 106 µm aperture and stored in labeled high density polyethylene (HDPE) bottles until chemical analyses. The all processed samples were brought to Yokohama National University, Japan for chemical analysis under the permission of Yokohama Plant Protection Station.

Analytical methods for physicochemical parametersThe physicochemical parameters such as pH, salinity, sus-

pended solids (SS) and temperature (Temp.) of water were measured immediately after sample collection by multi water quality checker (U-50, Horiba, Ltd., Kyoto, Japan). For the analysis of percent carbon (%C) and percent nitrogen (%N) in sediment samples, about 1.33 g of dried sediment samples of each was analyzed by using an organic elemental analyzer (Macro Coder JM1000CN, J-Science Lab Co., Ltd., Kyoto, Japan). Different concentrations (20, 35, 50, 70 and 85 mg) of hippuric acid (standard) were used to prepare the calibration curves of carbon (C) and nitrogen (N). The percentage of C and N in sediment samples were determined by external calibration method.

Sample digestion and metal extractionA microwave digestion was used to digest the samples for

analysis. All chemicals were analytical grade reagents and Milli-Q (Elix UV5 and Milli-Q Adv.A10, Millipore, USA) water was used for each solution preparation. The PTFE

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(polytetrafluoroethylene) digestion vessels and polypropyl-ene containers were cleaned, soaked in 5% HNO3for more than 24 h, then rinsed with Milli-Q water and dried. For metal analysis, 20 mL water sample, 0.2 g of sediment sam-ples of each were treated with 5 mL 69% HNO3 acid (Kanto Chemical Co, Tokyo, Japan) and 2 mL 30% H2O2 (Wako Pure Chemical Industries, Tokyo, Japan) in the digestion vessels. By stirring carefully with a Teflon bar, the vessels containing mixtures were kept undisturbed for 20 minutes in the draft chamber (Fumehood, CBZ-Vc18-H1, Shimadzu, Kyoto, Japan). Then the vessels were placed in a microwave digestion system (Berghof-MWS2, Berghof speedwave®, Eningen, Germany). The following microwave program was applied: 10 min at 180°C with 800 W, 10 min at 190°C with 900 W, and as a last step 10 min at 100°C with 400 W. After digestion, acid solutions with samples were transferred into a Teflon graduated cylinder and total volume was made up to 50 mL with Milli-Q water. The digested acid solutions were then filtered by using syringe filter (DISMIC®- 25HP PTFE, pore size = 0.45 µm; Toyo Roshi Kaisha, Ltd., Tokyo, Japan) and stored in 50 mL polypropylene tubes (Nalgene, NY, USA).

Instrumental analysisFor trace metals, samples were analyzed using inductively

coupled plasma mass spectrometer (ICP-MS, Agilent 7700 series, USA) (Table 1). Multi-element Standard XSTC-13

(SPEX CertiPrep®, USA) solutions was used to prepare calibration curve. The calibration curves with R2 > 0.999 were accepted for concentration calculation. Before starting the sequence, relative standard deviation (RSD < 5%) was checked by using tuning solution (1 µg/L each of Li, Y, Ce, Tl, Mg and Co in 2 wt% HNO3) purchased from Agilent Technologies. Internal calibration standard solution contain-ing 1.0 mg/L each of Beryllium (Be) and Tellurium (Te), and 0.5 mg/L each of Indium (In), Yttrium (Y), Cobalt (Co) and Thallium (TI) was purchased from SPEX CertiPrep®, USA and it was added into each sample. Working standards (0, 10, 20, 50 and 100 µg/L) were prepared by dilution of a multi-element stock solution (Custom Assurance Standard, SPEX CertiPrep®, USA), then the concentrations of trace metals were determined by an internal standard method.

All test batches were evaluated using an internal quality approach and validated if they satisfied the defined Internal Quality Controls (IQCs). For each batch experiment, one blank, one certified reference material (CRM) and several samples were analyzed in duplicate to eliminate any batch-specific error. Finally, the concentration of trace metals were quantified by calibration based on internal standards.

