How dynamic is the heavy metals pollution in the Buriganga River of Bangladesh? A spatiotemporal assessment based on environmental indices

Frequent discharge of heavy metals from textiles, tanneries and other anthropogenic sources occurs in Dhaka City, the capital of Bangladesh, contaminating the major rivers. Accumulation of heavy metals such as chromium (Cr), cadmium (Cd), lead (Pb), nickel (Ni) and zinc (Zn) in water, sediment, phytoplankton and fish species was investigated in Buriganga River, a major river of Dhaka City. Three different discharge points (Basila Bridge, Hazaribagh and Babu Bazar) were selected based on their proximity to heavy industrial discharges. Plant Enhydra fluctuans, phytoplankton Lemnoideae and fish species such as Heteropneustes fossilis, Channa striata, Corica soborna and Wallago attu of the Buriganga River were analyzed for heavy metals. Different environmental indices were determined (e.g., contamination factors, plant concentration factors, biomagnification factors, etc.), and correlations among concentrations in different compartments were obtained. Concentrations of Cr, Cd and Pb were above the toxicity reference values (TRV) for surface water quality standards applicable for aquatic life. Chromium (Cr) was found at very high levels 103 mg/kg in soil and 163 mg/kg in the plants in Hazaribagh tannery wastes discharge point. The biological samples had enough evidence for bioaccumulation of metals. Although environmental indices exhibited signs of improvement, evidence of higher level of metals in sediment, plants and fishes seemed alarming. Positive correlations among heavy metal concentrations in soil, water and plants indicate linear dependence of heavy metals accumulation from water and soil into the plants. This study emphasizes the necessity of controlling the point and nonpoint urban pollution sources discharging into the Buriganga River.