Seasonal variations of trace metals from water and sediment samples in the northern 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 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±0.001μg/L in pre-monsoon and 0.026±0.002μg/L in post-monsoon, Zn: 0.087±0.003μg/L in pre-monsoon and 0.073±0.002μg/L in post-monsoon, Fe: 0.080±0.001μg/L in pre-monsoon and 0.055±0.001μg/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 11mg/kg in pre-monsoon and 12mg/kg in post-monsoon, Mn 571mg/kg in pre-monsoon and 606mg/kg in post-monsoon, As (8mg/kg in pre-monsoon and 10mg/kg in post-monsoon, Pb (22mg/kg in pre-monsoon and 24mg/kg in post-monsoon, and Fe 2317mg/kg in pre-monsoon and 2435mg/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.