Introduction

The increasing usage of heavy metals in industry has led to serious environmental pollution through effluents and emanations during the past several decades (Sericano et al. 1995). Subsequently, these activities have increased the release of harmful heavy metals into the aquatic environment (Agusa et al. 2005, 2007; Hajeb et al. 2009) which are well known environmental pollutants (Gulec et al. 2004). Heavy metals are a global concern, due to their potential toxic effect and ability to bioaccumulate in aquatic ecosystems (David et al. 2012; Hall 2014; Batvari et al. 2015). Pb, Ba, Cd, Hg, Cr, and As are classified as toxic heavy metals, and maximum residual levels have been prescribed for humans (FAO 1983; EC 2001; FDA 2001) and have no established role in biological system (Canli and Atli 2003), whereas metals such as Cu, Na, K, Ca, Mn, Se, Fe, and Zn are essential metals for fish metabolism but may also bioaccumulate and reach toxic levels that can potentially destroy the ecological environment (Agusa et al. 2005, 2007; Hajeb et al. 2009). The bioaccumulation of heavy metals in living organisms and biomagnifications describe the processes and pathways of pollutants from one trophic level to another. Heavy metals can enter the food web through direct consumption of water or organisms taken as food (zooplankton, phytoplankton, and faunal of the bottom) or by uptake through the gills and skin and be potentially accumulated in edible fish in aquatic ecosystem. The acidic conditions of aquatic environment might cause free divalent ions of many heavy metals to be absorbed by fish gills (Part et al. 1985).

Fish are widely used as bio-indicators of heavy metal contamination (Svobodova et al. 2004; Kuklina et al. 2013; Authman et al. 2015) because they occupy different tropic levels and are of different sizes and ages (Burger et al. 2002). Relationship between metal concentrations in fish and in the water has been studied in both field and laboratories (Linde et al. 1996; Moiseenko et al. 1995; Zhou et al. 1998).

Fish, shellfish, and other aquatic organisms constitute a large part of daily meal of human population in countries like Bangladesh. Consumption of heavy metal-contaminated fish for prolonged period results in accumulation of heavy metals in human.

The river Buriganga runs by the side of the Dhaka City, the capital of Bangladesh, which is a megacity of about 12 million people. City dwellers largely depend on the Buriganga River for sources of domestic water supply. It serves as major transportation route and flood control and drainage outlet and is used for agricultural, sanitary, and industrial purposes (Alam et al. 2002). Intensive human intervention, rapid industrialization, unplanned urbanization, and economic development have resulted in increased water pollution (Moniruzzaman et al. 2009). Earlier studies reported that the water flow (Ahmad et al. 2010) and ecological function of the Buriganga River (Yousuf et al. 2008) have been greatly influenced. The river is increasingly being polluted with the city’s thousands of industrial units and huge volumes of toxic wastes dumped by sewerage lines every day (Islam et al. 2006). The Department of Environment (DoE) identified 249 factories along the river Buriganga (Sarker 2005). However, the river Buriganga received continuously wide variety of heavy metals originating from industrial discharges, batteries, lead-based paint and gasoline discharge from cargo, launch and mechanized boat, traffic and improper domestic waste discharge, etc. The river Buriganga has become biologically and hydrologically dead due to indiscriminate dumping of domestic and industrial wastes and encroachment by unscrupulous people (Mahmud-ul-Islam 2011). Fish in Buriganga can also accumulate metals in its tissues through absorption, and humans can be exposed to these metals via the food web. Heavy metals, unlike organic pollutants, cannot be chemically degraded or biodegraded by microorganisms. Thus, their content has steadily increased in water and subsequently accumulated in sediments, plants, fishes, and even in humans (Che et al. 2006). The consumption of contaminated fish causes acute and chronic effects to humans (Nord et al. 2004). Although a number of studies have investigated heavy metal concentrations in fishes (Ahmad et al. 2010), water (Ahmad et al. 2010; Mohiuddin et al. 2011), and sediment (Ahmad et al. 2010; Mohiuddin et al. 2011) of the Buriganga River, no research has been conducted on profile of heavy metal in the fish species, crustacean (prawn), and shellfish (Mollusca) of the Buriganga River and evaluate the associated health risks. In this context, the present study was designed to determine the accumulation profile of heavy metals, namely V, Cr, Mn, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, and Pb, in fish species, crustacean (prawn), and shellfish (Mollusca) collected from the river Buriganga and evaluate their health risk for humans.

