Developing nations, such as Bangladesh, face an enormous crisis in maintaining natural sustainability due to heavy metal contamination by the peripheral rivers. Frequent heavy metals discharged from tanneries, dyeing, and potential anthropogenic activities in Savar city pollute the Dhaleshwari river, which is an important river of the capital city, Dhaka. The present study aimed to assess the heavy metals contamination in the Dhaleshwari river sediment and evaluate the subsequent ecological risk indices emerging from the deposits. The contamination levels of heavy metals such as lead (Pb), cadmium (Cd), chromium (Cr), and nickel (Ni) were analyzed in the Dhaleshwari River sediment. Various environmental indices, such as Potential Enrichment Risk (PER), Geo-accumulation Index (Igeo), Enrichment factor (EF), Toxic unit analysis (TUs), etc., were observed in various compartments. The concentration of heavy metals ranged as follows: Lead (Pb), 297.3-414.6 mg/L; Cadmium (Cd), 1.5-4.4 mg/L; chromium (Cr), 97.9 -282.4 mg/L; Nickle (Ni), 85.1-264.5 mg/L; Iron (Fe), 11800-14375 mg/L. The metal concentrations were higher than the threshold effect level (TEL) and probable effect level (PEL) standards. Based on the TUs, the probability of toxicity is about 76% (TU > 2.3) at the Dhaleshwari river. Comparative evaluation of different environmental indices between present and past studies indicated progressive deterioration of sediments by heavy metals. Linear correlations of heavy metals in sediment samples demonstrated toxic accumulation of heavy metals in the surrounding ecosystem. The study outcomes emphasize the necessity of systematic investigation in the Dhaleshwari river and warranting effective prioritization to ensure river health over industrial wastewater discharge.

Natural radioactivity levels in the eastern coastline of Lake Hawassa sediment samples of Ethiopia’s Sidama Region have been measured. Sediment samples were collected and analyzed using gamma-ray spectrometery (high purity germanium detector) to evaluate the radioisotopes of 238U (214Pb, 214Bi), 232Th (228Ac, 212Pb), and 40K and their ranges of activity concentrations were 11.70 to 29.73 Bq 〖kg〗^(-1), 19.01 to 58.61 Bq 〖kg〗^(-1), and BDL to 827.21 Bq 〖kg〗^(-1) ,with average values of 16.51 ± 1.20 Bq 〖kg〗^(-1) , 28.17 ± 2.27 Bq 〖kg〗^(-1) ,and 673.95 ± 29.92 Bq 〖kg〗^(-1) (dry mass), respectively. The radiological hazard indices average values (radium equivalent (R_eq) (108.69 Bq 〖kg〗^(-1) ); hazard index (H_ex (0.29); excess lifetime cancer risk (ELCR) (0.23 x 〖10〗^(-3) ); absorbed dose rate (D_R) (52.70 nGyh^(-1) ); annual effective dose equivalent (AEDE) (0.07 mSv〖yr〗^(-1)); and annual gonadal dose equivalent (AGDE) (0.38 mSv〖yr〗^(-1)) were also evaluated and compared to the worldwide-recommended values. All results of radiological hazard indices obtained in this study were lower than their worldwide-recommended values were 370 Bq 〖kg〗^(-1), ≤1, 59 nGyh^(-1), 0.07mSv〖yr〗^(-1), 0.29 × 〖10〗^(-3), and 0.3mSv〖yr〗^(-1) of radium equivalent activity, external hazard index, outdoor absorbed dose rate, outdoor annual effective dose equivalent, excess lifetime cancer risk, and annual gonadal dose equivalent, respectively. This suggests the eastern coastline of Lake Hawassa is safe from radioactive risk for aquatic species and various human activities, and appears as essential radiometric baseline information for further environmental monitoring programs.