Advancing ecological risk assessment and developing site-specific water quality criteria for heavy metals in coastal waters

This study advances pollution assessment and management by deriving water quality criteria from ecotoxicological tests with native species, developing a Multi-Metric Heavy Metal Pollution Index (MMHPI) for sediment risk assessment, and applying criteria-based ecological risk assessment for water. Monitoring showed average dissolved cadmium of 1.05 ± 1.16 µg L-1 and sediment concentrations of 2.71 ± 3.22 mg kg-1, peaking in industrial zones. Hazard quotient values ranged from 0.44 (Aroor) to 2.41 (Pathalam), highlighting distinct areas of elevated dissolved Cd risk. Sediment Cd risk assessment based on multiple indices revealed substantial concern, with geoaccumulation index (1.08-3.15) indicating moderate to heavy pollution, contamination factor (3.18-13.32) reflecting considerable to very high contamination, and ecological risk factors (95.27-399.50) showing considerable to very high ecological risk. The MMHPI revealed distinct pollution hotspots, with very high risk at Cochin Barmouth (0.84), Chittoor (0.96), Eloor (0.90), and FACT (1.00), and high risk at Bolgatty (0.76) and Kadamakkudy (0.75). The protective criteria derived for cadmium were Criterion Maximum Concentration (CMC; 26.9 µg L-1), Criterion Continuous Concentration (CCC; 1.96 µg L-1), and Predicted No-Effect Concentration (PNEC; 0.98 µg L-1). Taken together, the findings confirm that cadmium contamination in both the water column and sediments constitutes a substantial ecological risk, necessitating coordinated monitoring and mitigation efforts. In this context, this science-based framework supports United Nations Sustainable Development Goals on clean water (SDG 6), responsible chemical management (SDG 12), and aquatic ecosystem protection (SDG 14), providing policymakers and stakeholders with effective strategies for monitoring and managing heavy metal pollution.