Materials and methods

Collection and preparation of samples

Samples were collected between August and September, 2013, from different stations of the river Buriganga near Kamrangirchar (Fig. 1) where fishing effort is high. Fish and prawn samples were collected from the professional fishermen while they were fishing in the river using different gears. Special care was taken to make sure that the species were of similar size and weight. The samples were put in plastic bag/containers and transported to the laboratory.

Fig. 1
figure 1

Map of sampling site

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The samples were immediately washed with care using clean tap water and the biological information of the collected samples was recorded (Table 1). The collected species were divided into three groups: (i) fish (Ailia coila, Gagata youssoufi, and Mastacembelus pancalus; (ii) crustaceans (prawn; M. rosenbergii); and (iii) shellfish (Mollusca; Gastropoda; snail; Indoplanorbis exustus). Whole bodies of the fish (including the bones), crustacean, and Mollusca were used for analyses. A composite sample for each species was prepared and homogenized in a stainless steel blender cup. Fifty-gram test portions were stored at −20 °C for analytical methods. The samples were then freeze dried and sealed in airtight plastic bag and transported to Japan for analytical methods. The metal contents were expressed as milligrams per kilogram wet weight of fresh fish, prawn, and Mollusca.

Table 1 The biological background information of fishes, crustacean, and shellfish
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Analytical methods

Reagents

All solutions were prepared with analytical reagent-grade chemicals and ultrapure water. SUPRAPUR® nitric acid (HNO3, 67 % (v/v)) was purchased from Kanto Chemical Co, Japan, and H2O2 was purchased from Wako Chemical Co, Japan. Standard stock solutions containing 10 mg/L of each element (Cd, As, Pb, Cr, Ni, Zn, Se, Cu, Mo, Mn, Sb, Ba, V, and Ag), and internal standard solutions containing 1.0 mg/L of indium (In), yttrium (Y), beryllium (Be), tellurium (Te), cobalt (Co), and titanium (Ti) were purchased from SPEXertificate® and were used to prepare calibration and internal standards. Working standards were prepared daily in 5 % (v/v) HNO3 at 67 % and were used without further purification. A solution of 10.0 mg/L multielement solution (Merck, Darmstadt, Germany) was used to prepare a tuning solution with several elements such as indium, uranium, barium, and lithium, capable of covering a wide range of masses. Ultra-pure grade carrier (Argon (Ar)) was supplied from Air Liquide (Japan).

Sample digestion

A microwave (Berghof Microwave MWS-2, Germany) was used in preparation of samples to analyze various metals with ICP-MS (Agilent 7700, USA). The microwave digestion system has been designed to perform chemical digestion under extreme pressure and temperature conditions in chemical laboratories. Digestion reagents included 5 mL HNO3 acid and 2 mL H2O2. The weighed samples of 0.2 g were then added into the digestion reagent in a DAP-60K type pressure vessels (Berghof, Germany) entirely made of tetrafluoromethoxylene (TFM). Three-step digestion procedure were followed: (1) temperature and power were maintained at 180 °C and 85 % respectively for 15 min, (2) temperature was kept steady at 200 °C for 15 min together with 90 % of the power, and (3) reduced temperature (100 °C) and power (40 %) were used for 10 min to cool down the Teflon vessels. After that, all Teflon vessels were kept in cold water to reduce the residual pressure inside the Teflon vessel. Samples were then transferred into a Teflon beaker, and total volume was made up to 25 mL for water and 50 mL for sediments with Milli-Q water (Elix UV5 and Milli-Q, Millipore, USA). The digest solution was then filtered (DISMIC®—25HP PTTF syringe filter (pore size = 0.45 mm) Toyo Roshi Kaisha, Ltd., Japan) and stored in a crew cap plastic tube. The samples were then subjected to analysis for various trace metals using ICP-MS followed by three times digestion for each sample. Afterwards, the vessels were cleaned by Milli-Q water and dried with air. Finally, two blank digestions with 5 mL HNO3 following the said digestion procedures were carried out to clean up the digestion vessels (Berghof’s product user manual).

