ASSESSMENT OF HEAVY METALS IN SEDIMENT, WATER, AND FISH OF THE TURAG RIVER, DHAKA CITY, BANGLADESH

Abstract

Metal pollutant has a harmful effect on biological systems and does not undergo biodegradation, therefore gets accumulated in the river bed, water, and into aquatic life. The present study intends to assess the level of contamination of sediments, water, and fish by heavy metals in the Turag River flowing through the Northern and Western sides of Dhaka City. To estimate the geochemical environment of the river, five trace elements, namely Cr, Cu, Cd, Pb, and Fe, were extracted from the freshly deposited river bed sediments, water, and fish of Turag River using a Di-acid mixer and analyzed at the Central Laboratory of the SAU using Atomic Absorption Spectrophotometer (Analytik Jena NovAA 400P). All the sediment and water samples were collected from eleven different locations and after preparation, samples were analyzed using standard procedure. Trace element contamination assessment reveals that the benthic sediment and water are contaminated at low to moderate levels in these areas, with a common trend of concentration of Fe>Cr>Cu>Pb>Cd for sediment, Fe>Cu>Cr>Pb>Cd for water, and fish. This indicates that the untreated and/or partially treated industrial and municipal wastewater discharges along the river bank might be the major sources of pollution. Results showed that metal concentration in sediment ranged between 0.11 to 3.81 mg/kg for Cd, 0.63 to 6.74 mg/kg for Pb, 43 to 201 mg/kg for Cr, 6.84 to 62.87 mg/kg for Cu, 1278 to 1831 mg/kg for Fe in the rainy season and 0.14-3.72 mg/kg for Cd, 0.34-12.85 mg/kg for Pb, 48-239 mg/kg for Cr, 22.7-49.62 mg/kg for Cu, and 1777-1885 mg/kg for Fe in the winter season. In water samples, the results also showed that metal concentrations ranged from 0.16-0.5 mg/kg for Cd, below the detection limit for Pb and Cu, 0.21-0.3 mg/kg for Cr, and 0.44-2.31 mg/kg for Fe respectively in the winter season and the metal concentrations also ranged from 0.4-3.61 for Fe, below the detection limit for Pb, Cr, Cu, and 0.04 mg/kg for Cd in one station among eleven in rai ny season which is ignorable. In the case of fish, five species have only been found during the rainy season. There is no fish was found in the winter season due to higher pollution. The average results from these species are 0.55 mg/kg for Cd, 0.28 mg/kg for Pb, 0.65 mg/kg for Cr, 3.14 mg/kg, and 894.56 mg/kg for Fe. The highest contamination degree of the sediment was noticed at Location 1 (Amin Bazar Bridge, Gabtoli) and the lowest at Location 6 (near Dhaka Ashulia Highway), and the highest degree of water contamination was noticed at location 1, and the lowest contamination degree of water is noticed at location 6 in both rainy winter season. The contamination level varies systematically with the distance from the contamination source. However, it is anticipated that the sediment, water, and aquatic ecosystem may degrade in the near future due to increasing anthropogenic inputs in the river basin, hence proper management strategies are required to control the direct dumping of wastewater in the river.