Quality control and quality assuranceThe quality of total acid digestion of the sediment was

checked by using a certified reference material (NMIJ CRM 7303-a, Lake sediment) purchased from the National Insti-

Table 1 Operating conditions for ICP-MS and parameters for metal analysis.Operating conditionsNebulizer pump (rps) 0.1RF power (W) 1,550Rf frequency 27.12 MHZ

Sample depth (mm) 9 mm from load coilPlasma gas flow rate (L/min) 15Make up gas flow rate Ar 0 L/minCarrier gas (Ar) flow rate (L/min) 1.0 (optimized daily)Collision gas mode He 4.0 mL/minMeasurement parametersScanning mode Peak hopResolution (amu) 0.7Readings/replicate 1No. of replicates 3Correction equations for interferences Li [6]: [6] × 1 − [7] × 0.082

In [115]: [115] × 1 − [118] × 0.014 Pb [208]: [208] × 1 + [206] × 1 + [207] × 1

Isotopes 52Cr, 60Ni, 63Cu, 65Zn, 75As, 111Cd, 208Pb

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tute of Advanced Industrial Science and Technology (AIST), and yielded good accuracy of analysis. Comparison is made with the certified values, which in both cases confirmed that the sample preparation and instrumentation conditions provided good levels of accuracy and precision (Table 2).

Statistical analysisThe data were statistically analyzed by using the statistical

package, IBM SPSS 22.0 (Armonk, NY, USA). A Pearson bivariate correlation was used to evaluate the relationship among the inter-elemental and physic-chemical parameters. Both p value < 0.05 and < 0.01 were considered for statisti-cally significant.

RESULTS AND DISCUSSION

Concentration of trace metals in waterMean values of physical-chemical parameters and metal

concentrations of different coastal water samples from Ban-gladesh are shown in Table 3 and Fig. 2 respectively. A wide range of metal concentrations were observed among the sampling sites. Factors such as salinity, SS, pH, Temp., geomorphological setup, and terrestrial runoff might have played a role in the variation of metals. Trace metals in water samples ranged over following intervals: Cr: 2.6 − 15.3; Ni: 5.1 − 77.5; Cu: 10.2 − 510; Zn: 5.0 − 1,390; As: 2.1 − 13.3; Cd: 0.006 − 0.09; Pb: 0.4 − 109 µg/L. The mean concentrations of studied metals in water followed a decreasing order of Zn

Table 2 Analysis of trace metals from certified reference materials (NMIJ CRM 7303-a; Lake sediment) by ICP-MS (Mean ± SD, mg/kg-dw).

Metal Certified value (mg/kg-dw)

Measured value (mg/kg-dw)

(n=3)

Average recovery (%)

Cr 39.1 ± 2.8 38.7± 0.21 99Ni 21.8 ± 2.5 22.3 ± 0.90 102Cu 23.1 ± 3.1 25.7 ± 0.97 111Zn 107 ± 5.0 105 ± 3.64 98As 8.6 ± 1.0 9.1 ± 0.28 106Cd 0.34 ± 0.017 0.35 ± 0.02 102Pb 31.3 ± 1.10 32.7 ± 9.35 105

Table 3 Mean (± SD) values of physical-chemical parameters and metal concentrations (µg/L) in water samples.Sampling sites pH Temp.