Quality assurance

All test batches were evaluated using an internal quality approach and validated if they satisfied the defined internal quality controls (IQCs). For each experiment, a run included blank, certified reference materials (CRM) as internal standard in samples, and samples analyzed in duplicate to eliminate any batch-specific error. Multielement standard solution was used to prepare standard curve. Before starting the sequence, relative standard deviation (RSD, <5 %) was checked by using tuning solution purchased from Agilent company. Five standards with standard linear regression and internal standardization were prepared at levels ranging from 0 to 50 μg/L for Cd, As, Pb, Cr, Ni, Zn, Se, Cu, Mo, Mn, Sb, Ba, V, and Ag. The calibration curve was plotted from six points, including the calibration blank.

To ensure accuracy, precision, specificity, sensitivity, and linearity of the estimated values for food constituents, appropriate methods as given in the most recent edition of Official Methods of Analysis of AOAC International were selected. For some nutrients, modification of the AOAC Official Methods was needed. In such case, the ASEAN Manual of Nutrient Analysis (ASEANFOODS 2011) was considered to be useful for a list of methods adopted after method validation as per AOAC/IUPAC protocol in order to analyze the composite sample.

Each analytical procedure was accompanied with a quality assurance program to ensure the quality of the data. Extensive documentation of every single step for laboratory analysis was carried out. These documentations have been kept for data management and identification of missing steps and values, as well as recall points for repeats of analysis.

Statistical analysis

The data were statistically analyzed using the statistical package, SPSS 16.0 (SPSS, USA). The means and standard deviations of the metal concentrations in fish species were calculated. Multivariate post hoc Tukey tests were employed to examine the statistical significance of the differences among mean concentrations of trace metals among different fish species for each metal.

Health risk estimation

Target hazard quotient

The target hazard quotient (THQ) is an estimate of the risk level (non-carcinogenic) due to pollutant exposure. To estimate the human health risk from consuming metal-contaminated fish, the target hazard quotient (THQ) was calculated as per USEPA Region III Risk-Based Concentration Table (USEPA 2011). The equation used for estimating THQ was as follows:

$$ \mathrm{T}\mathrm{H}\mathrm{Q}=\frac{\mathrm{EF}\times \mathrm{E}\mathrm{D}\times \mathrm{FIR}\times \mathrm{C}\mathrm{f}\times \mathrm{C}\mathrm{M}}{\mathrm{WAB}\times \operatorname{ATn}\times \mathrm{R}\mathrm{f}\mathrm{D}}\times {10}^{-3} $$

where THQ is the target hazard quotient, EF is the exposure frequency (365 days/year), ED is the exposure duration (30 years for noncancer risk as used by USEPA 2011), FIR is the fish ingestion rate (49.5 g/person/day; BBS 2011), Cf is the conversion factor (00.208) to convert fresh weight (F w) to dry weight (D w) considering 79 % of moisture content in fish, CM is the heavy metal concentration in fish (mg/kg d.w.), WAB is the average body weight (bw) (70 kg), ATn is the average exposure time for noncarcinogens (EF × ED) (365 days/year for 30 years (i.e., ATn = 10,950 days) as used in characterizing noncancer risk (USEPA 2011), and RfD is the reference dose of the metal (an estimate of the daily exposure to which the human population may be continuously exposed over a lifetime without an appreciable risk of deleterious effects.)

Hazard index

The hazard index (HI) from THQs is expressed as the sum of the hazard quotients (USEPA 2011).

$$ \begin{array}{c}\hfill HI=THQ(V)+THQ(Cr)+THQ(Mn)+THQ(Ni)+THQ(Cu)+THQ(Zn)+THQ(As)+\hfill \\ {}\hfill THQ(Se)+THQ(Mo)+THQ(Ag)+THQ(Cd)+THQ(Sb)+THQ(Ba)+THQ(Pb)\hfill \end{array} $$

where HI is the hazard index, THQ (V) is the target hazard quotient for V intake, and so on.

