Heavy metal contamination in sediments of the Sematan-Serayan River, Sarawak: Assessment of pollution indices and environmental risk implications

Sediments in river systems act as both sinks and sources of pollutants, which can have significant environmental and health implications. This study aimed to assess the concentrations of heavy metals in relation to total organic carbon (TOC) in the sediments of the Sematan-Serayan River, Sarawak, Malaysia. Sediment samples were collected in November 2024. Heavy metal and TOC concentrations were analysed via flame atomic absorption spectroscopy and a TOC analyser, respectively. The average heavy metal concentrations decreased in the order of Fe > Al > As > Zn > Ni > Cr > Pb > Mn > Cu > Co > Cd. Higher heavy metal concentrations associated with TOC were observed, particularly at stations close to anthropogenic activities, indicating pollution hotspots. The surface sediments were dominated by sand (> 90%). Pollution indices, including the contamination factor (CF), geoaccumulation index (Igeo), pollution load index (PLI), and potential ecological risk index (RI), were used to assess the severity of environmental pollution. All the stations were highly contaminated (CF > 6) and moderately to strongly polluted by Pb and As (Igeo > 2). Moreover, Stations 1 and 3-7 were considered deteriorated zones during the monsoon season (PLI > 1). The RI was very high (RI > 600) for Pb, As, Cu, Zn, and Cr at all stations. A comparison of the pollution indices with hierarchical cluster analysis suggested that anthropogenic activities were the main sources of heavy metal contamination in this river, potentially disturbing the biological functions of the benthos.