Heavy Metal Contamination and Ecological Risk Assessment in the Bhairab–Rupsha River Basin: An Integrated Approach Using Pollution Indices, Spatial Mapping, and Multivariate Analysis

ABSTRACT Heavy metal contamination in tidal river systems is an increasing environmental concern in rapidly urbanizing regions of South Asia. This study presents an integrated assessment of heavy metal pollution and ecological risk in the Bhairab–Rupsha River basin, Bangladesh. Concentrations of six priority metals—chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb)—were determined in water and surface sediments collected during the pre‐ and post‐monsoon seasons using inductively coupled plasma–mass spectrometry (ICP–MS). Data quality was ensured through strict QA/QC procedures. Pollution and ecological risks were evaluated using the heavy metal pollution index (HPI), heavy metal evaluation index (HEI), water–sediment concentration factor ( K d ), contamination factor ( C f ), degree of contamination ( C d ), pollution load index (PLI), geo‐accumulation index ( I geo ), ecological risk factor ( E r ), potential ecological risk index (PER), spatial mapping, and principal component analysis (PCA). Water samples showed the concentration order as follows: Cu > Cr > Ni > Pb > Zn > Cd, with Cr, Cd, and Pb exceeding the Bangladesh Environmental Conservation Rules and the relevant United States Environmental Protection Agency (USEPA) and CCME aquatic life guidelines. HPI values exceeded the critical limit (>100) at all stations, indicating severe water quality deterioration, particularly downstream. In contrast, sediment metal concentrations remained below guideline thresholds, with C f < 1, C d < 8, PLI < 1, I geo < 0, and PER indicating low ecological risk. Spatial analysis revealed increasing downstream enrichment associated with industrial discharges, municipal wastewater, and port activities. PCA explained 98.8% of the total variance, suggesting a dominant anthropogenic source of contamination.