Target cancer risk

Target cancer risk (TR) was used to indicate carcinogenic risks. The method to estimate TR is also provided in USEPA Region III Risk-Based Concentration Table (USEPA 2011). The model for estimating TR was shown as follows:

$$ \mathrm{T}\mathrm{R}=\frac{\mathrm{EF}\times \mathrm{E}\mathrm{D}\times \mathrm{FIR}\times \mathrm{C}\mathrm{F}\times \mathrm{C}\mathrm{M}\times \mathrm{C}\mathrm{PSo}}{\mathrm{WAB}\times \mathrm{A}\mathrm{T}\mathrm{c}}\times {10}^{-3} $$

where TR is the target cancer risk, CM is the metal concentration in fish (μg/g), FIR is the fish ingestion rate (g/day), CPSo is the carcinogenic potency slope, oral (mg/kg bw/day), and ATc is the averaging time, carcinogens (365 days/year for 70 year as used by USEPA 2011). Since CPSo values were known for Ni, AS, Cd, and Pb, so, TR values were calculated for intake of these metals.

Results and discussion

Concentration of heavy metals

Mean concentrations and standard deviation of heavy metals in freshwater fishes (A. coila, M. pancalus, and G. youssoufi), crustaceans (M. rosenbergii), and shellfish (Indoplanorbis exustus) are presented in Table 2. The heavy metals V, Cr, Mn, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, Sb, Ba, and Pb all recorded a 100 % incidence in fish, crustacean, and shellfish samples. Considerable variations were observed in the concentration of heavy metals among different species. This variation was due to the difference of feeding habits and accumulation capacities of the species.

Table 2 Mean (±SD) heavy metals concentration (mg/kg) in fishes, crustacean, and shellfish of the Buriganga River
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Mean V concentrations was as high as 1.84 ± 0.11 mg/kg in M. pancalus. The lowest V accumulation (0.17 ± 0.04 mg/kg) was in M. rosenbergii. Vanadium contents in the literature have been reported to be in the range of 0.047–1.310 mg/kg in dietary fish (Millour et al. 2012) and 0.054–0.274 mg/kg in fish (Guerin et al. 2011). Vanadium is an essential element for normal cell growth and essential component of some enzymes, particularly the vanadium nitrogenase used by some nitrogen-fixing microorganisms; it is beneficial for prevention of vascular diseases and also has therapeutic potentials for diabetics with a definite safe dose range because of its insulin-mimic effects. Vanadium complexes can reduce growth of cancer cells and improve human diabetes mellitus but can be toxic when present at higher concentrations. There is no maximum level established for dietary intake of V through fish consumption in the Bangladeshi legislation. The estimated daily upper boundary range of vanadium is 0.2 mg/day (USEPA 2011). Thus, the concentrations of V in all the samples were higher than the stipulated limit.

The concentrations of Cr in the fish, crustacean, and shellfish samples were in the range of 1.59 ± 0.93 to 16.05 ± 1.48 mg/kg. The lowest concentration, 1.59 ± 0.93 mg/kg, was measured in crustaceans while the highest concentration, 16.05 ± 1.48 mg/kg, was measured in shellfish (gastropod Mollusca). Among the fish species, the highest concentration was measured in M. pancalus (7.18 ± 1.38 mg/kg). This study indicated the higher concentration of Cr than the results observed by other authors in fish and Mollusca (bivalve) (Ahmed et al. 2009). These results suggest that there is dense Cr pollution. This might have resulted from the effluent coming from the tannery industries near the Buriganga River (Mohanta et al. 2010; Ahmad et al. 2010). Chromium concentration found in the present study was above the permissible limit of approximately 0.2 μg/g dry wt as recommended by FAO (1976). Concentration of Cr in fish and shrimp was reported to exceed the safe limit of FAO in an Indian river by Giri and Singh (2014). Several studies have shown that chromium (VI) compounds can increase risk of lung cancer (Ishikawa et al. 1994).

Concentrations of Mn were lower in all fish samples compared to prawn and shellfish. The lowest concentration of Mn (23.23 ± 0.56 mg/kg) was measured in G. youssoufi, while the highest concentration of Mn (319.66 ± 20.95 mg/kg) was measured in shellfish. Manganese concentrations in the present study were higher than those of several other studies. According to the previous literature, the Mn concentrations in the samples ranged from 0.54 to 79.08 μg/g (Bashir et al. 2013); the muscles of fishes found in Indian fish markets ranged from 0.14 to 3.36 μg/g (Sivaperumal et al. 2007). Manganese is an essential element for both animals and plants, and Mn deficiency results in severe skeletal and reproductive abnormalities in mammals (Sivaperumal et al. 2007).

