Sanchita Dewanjee

Trace metal contamination in sediments is a global concern. This study aimed to assess the contamination level of trace metals, their sources, and ecological risk in surface sediments of Karnaphuli River—a tropical urban river in Bangladesh. Forty-five sediment samples were analyzed by atomic absorption spectrophotometry (AAS) for Cu, Fe, Zn, Pb, Cr, Cd, and Ni metals along with physicochemical parameters like pH and organic matter (OM). The pollution status and potential ecological risk were assessed by using the geo-accumulation index (I_geo), contamination factor (CF), and potential ecological risk index (PERI). Source identification of trace metals was performed by correlation analysis, cluster analysis, and principal component analysis (PCA). The results show that the range of Cu, Fe, Zn, Pb, Cr, Cd, and Ni concentrations were 0.62–1.61 mg/kg, 23.95–85.70%, 0.52–1.89 mg/kg, 7.99–12.90 mg/kg, 33.91–65.47 mg/kg, 0.77–1.17 mg/kg, and 2.73–5.36 mg/kg, respectively. The concentrations of Fe, Cd, and Cr were above the permissible limits while the contamination factor (CF) and geo-accumulation index (I_geo) values revealed that Fe and Cd were the most dominant pollutants. Cluster analysis and PERI exhibited significant anthropogenic intrusions of trace metals. A significant positive correlation between Fe-Cr, Cr-Ni, Fe-Ni, and Pb-Cd shows their common anthropogenic source and influences. PERI also revealed that Cr, Fe, and Cd have a significant contribution with a moderate to considerable potential threat.

The potential of biodegradable polymers has long been appreciated. In this work, an attempt has been made to synthesize biodegradable polymer composite from potato starch and low density polyethylene (LDPE) with different ratios of starch (0%-15% w/w) by using an extruder. The structure and morphology of film surfaces was studied using X-ray diffraction and scanning electron microscopy (SEM) respectively. The physical (density, water absorption), mechanical (tensile, flexural) and thermal (TGA and DTA) analyses of starch/LDPE bio-composites were evaluated through standard methods and instruments. Biodegradation tendency was investigated utilizing soil burial and Rockwell micro-hardness test.The results revealed that the density and water absorption of polymer blends increased with increasing the starch content in starch/LDPE composites. The tensile strength and elongation at break decreased with starch content whereas the elastic modulus, flexural strength and flexural modulus rose. The biodegradability of composites enhanced by increasing the starch content and the result was backed by weight loss during burial of the samples in soil for 90 days. Microhardness test also supported the biodegradation probability as hardness found to reduce extensively after soil burial. However, further study to decide the optimum starch loading alongwith some modifications to starch and LDPE is highly suggested to have a biodegradable LDPE polymer composite in a realistic time frame.