(°C)Salinity

(‰)SS

(mg/L)Cr

(µg/L)Ni

(µg/L)Cu

(µg/L)Zn

(µg/L)As

(µg/L)Cd

(µg/L)Pb

(µg/L)St. 1. (a) Cox’s Bazar Bakkhali estuary (n=3)

Mean SD

6.0 0.5

22.0 1.3

11.8 5.7

110 53

2.6 0.3

5.1 1.1

239 229

12.4 11.9

5.9 4.1

0.02 0.01

0.4 0.4

St. 1. (b) Cox’s Bazar Hatchery (n=3)

Mean SD

5.8 0.8

21.5 0.6

23 0.9

413 163

8.8 10.9

12.4 11.2

510 336

1390 2390

9.0 3.0

0.09 0.10

109 189

St. 2. (a) Chittagong port (n=3)

Mean SD

5.3 0.8

23.5 0.3

15.5 2.3

497 55

8.3 2.6

9.0 2.7

20.3 4.9

5.5 7.1

2.3 0.4

0.006 0.003

2.6 0.9

St. 2. (b) Chittagong ship breaking (n=3)

Mean SD

4.7 0.8

24.7 1.0

16.8 1.5

552 86

6.3 2.1

12.3 3.9

14.3 5.5

17.1 5.5

13.3 4.4

0.04 0.02

3.6 2.6

St. 3. Sunderbans (n=3)

Mean SD

6.0 0.5

22.8 0.8

5.0 2.6

1220 312

15.3 5.5

77.5 112

163 281

342 572

2.3 0.4

0.03 0.03

6.9 2.3

St. 4. Meghna estuary, Bhola (n=3)

Mean SD

7.7 1.0

22.7 0.6

4.8 2.5

673 201

11.8 1.4

10.5 1.8

10.2 13.9

5.0 8.2

2.1 0.1

0.01 0.001

5.8 1.5

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> Cu > Pb >Ni > Cr > As > Cd. Among the trace metals ana-lyzed, the highest mean concentration of Zn (1,390 µg/L), Cu (510 µg/L) and Pb (109 µg/L) was observed in water samples at Cox’s Bazar hatchery site respectively. Cox’s Bazar is a seaside tourist town with longest sandy sea beach where 53 fish hatcheries, a fish landing center, ship and boat making industries, paint industries, salt industries, fish processing zone, garment factories, unplanned urbanization, many ho-tels and huge regular tourists can be found. The high metal concentration might be attributed to discharge of different salts and chemicals from hatcheries, fish processing indus-tries and some aqua farms through their underground pipe-line outlets to the sea without treatment. In common, zinc oxide (ZnO) is broadly used in aqua farms and hatcheries for the oxygen supply to fry and fingerlings [10]. Besides, most of the domestic sewages of Cox’s Bazar city were incorporated to the Bakkhali River through different uncontrolled canals to the Sea. The biggest fishery landing center was located in this site and was discharged all poisonous effluent directly to the river without treatment. Along the banks of this River, a dock yard has been recently developed to repair fishing and trawling boats. Waste discharge and chemical spills associ-ated with boat repairing industries represent an additional source of pollutants to the water and sediments. Moreover, galvanizing steel, ship repairing, painting, textile and dye-ing, rubber industries also contribute significant amount of Zn in this area. Considering ship repairing, painting and

coating, a huge amount of commercial paints containing zinc oxide (ZnO) and zinc sulphide (ZnS) have long been used as anticorrosive coatings in different type of boats, fishing trawlers and ships in Cos’x Bazar and Chittagong coast to protect wood and steel structures under normal atmospheric conditions, as well as to underwater steel surfaces of these water vehicles. Zinc oxide is also used to retain their flex-ibility and adherence on such surfaces for many years and using component in many formulations of durables and protective paints. Besides, the rubber industry in general, and tire manufacturers in particular, are the largest users of ZnO. It is utilized to activate the organic accelerator, serves as an effective co-accelerator in the vulcanization process, and inhibits the growth of fungi, with sufficient stability, as part of the production process of latex foam rubber products.

One of the unique properties of Zinc oxide is its ability to retain over many months of shelf-storage the tack of uncured rubber compounds for adhesive tapes (http://www.numinor.com). Furthermore, zinc sulphate (ZnSO4) and zinc chloride (ZnCl2) are widely used in textile industries like dyeing, printing, sizing and weighting of fabrics [11]. Nevertheless, due to the scarcity of discharge data, the load from such in-dustrial establishments cannot be calculated exactly that of how much of these pollutants contribute metals contamina-tion in this area.