The major source of Ni for humans is food and uptake from natural sources, as well as food processing (NAS-NRC National Academy of Sciences-National Research Council 1975). Increased incidence of cancer of the lung and nasal cavity caused by high intake of Ni has been also reported by workers in Ni smelters. Nickel was measured to be in relatively low concentrations in the investigated samples. The concentrations of Ni in the samples ranged from 0.36 ± 0.10 to 5.75 ± 2.40 mg/kg. The highest concentration, 5.75 ± 2.40 mg/kg, was measured in shellfish with the lowest detectable concentration, 0.36 ± 0.10 mg/kg, measured in A. coila. The estimated maximum guideline (USFDA 1993a, b, c) for Ni is 70–80 mg/kg. Thus, the concentrations of Ni in all the samples were far below the stipulated limit.

The concentration of Cu in prawn sample was extremely higher compared to the concentration of the other heavy metals that were analyzed in the fish, prawn, and shellfish samples. The concentrations of Cu in the samples analyzed ranged from 4.39 ± 0.49 to 575.34 ± 61.86 mg/kg, with the highest concentration, 575.34 ± 61.86 mg/kg, in prawn. However, the lowest concentration of 4.39 ± 0.49 mg/kg measured in G. youssoufi was far below the FAO guideline of 30 mg/kg. Thus, the concentrations of Cu in the fish and shellfish samples analyzed were all below the FAO recommended guideline (FAO 1983) except in prawn samples. Cu is an essential element that is carefully regulated by physiological mechanisms in most organisms (Erdoĝrul and Ates 2006). However, it poses potential hazards that endanger both animal and human health. Copper can be found in a natural environment and is essential for the normal growth and metabolism of all living organisms (Eisler 1998). However, it becomes toxic at high concentrations. Copper concentration in humans can increase by consuming contaminated fishes. The enrichment of Cu in macrobenthic fauna which may be due to the surrounding industrial activities input of Cu in water and sediments. Miramand and Bentley (1992) stated that Cu accumulated in the species due to the industrial activities in that area.

Zinc, an essential micronutrient for both animals and humans, has been a cofactor for nearly 300 enzymes in all marine organisms. As a constituent of many enzymes, Zn is responsible for certain biological functions, for which a relatively high level is required to maintain them. In the present study, Zn was found in all samples of fishes, crustacean, and shellfish. The highest concentration of 187.04 ± 9.79 mg/kg Zn was measured in prawn, while the lowest concentration, 58.56 ± 4.12 mg/kg, was in gastropod Mollusca. The FAO maximum guideline for Zn is 30 mg/kg (FAO 1983). The concentrations of Zn in the present study are higher than the guideline values. Therefore, these metals have posed threat through consumption of these organisms. Toxicity due to excessive intake of Zn has been reported to cause electrolyte imbalance, nausea, anemia, and lethargy (Prasad 1984).

Arsenic is present in our food in different chemical forms, but inorganic arsenic is more toxic than organic arsenic. It is difficult to reliably measure the forms of arsenic that are present. Inorganic arsenic is estimated to be 10 % of total arsenic (USFDA 1993a, b, c). In the present study, the total arsenic concentrations were estimated. The results showed a higher As concentration in the prawn followed by in Mollusca and fishes, M. pancalus, A. coila, and G. youssoufi (Table 2). The arsenic value in fish from the Buriganga River is higher than the concentration from an earlier report by Begum et al. (2013). Maximum allowable level of arsenic contaminants in fish, shellfish, and crustaceans are 2, 1, and 2 mg/kg, respectively (FSANZ Food Standards Australia New Zealand 2008). Thus, our result indicated that the As concentration is still below from the maximum allowable level of arsenic recommended by FSANZ (Food Standards Australia New Zealand 2008). However, recent research has suggested that As acts as an endocrine disruptor at extremely low concentrations (Stoica et al. 2000). Chronic exposure to inorganic arsenic may give rise to several health effects, including to the gastrointestinal tract, respiratory tract, skin, liver, cardiovascular system, hematopoietic system, and nervous system (Mandal and Suzuki 2002). Furthermore, an acute high level exposure to arsenic can lead to vomiting, diarrhea, anemia, liver damage, and death. Long-term (chronic) exposure is thought to be linked to skin disease, hypertension, some forms of diabetes, and cancer (Centeno et al. 2005).

