Ecological health risk assessment of heavy metals in sediments and freshwater fishes: tropical Cauvery river, South India

The Cauvery River is an essential water system in South India, vital for both ecological balance and the livelihoods of millions. However, urbanization, industrialization, and intensive agriculture have raised concerns over its water quality and ecosystem health, primarily due to the influx of heavy metals from anthropogenic sources. This study evaluates the spatial distribution and ecological risks of heavy metals in sediments and fish along the river. Sediment samples were collected from 18 sites (C1 to C18), and fish from 10 locations (S1 to S10), with analyses focusing on chromium (Cr), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). Pollution levels were assessed using several indices, including the geoaccumulation index (Igeo), contamination factor (Cf), degree of contamination (Cdeg), pollution load index (PLI), and potential ecological risk (PER). The mean concentrations of Zn (33.11 µg/g), Cu (28.98 µg/g), Pb (2.059 µg/g), and Cd (0.318 µg/g) remained within sediment quality guidelines. The Igeo values ranged from a maximum for Cd (0.30 to 1.98) to a minimum for Cu (-0.35 to 1.66), indicating moderate contamination by Cd and slight contamination by Pb (-2.91 to -5.09) and Zn (-0.83 to -3.06), particularly downstream. Fish heavy metal concentrations varied significantly between species, ranging from 0.154 ± 0.02 to 88.978 ± 4.71 µg/g. Principal component and cluster analysis revealed variations in trace metal accumulation in fish and spatial homogeneity. Heavy metal accumulation in fish tissues varied significantly across species, with several exceeding the threshold values for non-carcinogenic (THQ, HI > 1) and carcinogenic (risk > 10^− 4) health risks, especially for Cd and Pb. Although occasional fish consumption may not pose immediate health concerns, regular or excessive intake could lead to significant long-term health risks. Therefore, continued monitoring of heavy metal levels in both sediments and aquatic biota is essential to ensure food safety and protect public health.