Copper in aqueous systems received attention mostly because of its toxic effects on biota. Copper has been used

Fig. 2 Box plot showing the trace metal concentrations (µg/L) in water samples (n = 18).

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as disinfectant chemical in aquatic farms and aquaculture operations. It is broadly used as an effective algaecide and in some parasites treatment. The cheapest and most commonly used form is copper sulfate, which is available either as a crystal or a powder often known as “Bluestone” or “Blue powder” [10,12].

Moreover, Pb can be carried in water, either dissolved or as waterborne particles. However, a few compounds of Pb dissolve readily in water, though a significant amount is then precipitated and becomes incorporated into sediments at the base of the watercourse. The high concentration of Pb in this site might be attributed to the acid drainage from the indus-trial wastes and different chemical activities of hatcheries, fish processing, paint and ship repairing industries. The pres-ent study revealed that the Zn, Cu and Pb were much higher than the most quality guideline values (Table 4).

Among the sites, the highest mean concentration of Ni (77.5 µg/L) and Cr (15.3 µg/L) were observed in the water samples of the Sunderbans site which is attributed to the different industrial activities of stainless steel, ship breaking and repairing, rechargeable batteries, foundry products, jew-elry, metal ceramics, dyeing and leather industries, plating and gas turbine factories, export import zones in Khulna and Mongla port areas. Mostly, nickel is used in stainless steel which are characterized by strength, ductility, and resistance to corrosion and heat so that it is ideal for propeller shaft in boats and desalination plants.

Basically, Cr is used in stainless steel to give polished

silvery mirror coating, chrome plating, metallurgy to impart corrosion resistance, metal ceramics, shiny finish in dyes and paints, as a catalyst in dyeing and in the tanning of leather, to make molds for the firing of bricks and manufacture of magnetic tape. Chromium in water supplies is generally found in the hexavalent form which is highly toxic and in higher concentration to be carcinogenic [13]. We found the mean concentration of Ni and Cr were much higher than the toxicity reference value [14,15] (Table 4).

Arsenic forms a variety of inorganic and organic com-pounds of different toxicity reflecting the physical chemi-cal properties of arsenic at different valences. The highest mean concentration of As was observed at Chittagong ship breaking area (13.3 µg/L) which was higher than the WHO prescribed value for drinking water (Table 4). However, in coastal water, higher amount of arsenic comes mostly from the sediments deposited in the coastal sediment through the river system from the upland Himalayan catchments as well as the northern part of Bangladesh [16].

The highest Cd (0.09 µg/L) was observed in water at Cox’s Bazar site which might be attributed from different elec-troplating industries, ship repairing, and battery dumping. Besides, weathering of rocks, manures, municipal sewage sludge, fossil fuel combustion, artificial phosphate fertilizers [17,18] and pesticides also contribute significant amount of Cd in this area. Pesticides and fertilizers have been used in farming in Bangladesh since 1957. But since 1980, more fer-tilizers and pesticides were used to obtain more production

Table 4 Comparison of detected metal concentration (µg/L) in coastal water (n = 18) with guideline values along with some reported values in the literature.

Cr Ni Cu Zn As Cd Pb ReferencesMetal range (Cox. & Ctg.)

