Turag river, passing through the northwestern part of Dhaka city, plays a significant role as the main drainage channel and carries water to the Buriganga river. The major pollution sources of Turag River are untreated effluents from different industrial establishments, domestic and human waste from surrounding municipalities and slum areas. This study identified and categorized the major sources of pollution and outfalls discharging into Turag river. Evaluation of spatial and temporal variation of surface water parameters was performed throughout a year including assessment of risks on the overall ecosystem. Finally, status of heavy metal contamination of different compartments of Turag river such as river water, riverside plants, sediment, phytoplankton and fish species belonging to different trophic levels was evaluated. Results indicated that currently, Turag river is being polluted by 15 point sources including industrial effluent and municipal sewage. Specific point sources such as Azmeri knit composite, Hossain Dyeing, Tongi Bridge waste, Mehmud Industries Limited and Fish market waste were identified within the stretch of the study. Major outfalls included storm sewer pipes, open channels and small/big private outfalls. Dissolved oxygen was obtained below 4 mg/L in most instances and accordingly, it was difficult to find common aquatic life forms especially during dry season. Levels of biochemical and chemical oxygen demand, color, turbidity, total suspended solids, faecal and total coliforms, ammonia, nitrate and phosphate were obtained beyond the standard water quality ranges. Certain fish species and macroinvertebrates were categorized to be endangered comparing current and previous observation. Chromium, cadmium, lead and copper were detected at negligible levels in the water however, significant concentrations of zinc were obtained in plants, phytoplanktons and riverside sediments. Pollution Load Index indicated low level of heavy metal contamination and bioconcentration factors suggested significant bioaccumulation of zinc in phytoplanktons and moderate level of accumulation in fish species.
Nehreen Majed– Associate Professor, University of Asia Pacific, Dhaka, Bangladesh