Characterization of heavy metal in the peripheral rivers around Dhaka City

Abstract

Dhaka city is surrounded by a number of rivers and canals of which Tongi Canal, Turag, Buriganga, Dholeshwari, Balu and Shitalakhya are most important. These rivers receive partially treated and untreated sewage effluent, sewage polluted surface runoff and untreated industrial effluent through different government authority from nearby residence and industrial areas. The rivers are further polluted by indiscriminate throwing of household, clinical, pathological and commercial wastes and discharge of spend fuel and human excreta. In fact, the rivers have become dumping ground of all kinds of solid, liquid and chemical waste of bank-side population. This study provides an assessment of the present status of water quality based on analysis of water sample collected from fourteen stations and sludge samples collected from four stations of the peripheral river around Dhaka City (Fig-1.1). Nine parameters (As, Cd, Cr, Ni, Pb, Zn, pH, TSS, and TDS) were analyzed for each water samples. Six parameters (As, Cd, Cr, Ni, Pb and Zn) were analyzed for each sludge samples. Highest 3.28 ppb As found in peripheral rivers was less than 200 ppb (Discharge in Inland Water). Highest 0.018 mg/l Cd found in surface water at PSTP outlet was less than 0.05 mg/l (Discharge on Irrigated Land). Highest 4.115 mg/l Cr found in surface water at Chandnighat was exceeds 0.50 mg/l (Discharge in Inland Water) and 1.0 mg/l (Discharge into Public Sewer and Discharge on Irrigated Land). Highest 0.089 mg/l Ni found in surface water at PSTP outlet was less than 1.0 mg/l (Discharge in Inland Water). Highest 0.224 mg/l Pb found in surface water at PSTP outlet was greater than 0.10 mg/l (Discharge in Inland Water and Discharge on Irrigated Land). Highest 2.055 mg/l Zn found in Confluence of Balu River & Norai Khal was less than 5.00 mg/l (Discharge in Inland Water). US EPA sediment quality guideline, metal concentration ranged between As: 0.037-0.096, Cd: 1.50-2.90, Cr: 38.70-56.20, Ni: 19.30-28.90, Pb: 69.90-88.10 and Zn: 87.10-95.90 mg/kg in the Saidabad and Chandighat WTP intakes sediments. Pb belongs to heavily polluted, Cr belongs to moderately polluted, Ni and Zn belongs to not polluted to moderately polluted and As and Cd belongs to not polluted for the Saidabad and Chandighat WTP intakes sediments.