Seasonal variations of trace metals from water and sediment samples in the northern Bay of Bengal.

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 dispersive X-ray fluorescence (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 in pre-monsoon and 2435 mg/kg in post-monsoon. We found a spatial gradient of high to medium to low in trace metal concentration from river to river mouth to offshore area. Considering the sources of metals, land erosion by waves and tidal action, an influx of water and sediment from the surrounding rivers, agricultural waste, industrial effluent 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.