Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv Seasonal variations of trace metals from water and sediment samples in the northern Bay of Bengal Md. Solaiman Hossain a,b,∗ , Md. Kawser Ahmed a , Subrata Sarker b , M. Safur Rahman c a Department of Oceanography, University of Dhaka, Dhaka 1000, Bangladesh b Department of Oceanography, Shahjalal University of Science and Technology, Sylhet 3114, Bangladesh c Environmental and Atmospheric Chemistry Laboratory, Atomic Energy Center, Bangladesh Atomic Energy Commission, Dhaka 1000, Bangladesh ARTICLEINFO Keywords: Trace metal Pollution Seasonal Ecosystem Bay of Bengal ABSTRACT We aimed to determine the temporal variation of trace metals concentrations in surface water and surface sediment samples at Kutubdia Channel, Bangladesh. Trace metals of samples were detected using energy dis- persive X-ray fuorescence (Energy-dispersive X-ray spectroscopy) method. The lowest concentration of metals was found in water samples during post-monsoon season and the highest during pre-monsoon season (Cu: 0.030 ± 0.001 μg/L in pre-monsoon and 0.026 ± 0.002 μg/L in post-monsoon, Zn: 0.087 ± 0.003 μg/L in pre-monsoon and 0.073 ± 0.002 μg/L in post-monsoon, Fe: 0.080 ± 0.001 μg/L in pre-monsoon and 0.055 ± 0.001 μg/L in post-monsoon). In contrast, metal concentration in surface sediment samples were higher in post-monsoon than in pre-monsoon season i.e. Cr 11 mg/kg in pre-monsoon and 12 mg/kg in post- monsoon, Mn 571 mg/kg in pre-monsoon and 606 mg/kg in post-monsoon, As (8 mg/kg in pre-monsoon and 10 mg/kg in post-monsoon, Pb (22 mg/kg in pre-monsoon and 24 mg/kg in post-monsoon, and Fe 2317 mg/kg inpre-monsoonand2435mg/kginpost-monsoon.Wefoundaspatialgradientofhightomediumtolowintrace metal concentration from river to river mouth to ofshore area. Considering the sources of metals, land erosion by waves and tidal action, an infux of water and sediment from the surrounding rivers, agricultural waste, industrial efuent and sewage are the most likely sources of metal pollution in the study area. We conclude that proper management strategies should be adopted to control the pollution and conserve the ecosystem health. 1. Introduction Heavy metals are considered as one of the major anthropogenic con- taminants in coastal and marine environments worldwide (Yu et al., 2008). Due to having toxicity, persistence and bioaccumulation char- acteristics, heavy metals pose a serious threat to human health, living organisms and natural ecosystems (DeForest et al., 2007). For example, heavy metals can lead to degradation of marine ecosystems by reducing species diversity and abundance, and through accumulation of metals in living organisms and food chains (Hosono et al., 2011). For example, when heavy metal contaminations occur in the aquatic ecosystem, it transfers to the higher trophic levels and ultimately reduces fsheries production. It is now evident that with the rapid industrialization and economic development in coastal regions, heavy metals are continuing to be introduced to estuarine and coastal environment. This generally occurs through rivers, runof, and land-based point sources where metals are produced as a result of metal refning by-products (Yu et al., 2008). When heavy metals fnd their way in the marine environment, most of metals generally deposit into sediments together with organic matters, Fe/Mn oxides, sulfdes, and clay (Wang and Chen, 2000). Depending on hydro- dynamic factors, biogeochemical processes and environmental conditions of rivers or maritime channels, sediments are recognized as an important sink of heavy metals in aquatic ecosystems (Pekey, 2006). These hydro- dynamicfactorsincludetidalinfuence,natureofwaveenergyandcurrent fow. However, it is important to note that, sediment generally cannot fx metals permanently. Some of the sediment bound metals might be re- leased into the water body again through various processes of re- mobilization under fuctuating conditions. Therefore, sediments are the main repository and secondary source of heavy metals in the marine en- vironment. In addition, sediments play an important role in transporting and storing of potentially hazardous metals (Krishnakumar et al., 2017). Estuarine environments are the meeting place of freshwater from rivers and salt water from the sea. Thus, they are considered as dynamic environments characterized by large fuctuations in environmental https://doi.org/10.1016/j.ecoenv.2020.110347 Received 11 October 2019; Received in revised form 14 February 2020; Accepted 15 February 2020 ∗ Corresponding author: Department of Oceanography, Shahjalal University of Science and Technology, Sylhet, 3114, Bangladesh. Mobile: +8801920314841 E-mail addresses: solaiman-ocg@sust.edu (Md. S. Hossain), kawser_du@yahoo.com (Md. K. Ahmed), subratasrk-ocg@sust.edu (S. Sarker), safur_baec@yahoo.com (M.S. Rahman). Ecotoxicology and Environmental Safety 193 (2020) 110347 0147-6513/ © 2020 Elsevier Inc. All rights reserved. T