Integrated Magnetic and Chemical Tracers for Monitoring Subsurface Contaminant Transport in Hydrothermally Altered and Wastewater Impacted Coastal Environments

Coastal environments impacted by hydrothermal alteration and anthropogenic wastewater intrusion face complex challenges in monitoring subsurface contaminant transport due to dynamic redox gradients, fluid mixing, and heterogeneous sediment properties. This review explores the integrated application of magnetic and chemical tracers as a powerful approach to understanding the sources, movement, and transformation of contaminants such as heavy metals, nutrients, and pharmaceuticals in these systems. Magnetic tracers including magnetite and greigite serve as indicators of redox conditions and sedimentary processes, while chemical tracers such as rare earth elements, stable and radiogenic isotopes, major ions, and contaminants of emerging concern provide high resolution information on contaminant sources and biogeochemical behavior. The review examines tracer detection methods, transport mechanisms, and reactivity, emphasizing the complementary nature of magnetic and chemical signatures in delineating contaminant plumes. Through illustrative case studies, the utility of this integrated framework is demonstrated in diverse coastal contexts, including estuaries, wastewater impacted aquifers, and hydrothermally influenced sediments. The findings highlight the value of combining particulate and dissolved phase tracers for environmental forensics, remediation monitoring, and long term water quality assessment. The review concludes by identifying key research opportunities in tracer based environmental monitoring, including the development of portable detection tools, machine learning integration, and the establishment of standardized tracer libraries. This synthesis reinforces the importance of interdisciplinary approaches for managing contaminant transport in vulnerable coastal ecosystems.