Although Se is an essential micronutrient, it can be toxic at high levels (Coyle et al. 1993). A concentration of about 1 μg/g (wet weight) in prey is the threshold for Se toxicity in some fish, while muscle concentration of 2.6 μg/g (wet weight) is associated with adverse in the fish themselves (Lemly 1993a, b). However, the highest mean selenium concentration was observed in A. coila 1.99 ± 0.11 mg/kg followed by prawn (1.83 ± 0.0.60 mg/kg), the M. pancalus (1.71 ± 0.0.54 mg/kg), G. youssoufi (1.46 ± 0.54 mg/kg), and Mollusca (0.76 ± 0.53 mg/kg) (Table 2.). Selenium concentrations were elevated compared to Se concentrations reported for organisms from uncontaminated environments (0.5–4 mg/g dry mass) (Bebbington et al. 1977). Burger and Gochfeld (2005) estimated concentrations of selenium in small and large shrimp ranged from 0.14–0.16 and 0.19–0.23 μg/g, wet weight, respectively. These were lower than that of the present study; hence, the mean in Penaeus spp. was recorded as 2.4 μg/g with averages (1.0–2.7 μg/g). The recommended maximum permissible level of Se in drinking water is 0.01 ppm (UNEP/WHO 1988) and maximum permitted concentration 1.0 μg/g (NSW Health Department 2001 SHPN: (FB) 990198 ISBN: 0 7347 3109 4), 5 μg/g dry mass, Australia New Zealand Food Authority (ANFA 1992), so that all sampled had concentrations above the maximum recommended limits.

Molybdenum is an essential element in human nutrition. It is involved in many important biological processes, possibly including development of the nervous system, waste processing in the kidneys, and energy production in cells, but its precise function and interactions with other chemicals in the body are not well understood. Some evidence suggests that too little Mo in the diet may be responsible for some health problems. Dosages of more than 15 mg may be toxic, and excess molybdenum in the body can interfere with the metabolism of copper in the body; can give symptoms of gout; and may cause diarrhea, anemia, and slow growth. Mean Mo concentrations were 0.06 ± 0.00, 0.03 ± 0.00, 0.11 ± 0.00, 0.15 ± 0.00, and 0.24 ± 0.01 mg/kg in A. coila, G. youssoufi, M. pancalus, M. rosenbergii, and Indoplanorbis exustus, respectively. Higher concentration of Mo was measured in shellfish followed by prawn and fishes in the present study. In the literature, molybdenum levels have been reported to be in the range of 0.006–3.07 mg/kg in fish and shellfish samples (Noël et al. 2012). There is no maximum Mo level established for dietary intake of fish consumption in the Bangladeshi legislation. The recommended maximum Mo level permitted through food consumption is 2 mg/day (NAS-NRC National Academy of Sciences-National Research Council 2001). Therefore, molybdenum level in fish samples was within safe limits.

The concentration of Ag in all sample was extremely lower compared to the concentration of the other heavy metals that were analyzed in the fish, prawn, and shellfish samples. It was thought that the fish did not accumulate the Ag from the food since the fish had less Ag per unit weight; no biomagnification occurred (Terhaar et al. 1977). Bard et al. (1976) also discussed this lack of biomagnification in fish. Whole fish analyses gave 34 μg/kg in alewife and 39 μg/kg in rainbow smelt (Copeland et al. 1973). The result showed that mean Ag concentrations were 0.060 ± 0.00, 0.01 ± 0.00, 0.01 ± 0.00, 0.39 ± 0.08, and 0.01 ± 0.00 mg/kg in A. coila, G. youssoufi, M. pancalus, M. rosenbergii, and Indoplanorbis exustus, respectively.

