Accumulation of Heavy Metals in Long-Evans Rat Through Feeding Fishes of Buriganga River and Their Histopathological Evaluation

The study was conducted to evaluate the impacts of industrial discharges, including from tanneries, in terms of heavy metal loads in fin-fish of the Buriganga river, Dhaka, Bangladesh, and to find out the ultimate effects of feeding those heavy metal-contaminated fishes to Long-Evans rats to examine rats' heavy metal accumulation along with viable architectural alterations on various organs through histopathological screenings. Being the most edible by the populace, Labeo rohita was chosen for this purpose. Labeo rohita was collected from five different spots in the river close to the industrial outlets, covering three seasons: monsoon, winter, and summer throughout the year. Experiments unearthed that the deposition of heavy metals inside fishes always surpassed the standard margin, implying a pernicious aquatic milieu. The empirical data suggests that the mean concentrations of Cu, Pb, Cr, and Cd were higher than the permissible limits of WHO and FAO after feeding heavy metal-contaminated fishes for a period of 120 days. Seasonal variations were also taken into account, and it was noticed that rats fed with fish collected in winter had the highest heavy metal concentrations (P < 0.05). Significant architectural changes were observed during histopathological screening of rats' livers and kidneys characterized by necrosis, inflammation, and congestion. After gauging the obtained data, it might be concluded that consumption of heavy metal-contaminated fish entails accumulation of heavy metals, which causes histopathological changes in rats' livers and kidneys, including necrosis and severe structural deformational changes compared to those of control groups.

River toxicity assessment using molecular biosensors: Heavy metal contamination in the Turag-Balu-Buriganga river systems, Dhaka, Bangladesh

Pollution in rapidly urbanising cities and in delta systems is a serious problem that blights the lives and livelihoods of millions of people, damaging and restricting potable water supply and supplies to industry (Whitehead et al, 2015, 2018). Employing new technology based on luminescent molecular biosensors, the toxicity in the rivers around Dhaka in Bangladesh, namely the Turag, Tongi, Balu and Buriganga, has been assessed. Samples taken at 36 sites during medium and low flow conditions and during the Bishwa Ijtema Festival revealed high levels of cell toxicity, as well as high concentrations of metals, particularly aluminium, cadmium, chromium, iron, zinc, lithium, selenium and nickel. Chemical analysis also revealed low dissolved oxygen levels and anoxic conditions in the rivers at certain sites. The bacterial molecular biosensors were demonstrated to be fast, with results in 30 min, robust and a highly sensitive method for the assessment of water toxicity in the field. Furthermore, the biosensor toxicity analysis correlated with the metals data, and a multivariate regression relationship was developed relating toxicity to key metals, such a selenium, zinc and chromium. The resulting model has been validated against split samples and the Bishwa Ijtema Festival data. The combination of modelling and the molecular biosensor technology provides a new approach to detecting and managing pollution in urban river systems.

Monitoring of metal pollution in waterways across Bangladesh and ecological and public health implications of pollution

Using innovative artificial mussels technology for the first time, this study detected eight heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, U, Zn) on a regular basis in waterways across Bangladesh (Chittagong, Dhaka and Khulna). Three heavy metals, viz. Co, Cr and Hg were always below the instrumental detection levels in all the sites during the study period. Through this study, seven metal pollution "hot spots" have been identified, of which, five "hot spots" (Cu, Fe, Mn, Ni, Pb) were located in the Buriganga River, close to the capital Dhaka. Based on this study, the Buriganga River can be classified as the most polluted waterway in Bangladesh compared to waterways monitored in Khulna and Chittagong. Direct effluents discharged from tanneries, textiles are, most likely, reasons for elevated concentrations of heavy metals in the Buriganga River. In other areas (Khulna), agriculture and fish farming effluents may have caused higher Cu, U and Zn in the Bhairab and Rupsa Rivers, whereas untreated industrial discharge and ship breaking activities can be linked to elevated Cd in the coastal sites (Chittagong). Metal pollution may cause significant impacts on water quality (irrigation, drinking), aquatic biodiversity (lethal and sub-lethal effects), food contamination/food security (bioaccumulation of metals in crops and seafood), human health (diseases) and livelihoods of people associated with wetlands.