A study was conducted to investigate heavy metal content in sediments collected from the whole area of Tongi canal, close to Dhaka city of Bangladesh. Total concentration of metals in aquous extract of sediments was determined by Atomic Absorption Spectrophotometer (AAS) and the range of Cu, Zn, Pb and Fe varied from 18.34 to 101.27, 92.80 to 1111.15, 18.42 to 38.11 and 12327.5 to 47112.5 μg g^-1, respectively while there was trace amounts of Cd. The study results showed that the mean concentrations of Cu, Zn and Pb in sediments of Tongi canal were higher compared to geochemical standard and other Bangladeshi rivers. The average concentrations of Cu, Zn and Pb in the carbonate fraction were 7.07, 40.13 and 2.06 μg g^-1, respectively which can be released to the sediment pore water in acidic conditions. The calculated geoaccumulation index (I_geo) for Zn in 85% sampling sites exhibited I_geo class 1-3, indicating moderately to strongly polluted sediment quality. But in most cases, I_geo values for Cu and Pb exhibited I_geo class 1, indicating moderately polluted sediment quality. Similarly, the calculated enrichment factors (EFc) for 100 and 88% sampling sites had values >5.0 for Zn and Pb, respectively indicating anthropogenic pollution load for these metals. As regards to risk assessment code (RAC), Zn and Cu come under the medium risk category, while Pb comes under low risk category. The study concluded that the degree of contamination due to Zn, Pb and Cu in the study area was comparatively high, so it is desirable to take necessary initiative to minimize the pollution level as well as to monitor their concentrations in water and sediments routinely in future.

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Heavy Metal Contents in Sediments of an Urban Industrialized Area—A Case Study of Tongi Canal,Bangladesh