Cadmium is a serious contaminant, a highly toxic element, which is transported in the air. The mean concentration of Cd in the shellfish (0.05 ± 0.00 mg/kg) and fishes (0.01 ± 0.00 to 0.02 ± 0.00 mg/kg) were found to be low but high in crustaceans (1.51 ± 0.04 mg/kg). The lowest mean concentration of cadmium is in G. youssoufi and M. pancalus. Şirelil et al. (2006) measured much lower concentrations of Cd than the current study, in vacuum packaged smoked fish species (mackerel, Salmo salar and Oncorhynchus mykiss), which varied from 0.003 to 0.036 mg/kg with a mean of 0.01367 mg/kg. Ashraf (2006) studied 57 samples of canned tuna fish and found the concentration of Cd ranged between 0.08 and 0.66 mg/kg which is much higher than the present findings. Ahmed et al. (2009) investigated the heavy metal concentration in fish and oyster from the Shitalakhya River, Bangladesh, and found seasonal variation of Cd, ranged from 1.09 to 1.21 mg/kg. Shellfish can be high in Cd (Gray et al. 2005; WHO 1992). The level of contamination of fish with Cd is largely affected by environmental pollution. An example of such an impact is a high concentration of the element (from 0.38 to 0.44 mg/kg) in the muscles of roach, bream, and perch from the drainage area of the Oława River (Dobicki 1990). The values were higher than the acceptable limit for Cd in fish (0.05 mg/kg). None of the investigated samples of fish and shellfish (2.00 mg/kg) in this study exceeded acceptable values for cadmium (FSANZ Food Standards Australia New Zealand 2008). The muscles of roach, bream, whitefish, perch, and pike from Danish lakes did not pose any threat to humans in terms of contamination with cadmium (0.0 mg/kg–0.045 mg/kg) (Andersen et al. 1986). Cadmium occurs naturally in low levels in the environment and is also used in batteries, pigments, and metal coatings. Industrial processes such as smelting or electroplating and the addition of fertilizers can increase the concentration of Cd in the Buriganga River (environment). Long-term or high dose exposure to cadmium can cause kidney failure and softening of bones (Vannoort and Thomson 2006), and high levels of cadmium have been linked to prostate cancer (Gray et al. 2005).

Antimony has received increasing attention recently due to its toxicity and potential human carcinogenicity. Antimony is a natural element, with an average natural abundance in the earth’s crust and seawater of approximately 0.2 mg Sb/kg and 0.24 μg Sb/L, respectively (Lide 2009). In the present study, Sb concentrations were measured to be lower in all samples. The highest mean concentration was measured in M. pancalus 0.04 ± 0.00 mg/kg followed by Mollusca (0.03 ± 0.00 mg/kg), prawn (0.02 ± 0.00 mg/kg), and G. youssoufi (0.01 ± 0.00 mg/kg) and A. coilia (0.01 ± 0.00 mg/kg). The recommended maximum permissible level of Sb in freshwater prawn (Macrobrachium caledonicum) was 1.00 mg/kg (ANZFA 1996, 2000). All sampled had concentrations far below the maximum recommended limits. Due to their natural occurrence, biota will naturally accumulate metals at least to some degree without deleterious effect (ICMM 2007).

Small amounts of water-soluble Ba may cause a person to experience breathing difficulties; increased blood pressures; heart rhythm changes; stomach irritation; muscle weakness; changes in nerve reflexes; swelling of the brains; and liver, kidney, and heart damage. Mean barium concentrations were 2.38 ± 0.08, 6.87 ± 0.11, 5.44 ± 0.08, 22.72 ± 1.00, and 49.89 ± 0.92 mg/kg in A. coila, G. youssoufi, M. pancalus, M. rosenbergii, and Indoplanorbis exustus, respectively. Barium contents in the literature have been reported to be in the range of 0.000–0.945 mg/kg in dietary fish (Millour et al. 2012). There is no maximum Ba level established for dietary intake of fish consumption in the Bangladeshi legislation. The maximum tolerable daily intake recommended by the Scientific Committee on Health and Environmental Risks as 12 mg/day (SCHER Scientific Committee on Health and Environmental Risks 2012).