2.6−8.8 5.1−12.4 14.3−510 5.5−1390 2.3−13.3 0.006−0.09 0.4−109 (Present study)

Metal range (Sun. & Bhola)

11.8 −15.3 10.5−77.5 10.2−163 5−342 2.1−2.3 0.01−0.03 5.8−6.9 (Present study)

Quality of water *1. Limited 40 80 50 5 20 [44]2. No limited 20 60 25 2.5 10 [44]Drinking water 50 100 1000 50 5 50 [45]

11 52 9 150 2.2 2.5 [14]5 70 2000 10 3 10 [46]

* Imperative values (total metal) proposed by Andalusia Government (Spain)1. Limited = Tinto and Odiel point (river sites)2. No limited = Canal del Padre Santo point (Ría de Huelva estuary close to the Atlantic Ocean)DWSB = Drinking Water Standard for Bangladesh proposed through ECR (Department of Environment, DoE)USEPA = United States Environmental Protection AgencyTRV = Toxicity Reference ValueCox. = Cox's Bazar, Ctg. = Chittagong, Sun. = Sunderbans, Bhola = Meghna estuary

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in agricultural sector. Annually, approximately 45,172.43 metric tons of pesticides and 2,234,000 metric tons of fertilizers in 2009 were being used in this coastal area [9]. However, cadmium is produced as an impurity of phosphate fertilizers [19]. Cadmium content in phosphate rocks used as raw materials for phosphate fertilizer production which varies with the geographic origin and the type of rock [20]. Phosphate rock contains varying amounts of innate Cd and some of that Cd is transferred to fertilizer products during the manufacturing process [21].

Besides, CdSO4 is also frequently used in pesticide produc-tion [22]. Nevertheless, excessive use of phosphate fertilizers and pesticides in agricultural crop land are washed away to coastal water by rain and drainage. Though, there is no estimates of how much of the fertilizers and pesticides used find their way to the sea, but certainly a significant amount of pesticide and fertilizers contributes cadmium contamination in this area.

Statistical analyses were accomplished in order to eluci-date the relations among the metals and physical-chemical parameters in the water samples. Inter-metal interactions may illustrate the sources and pathways of the metals pres-ent in the particulate media. Pearson’s correlations among the metals and physical-chemical parameters were analyzed (p < 0.05 and p < 0.01) and shown in Table 5. The statisti-cal analysis has been done by excluding the extreme large value of Zn (1,390 µg/L) in the water sample of Cox’s Bazar Hatchery site (Table 3) due to avoid the large influence on existence and to show the stability and robustness of those analyses. The large value of Zn somewhat influence the Pearson correlation coefficient matrix for some trace metals

acting as outlier (conformed by box and whisker plot test in SPSS v22) that is notably different from the rest of the data. Therefore, it was important to consider the exclusion of aforesaid outlier within this distribution, because they already altered the results of the data analysis. However, the analysis was revealed the following relationships: Cu and As were positively correlated with salinity whereas Cr and Ni were positively correlated with suspended solids (SS). Re-markably, no correlations between pH and Temp. with total metal concentrations were observed. Comparing Inter-metal interactions, Cr showed a positive correlation with Ni, Cd and Pb. Besides, Zn showed a significant correlation with Cd while Cd also positively correlated with Pb. Negative corre-lation for pH with Temp. (r (x, y) = −0.542) and with salinity (r (x, y) = −0.568) was found. Higher correlation coefficient between the metals indicated identical sources, mutual de-pendence and identical behavior during their transport in the water [23] while negative correlation showing a non-identical behavior of these metals in coastal environment [24].

Concentration of trace metals in sedimentEstuaries are zones of complex interaction between fluvial

and marine process that act as geochemical trap for heavy metals bonded in the fine grained sediments; also, estuarine mixing leads to a depositional acceleration of clay mineral due to salinity change, favoring the entrapment and accumu-lation of metal adsorbed on clay particles [25,26]. The total metal concentration and total organic carbon (TOC) (%) in coastal surface sediments samples are shown in Table 6. The concentration ranges of trace metals and TOC (%) in coastal sediment samples were as follows: Cr: 10.7 − 57.8; Zn: 15.4

