Geogenic mercury in Indonesia: A critical review of occurrence patterns, geological controls, and environmental...

Indonesia is one of the world's most tectonically and volcanically active regions, providing a unique natural setting for the geogenic release and redistribution of mercury (Hg) in the environment. Despite the increasing number of Hg-related studies, a comprehensive synthesis that integrates the occurrence patterns, geological controls, and environmental pathways of geogenic Hg is lacking. This study critically synthesises geogenic Hg research in Indonesia by classifying the existing literature into major geological and environmental clusters and proposing national research priorities. A combined bibliometric analysis and PRISMA-guided systematic review were conducted on peer-reviewed literature indexed in Scopus from 2005 to 2025. After rigorous screening, geogenic Hg studies were synthesised to identify four principal occurrence clusters: volcanic and geothermal systems, lithogenic systems, mud volcano systems, and natural aquatic systems. The results demonstrate that geogenic Hg in Indonesia is governed by geological context and reservoir conditions, which regulate Hg retention, mobilisation, and transfer rather than emission magnitude alone. Across these systems, geogenic Hg undergoes deposition, mobilisation, methylation, and bioaccumulation, strongly enhanced under tropical hydroclimatic conditions and high biological productivity. In addition, this study integrates disparate evidence into a source-process-pathway framework describing geogenic Hg dynamics across geological and environmental systems in Indonesia. Based on these findings, four national research phases are proposed: baseline mapping, process-based studies, multi-media risk modelling, and policy-oriented monitoring and management. This synthesis advances the process-based understanding of geogenic Hg dynamics in Indonesia and offers transferable conceptual insights to address unresolved questions in global geogenic Hg research.