Comprehensive index analysis approach for ecological and human health risk assessment of a tributary river in Bangladesh

This study examined the water quality of the Turag River, an important tributary river in Dhaka, Bangladesh in terms of physicochemical characteristics and heavy metal contamination to assess the potential risks to both ecological systems and human health. The majority of the water samples complied with the acceptable limits established by the World Health Organization (WHO) for various parameters including pH, electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), chemical oxygen demand (COD), sodium adsorption ratio (SAR), and magnesium adsorption ratio (MAR), except total hardness (TH). The sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), chloride (Cl-)(,) fluoride (F-), nitrate (NO3-), and sulfate (SO42-) levels in the water samples were found to be within acceptable ranges for most cases. Moreover, heavy metals including lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), arsenic (As), selenium (Se), and mercury (Hg) were analyzed and their mean concentrations (mu g/L) were found in the order of Fe (244.72 +/- 214.35) > Mn (28.93 +/- 29.64) > Zn (22.97 +/- 10.93) > Cu (8.28 +/- 5.99) > Hg (8.23 +/- 6.58) > As (1.34 +/- 0.39) > Ni (1.20 +/- 0.38) > Cr (0.67 +/- 0.85) > Pb (0.61 +/- 0.72) > Se (0.42 +/- 0.48) > Cd (0.13 +/- 0.09) which were within the acceptable limit, except Hg. The cumulative effect of all heavy metals was assessed through the heavy metal pollution index (HPI), contamination degree (C-d), and nemerow pollution index (P-N). The mean value of HPI (682.38 +/- 525.68) crossed the critical index value of 100, indicating an elevated level of pollution. The mean value of C-d (8.763 +/- 6.48) indicates a low-moderate-significant level of contamination due to an elevated level of Hg, and for the P-N it was found 174.27 +/- 146.66, indicating a high level of pollution due to high level of Fe. Ecological risk index (ERI) indicated low levels of risk for Pb, Cd, Cr, Ni, Fe, Mn, As, Se, Cu, and Zn but a significantly high risk for Hg. The water was classified as good to excellent based on its physicochemical properties (pH, EC, TDS, COD, DO, F-, Cl-, NO3-, and SO42-) while it was deemed poor to unsuitable for heavy metals according to the water quality index (WQI). Among the carcinogenic constituents, As poses the greatest carcinogenic risk, particularly for children. The mean value of Cr, Mn, and As in the HQ(ingestion) for adult and child, and Cd, Hg for child exceeded the threshold value established by the United States Environmental Protection Agency (USEPA), while the HQ(dermal) values remained below the maximum limit for all heavy metals. The value of HI at all locations exceeds the threshold of 1, as specified by USEPA. Principal component analysis (PCA) and cluster analysis revealed that the presence of heavy metals in the Turag River was mainly attributed to anthropogenic sources, including industrial effluent discharge from neighboring industries, domestic wastewater, and agricultural runoff containing agrochemicals from the surrounding lands.