Evaluation of heavy metal pollution and ecological risk of surface sediments in a tropical mountainous River-Estuary-Shelf Continuum system: A case study of the Selangor River, Malaysia

As human activities continue to increase, the global production of pollutants has increased significantly, with the majority of pollutants being transported to the ocean via rivers, resulting in intensified pollution in estuaries and coastal areas. To maintain a healthy marine ecological environment, it is necessary to consider rivers, estuaries, and coastal seas as integrated systems and implement pollution management based on the concept of land-ocean integration. In this study, heavy metal elements in the surface sediments of Selangor River-Estuary-Coastal Shelf Continuum were collected and analysed to assess their pollution levels and potential ecological risks. The results show that the heavy metal content is high in the downstream and estuarine regions, with a general decreasing trend observed from nearshore to offshore in the coastal shelf area. The heavy metal pollution assessment indicates that the surface sediments of the Selangor River-Estuary-Coastal Shelf continuum were contaminated, with the most severe pollution occurring downstream and within the estuary. The pollution levels gradually decrease after exiting the estuary. The ecological risk associated with heavy metal pollution in rivers, estuaries, and southeastern coastal areas was classified as moderate to serious, whereas other areas exhibited only slight ecological risks. Specifically, As causes serious pollution in the river and estuary, with moderate-to-serious pollution in the coastal shelf area and moderate-to-serious ecological risks, mainly originating from mining within the river basin. Pb causes moderate pollution in the river, estuary, and coastal areas, with slight ecological risks due to mining within the river basin and inputs from nearby rivers, ports, and industrial activities. Other heavy metals cause minor pollution and pose minimal ecological risks.