Heavy metals contamination of cobalt (Co), nickel (Ni), arsenic (As), cadmium (Cd), and lead (Pb) and their ecological risks in seagrass sediments of the Pulai River Estuary, Malaysia.

Heavy metal contamination in coastal sediments presents ecological risks, particularly in rapidly developing regions like Southeast Asia. This study assesses the distribution, speciation, and environmental risk of cobalt (Co), nickel (Ni), arsenic (As), cadmium (Cd), and lead (Pb) in surface seagrass sediments from the Pulai River Estuary, Malaysia. Total and sequential extraction methods were employed to evaluate metal bioavailability. Results indicated that Ni (18.47 ± 1.37 µg/g) and Pb (17.79 ± 0.44 µg/g) were the most abundant elements in the total concentrations, whereas As (19.04 ± 0.70 µg/g) exhibited the highest concentration in the sequential extraction fractions. Sequential extraction results indicated mixed natural and anthropogenic sources, mainly from industrial discharges contributing to elevated As concentrations, while other metals remained in stable forms. Although geochemical indices of Enrichment Factor (EF), Geoaccumulation Index (Igeo), Contamination Factor (CF), and Pollution Load Index (PLI) generally classified the sediments as non-polluted, a comparison with the Sediment Quality Guidelines of Effect Range-Low (ERL) revealed potential biological risks associated with elevated Ni and As concentrations. These findings highlight the necessity for long-term monitoring and mitigation strategies to protect seagrass ecosystems in the Pulai Estuary.