Study area and sampling location: Four sampling sites (Cox’s Bazar, Chittagong, Meghna Estuary, and Sunderbans) with three different locations of each were investigated in the southeast and southwest coastal area of Bangladesh. The first site (St 1)is located at the southeast coastal area in Cox’s Bazaar which lies between 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 unbroken125 km world’s longest natural sandy sea beach. Coastal shrimp culture has been widely practiced on this coast for a couple of decades where more than 53 shrimp hatcheries and aquafarms, big fish landing centers can be found in very close relation to the sea beach. Besides, these sampling areas were mostly influenced by un-planned industries, huge hotels for tourists, and municipal sewage. The second site (St 2) is located near the Chittagong port and shipbreaking area which lies between latitudes 22° 13′27′′N to 22°38′22′′N and longitudes 91° 48′14′′Eto91°32′45′′E. This is the southeastern principal seaport region of the country, straddling the hills at the estuary of the Karnaphuli River which is regarded as industrial and commercial hubs. There are more than 8542 industrial establishments dealing with cement clinker, fertilizers, steel rerolling, paper and pulp, rubber and plastic, oil refinery, beverages, sugar, pharmaceuticals, tobacco, jute, textiles, fish processing, tannery, paint, rechargeable batteries, jewelry, plating, automobile engine, electronic industries, and shipbreaking yard (BOBLME,2011). The third site (St3) is located near the Meghna Estuary 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 the country and trans-boundary countries. The last site (St 4) is located near the southwest part of the coastal area of Sundarbans that is regarded as a large mangrove ecosystem in Bangladesh which lies between latitudes 22° 34′43′′N to 22°18′02′′N and longitudes 89° 32′48′′Eto89°36′26′′E. This sampling area is also mostly influenced by different industrial activities like cement factories, export processing zone, seaports, paper industries, oil refinery industries, steel rerolling, fertilizer industry, hatcheries, aquafarms, fish processing industries, leather industries, dyeing industries, and paint industries. Sample collection and preparation: Three mostly consumed fish (Hilsa (Tenualosa ilisha), Rupchanda (Pampus argentius), Long tongue sole (Cynoglossus lingua)) and crustacean species (Indian shrimp (Penaeus indicus) and Mudcrab (Scylla serrata)) were collected from the sampling sites. Immediately after collection, fish and crustacean samples were kept in an airtight insulating box and thereafter transported to the laboratory of the Department of Fisheries, University of Dhaka, Bangladesh.After transportation, fish and crustaceans samples were rinsed in deionized water to remove surface adherents. None edible parts were removed with the help of a steam cleaned stainless steel knife. The edible portion of the samples was cut into small pieces. A composite of at least 9 samples of each fish and crabs, and 18 for shrimps was prepared and homogenized in a food processor and 100 g test portions were stored at −20 °C in the Laboratory of Fisheries Department, Dhaka University. Then, all samples were freeze-dried for 48 h until a constant weight was attained. All processed samples were brought to Yokohama National University, Japan, for chemical analysis under the permission of Yokohama Plant Protection Station. Sample digestion and metal extraction A 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 polytetrafluoroethylene (PTFE) digestion vessels and poly-propylene containers were cleaned, soaked in 5 % HNO3 for more than 24 h, then rinsed with Milli-Q water and dried. For metal analysis, 0.2 g of fish and crustaceans samples of each were treated with 5 mL 69 % HNO3 acid (Kanto Chemical Co., Tokyo, Japan) and 2 mL 30 % H2O2 (Wako Chemical Co., Tokyo, Japan) in closed digestion vessels. After mixing for 20 min, the vessels containing samples were placed in a microwave digestion system (Berghof-MWS2, Berghofspeedwave®, 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 the last step 10 min at 100 °C with 400 W.After digestion, acid solutions with samples were transferred into a Teflon graduated cylinder and the total volume was made up to 50 mL with Milli-Q water. The digested acid solutions were then filtered by using a syringe filter (DISMIC®-25HPPTFE, pore size=0.45μm; Toyo Roshi Kaisha, Ltd., Tokyo Japan) and stored in 50 mL polypropylene tubes (Nalgene, NY, USA). Instrumental analysis: For trace metals, samples were analyzed using an inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7700 series, USA, Table1). Multi-element Standard XSTC-13 (SPEX CertiPrep®, USA) solutions were used to prepare a calibration curve. The calibration curves withR2>0.999 were accepted for concentration calculation. Before starting the sequence, relative standard deviation (RSD<5 %) was checked by using tuning solution (1μg/L each of Li, Y, Ce, Tl, Mg, and Co in 2 wt % HNO3) purchased from Agilent Technologies.Internal calibration standard solution containing 1.0 mg/Leach of beryllium (Be) and tellurium (Te), and 0.5 mg/L each of indium (In), yttrium (Y), cobalt (Co), and thallium (TI) were purchased from SPEX CertiPrep®, USA, and it was added into each sample. Working standards (0, 10, 20, 50, and100μg/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 was quantified by calibration based on internal standards.Quality control and quality assurance The quality of total acid digestion of the fish and crustaceans was checked by using a certified reference material (NMIJCRM 7402-a, Codfish tissue) purchased from the National Institute of Advanced Industrial Science and Technology (AIST) and yielded a good accuracy of the analysis. The 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.