Table 5 Pearson correlation coefficient matrix for trace metals and physicochemical parameter in water samples (n = 18).pH Temp. Salinity SS Cr Ni Cu Zn As Cd Pb

pH 1Temp. –0.542* 1Salinity –0.568* 0.107 1SS 0.165 0.211 –0.483* 1Cr 0.228 0.100 –0.340 0.630** 1Ni –0.096 0.147 –0.198 0.689** 0.577* 1Cu –0.019 –0.378 0.489* 0.019 –0.069 0.311 1Zn –0.437 0.049 0.181 –0.173 –0.100 0.298 0.045 1As –0.437 0.321 0.618** –0.239 –0.402 –0.152 0.299 0.378 1Cd –0.187 –0.007 0.427 –0.057 0.523* 0.257 0.281 0.503* 0.141 1Pb 0.031 –0.166 0.350 –0.155 0.549* 0.043 0.186 –0.121 –0.021 0.923** 1* Correlation is significant at the 0.05 level (2-tailed).** Correlation is significant at the 0.01 level (2-tailed).

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− 58.9; Pb: 6.2 − 56.3; Ni: 10.4 − 38.0; Cu: 2.4 − 36.5; As: 1.5 − 5.0; Cd: 0.003 − 0.082 (mg/kg-dw) and TOC: 0.01 − 0.98 (%), respectively. The mean concentrations of studied met-als in coastal sediment samples followed a decreasing order of Zn > Cr > Pb > Ni > Cu > As > Cd. Interestingly, most of the studied metals except As and Cd showed the highest mean concentration at Chittagong ship breaking area while the samples of Cox’s Bazar showed the lowest concentration except for As.

However, among the sites, the highest mean concentra-

tion of Cr (55.8 mg/kg-dw) was observed at Chittagong ship breaking area which exceeded the sediment quality guide-line values (Table 7). The Cr enrichment of sediment could have been caused by two reasons: i) natural: concentration of Cr bearing minerals and ii) anthropogenic: different types of industrial activities such as stainless steel, ship breaking and repairing, metal ceramics, textile, dyeing and leather industries (tanneries) discharging chromates and dichromate being used as oxidants. The highest concentration was at-tributed due to enormous activities of dismantling of large

Table 6 Total metal concentrations (mg/kg-dw) and TOC (%) in sediment samples (n = 18).Sampling sites Stations Cr Ni Cu Zn As Cd Pb TOC

(%)St. 1. (a) Cox’s Bazar Bakkhali estuary

1 29.6 31.1 17.2 45.2 2.4 0.024 28.3 0.672 32.8 36.0 17.3 48.3 3.0 0.022 38.9 0.613 11.2 10.4 5.7 16.6 1.6 0.006 6.2 0.06

St. 1. (b) Cox’s Bazar Hatchery

1 18.0 27.0 4.3 24.8 5.0 0.004 9.4 0.052 10.7 16.1 2.6 15.4 3.6 0.003 6.9 0.043 12.0 16.6 2.4 18.5 3.9 0.003 7.6 0.02

St. 2. (a) Chittagong port

1 33.5 33.9 21.4 48.5 2.0 0.038 34.6 0.482 33.1 34.3 22.3 49.4 2.0 0.040 38.5 0.433 32.3 35.1 20.8 47.9 3.7 0.042 41.0 0.61

St. 2. (b) Chittagong ship breaking

1 51.8 37.9 36.5 58.9 2.5 0.054 56.3 0.612 57.8 38.0 31.2 56.3 2.2 0.051 49.7 0.543 55.8 36.7 28.3 54.2 2.0 0.045 40.6 0.46

St. 3. Sunderbans 1 26.4 23.7 24.5 43.6 2.6 0.059 27.1 0.822 26.7 24.0 26.7 45.2 2.6 0.082 32.0 0.983 26.2 23.7 25.7 45.2 2.8 0.068 25.9 0.85

St. 4. Meghna estuary Bhola

1 25.0 27.5 19.5 37.3 2.4 0.053 23.2 0.192 24.2 24.4 15.8 35.2 1.7 0.037 16.2 0.143 20.0 20.7 9.7 31.5 1.5 0.019 7.8 0.01

Table 7 Comparison of detected metal concentration (mg/kg-dw) in coastal sediments with some guideline values along with a reported value in Bangladeshi river.