The mean values of Pb were 0.47 ± 0.03 mg/kg in A. coila, 0.54 ± 0.01 mg/kg in G. youssoufi, 3.17 ± 0.07 mg/kg in M. pancalus, 0.51 ± 0.01 mg/kg in M. rosenbergii, and 4.55 ± 0.11 mg/kg in Indoplanorbis exustus. The highest concentrations of lead were found to be 4.55 ± 0.11 mg/kg in Indoplanorbis exustus, and the lowest lead concentrations were measured to be 0.47 ± 0.03 mg/kg in A. coila. Ahmad et al. (2010) reported more Pb in chapila fish (13.52 mg/kg) from the Buriganga River. It was apparent that the samples of fishes, prawn (crustaceans), and Mollusca (shellfish) were bottom living; therefore, sediments could be the major source of Pb contamination in those organisms. In addition, Pb is a ubiquitous pollutant which could find its way into the Buriganga River through discharge of industrial effluents from various industries such as printing, dyeing, oil refineries, textile around Dhaka City, and other sources. Maximum allowable level of Pb contaminants in fish, and shellfish are 0.5 and 1 mg/kg, respectively (FSANZ Food Standards Australia New Zealand 2008). The fact that toxic metals are present at high concentrations in fish is of particular importance in relation to the (FAO/WHO 1976) standards for Pb. The maximum permissible doses for an adult are 3 mg Pb per week, but the recommended doses are only one-fifth of those quantities FAO/WHO.

Most of the metals were in high concentrations compared to the limits for fish, prawn, and Mollusca proposed by FAO, WHO, FSANZ, etc. although the heavy metal accumulation was lower in fishes compared to prawn and shellfish. These data provide a useful baseline to measure any future changes in local pollution.

Health risk estimation

The health risk assessments are based on assumptions. The risk associated with the carcinogenic effects of target metal is expressed as the excess probability of contracting cancer over a lifetime of 70 years. The target hazard quotient (THQ) estimated for individual heavy metals through consumption of different fish species is presented in Table 3. The acceptable guideline value for THQ is 1 (USEPA 2011). THQ values were less than 1 for all individual heavy metal in all three fish species indicating no non-carcinogenic health risk from ingestion of a single heavy metal through consumption of these fishes. The highest THQ value was estimated for Cr (0.35) followed by Cu (0.34) contaminated in M. pancalus. Although the THQs for single metal ingestion were within the acceptable limit, the combined impacts of all metals under consideration were near the acceptable limit of 1. Cu, Cr, As, and Zn contributed the most in the HI in all three fish species (Fig. 2). M. pancalus showed the highest health risk among three fish species. The HI for M. pancalus was 1.03 while it was 0.51 and 0.44 for A. coila and G. youssoufi, respectively (Table 3). This indicates that continuous and excessive intake of this fish especially M. pancalus could result in chronic non-carcinogenic effect. The TR values were estimated for the metals reported with known carcinogenic effects. The TR values for Ni, As, Cd, and Pb ranged from 2.83E−06 to 84.33E−04 in A. coila, 3.25E−06 to 5.41E−04 in G. youssoufi, and 1.91E−05 to 1.92E−03 in M. pancalus, respectively (Table 4).

Table 3 Target hazard quotient (THQ) for different heavy metals and their hazard index (HI) from consumption of three fish species collected from the Buriganga River
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Fig. 2
figure 2

Composition of hazard index (HI) for different heavy metals from consumption of three fish species collected from the Buriganga River

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Table 4 Target cancer risk (TR) of heavy metals from consumption of three fish species collected from the Buriganga River
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This indicates that excessive consumption over a long time period might cause carcinogenic effect as the TR values were higher than the acceptable guideline value of 10−6 (USEPA 2011). Although the fish species under the present study were found safe for human consumption, the probability of contracting cancer is present for continuous consumption for 70 years.

Conclusion

The present study concludes that different fish species, prawn, and shellfish collected from river Buriganga accumulates various metals at concentrations more than the maximum permissible limits. Although, at current concentrations in fish, prawn, and shellfish, no metal was found to pose potential non-carcinogenic health risk individually, but collectively, the metals were found enough to be considered as potential human health hazard. People who continuously consume fish contaminated with metals as found in the present study are under the target cancer risk in the long run.