Cr Ni Cu Zn As Cd Pb ReferencesCoastal area in Bangladesh

11−58 10−38 2−37 15−59 1.5−5 0.036−0.082 6−56 Present study

Guideline value 52.3 15.9 18.7 124 7.24 0.7 30.2 ISQGa

Guideline value 26 16 16 120 6 0.6 31 TRVb

Guideline value 26 16 16 120 6 0.6 31 LELc

Guideline value 110 75 110 270 33 10 250 SELd

Mouth of Karnafully River, Bangladesh

78.1 - 32.9 33.5 - 0.88 23.2 [29]

a: Interim Marine Sediment Quality Guidelines [47]b: Toxicity Reference Value proposed by USEPA [14]c: Lowest Effect Level and d: Severe Effect Level [48]

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ship which carry huge amount of Cr bearing materials such as painting, anti-corrosive materials, chromium alloy, waste disposal of various refuse materials lubricants, oil residue and floatable grease ball. Besides, heavy industries like steel and rerolling engineering along the coast also contributes huge Cr discharge in this area [27,28]. Zinc is one of the earliest known trace metals.

The highest mean concentration of Zn (54.2 mg/kg-dw) was also found at Chittagong ship breaking area. It’s varia-tion in concentration depended on characteristics of the sedi-ments. The extensive uncontrolled ship breaking and other industrial activities probably enhanced the concentration of Zn [29]. Salomons and Forstner [30], GESAMP [31] reported that coastal marine sediment of Bangladesh showed higher Zn concentration than the marine sediment from other parts of the world [27].

A significant variation was observed for Pb in sediment samples, which might be related to Pb sources and sediment characteristics. Considering Pb, among the sites, the high-est mean concentration was recorded as 40.6 mg/kg-dw at Chittagong ship breaking area which exceed the Sediment quality Guideline values (Table 7). High amount of Pb was observed due to contribution of Pb smelting factories, auto-mobile industries, ship breaking activities and various an-thropogenic intrusions. Nevertheless, some Pb compounds dissolve freely in water while most of them are incorporated in the sediments at the base of the watercourse [32]. At Chit-tagong ship breaking area, the highest mean value of Ni was found (36.7 mg/kg-dw) which was two times higher than the ISQG values (15.9 mg/kg-dw) (Table 7).

Nickel concentration in sediment showed higher value that might be the geochemical trap for Ni bonded in the fine grained sediment; depositional acceleration of clay mineral and accumulation of Ni adsorbed on clay particles. More-over, huge industrial activities of stainless steel, plating and gas turbine factories, foundry products, jewelry, atmospheric emission, leachates from defused Ni-Cd and other recharge-able batteries by the ship breaking and repairing activities contributed excessive Ni in this area [33].

Copper was intimately related to the aerobic degradation of organic matter [34]. Copper distribution in the study area was very complex in nature. The concentration of Cu did not follow any regular pattern of distribution [27]. The con-centration of Cu ranged from 2.4 to 36.5 mg/kg-dw. Among the sites, the highest mean concentration of Cu was recorded as 28.3 mg/kg-dw at Chittagong ship breaking area which exceeded the ISQG values (18.7 mg/kg-dw).

Among the sites, the highest mean concentration of As

was observed as 4.2 mg/kg-dw at Cox’s Bazar hatchery site which did not exceed the Sediment quality Guideline values. High As concentration might be attributed to the anthropo-genic activities such as treatment of agricultural land with fertilizers and arsenical pesticides [35,36], treating of wood by using copper arsenate [37,38].

The highest mean concentration of Cd was recorded as 0.07 mg/kg-dw at Chittagong ship breaking area which might be attributed to the runoff of Cd containing phosphate fertilizer from agricultural areas [39], dismantling of old ship and discharge of untreated sewage effluents [40], local fishing and other anthropogenic activities along the coast area [29,41].

The composition of the total organic carbon in sediment samples varied among the sites due to its origin in the aquatic environment. The TOC (%) in sediments ranged from 0.01 to 0.98 (Table 6). The highest percentage of organic carbon was observed in Sunderbans site (0.98) which might be attributed to the high input of organic matter from the Sunderbans for-est and huge industrial activities of Khulna and Mongla port areas. It is well established that natural organic matter has a high affinity through adsorption or complexation for heavy metals in the aquatic environment [42]. As a consequence, it affects the eco-toxicity, environmental transfer and geo-chemical behavior of trace metals in the aquatic environ-ment. The coupling between the cycles of TOC and trace metals is ultimately reflected in the chemical composition of marine sediments [43].

Statistical analyses were performed in order to elucidate the associations among the metals and TOC in the sediment samples. Inter-metal interactions may illustrate the sources and pathways of the metals present in the particulate media. Pearson’s correlations among the metals and TOC were analyzed (p < 0.05 and p < 0.01) and are depicted in Table 8 which showed the following relationships: Cr was signifi-cantly correlated with most of the analyzed trace metals and TOC except As. Moreover, TOC was positively correlated with all of the analyzed metals except As. Besides, Ni was positively correlated with Cu, Zn, Pb and TOC. The Cu contents were also positively correlated with Cu, Zn, Cd, Pb and TOC. The Zn contents were significantly correlated with Cr, Ni, Cu, Cd, Pb and TOC. Cd was correlated with Cr, Cu, Zn, Pb and TOC. Higher correlation coefficient between the metals indicated identical sources or common sink, mutual dependence and identical behavior during their transport in the sediments [23]. Although in this study, it is difficult to conclude specifically the identical sources of metal dis-tribution considering different sampling sites in the same

Journal of Water and Environment Technology, Vol. 14, No. 4, 2016 257

coastal area. In fact, Bangladesh is a downstream riverine country with more than 230 rivers receiving huge industrial effluents from neighboring country as well as inland sources dumping up through the Bhola estuary to the Bay of Bengal. Besides, there are approximately 8,542 industrials establish-ments dealing with different kind of industrial activities in the coastal area which also release all untreated industrial effluents directly to the Bay of Bengal [9]. In this sense, we can consider the whole coastal area of the Bay of Bengal as a single watershed while we don’t have reliable data regarding the real sources and how much the sources contribute pollu-tion in the coastal area. Interestingly, for As, no correlation was observed among the analyzed metals and TOC suggest-ing it’s source or conservative behavior is not identical to the other metals in this coastal environment [24,28].

CONCLUSIONS

This study was developed to provide base line informa-tion on some toxic trace metals concentration in different coastal environmental media of Bangladesh. The water of Cox’s Bazaar hatchery site was more polluted where elevated concentration of Zn, Cu and Pb were observed. Interestingly, high concentration of As was observed in Chittagong ship breaking area. Metal concentrations in sediment were also very high in Chittagong ship breaking area. Metal concentra-tions were compared with quality guidelines values and they were exceeded sometimes for water, fishes and frequently for sediments. The elevated level of trace metals in this Ban-gladeshi coastal ecosystem which should not be ignored and immediate control measure is recommended.

ACKNOWLEDGEMENT

The authors would like to acknowledge to the Graduate School of Environment and Information Sciences, Yoko-hama National University, Japan for providing research grant through the International Environmental Leadership Program in Sustainable Living with Environmental Risk (SLER) and through research cooperation program for Ph.D students. The authors also thankfully acknowledge to the Yokohama Plant Protection authority of Japan for the im-port permission of the sediment samples from Bangladesh (MAFF Directive Import Permit No. 25Y324, Date of Issue: June 11, 2013).

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