Magnetic susceptibilites of suspended sediment and microplastic abundance in a tropical volcanic estuary

Coastal and estuarine ecosystems are seriously threatened by pollutants, according to the literature. In the estuary, the zone that traps suspended particulate matter, namely, estuarine turbidity maxima (ETM), needs to be identified to prevent ecological threats, namely migration and species death. Magnetic measurements of sediments in volcanic rivers have also attracted attention because the sediment contains a high abundance of magnetic minerals. The method in this paper provides a low-cost, rapid, and nondestructive approach to environmental monitorings and assessments. However, the validity of magnetic measurements has not been investigated for their use in identifying the ETM zone in estuaries in volcanic regions. Therefore, this research aims to identify ETM zones in the estuaries of volcanic regions using magnetic properties to correlate the characteristics to microplastic abundance within suspended and surface sediments. The measurements consist of magnetic susceptibility at low frequency, magnetic susceptibility at high frequency, frequency-dependent magnetic susceptibility analyses, and acquisition of a hysteresis curve. Magnetic minerals were also identified using X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy. The results showed that the values of magnetic susceptibility at low frequency significantly correlate with total dissolved solids and microplastics abundance in sediments. The frequency-dependent magnetic susceptibility values were significantly correlated with total dissolved solids, microplastics abundance, turbidity, and microorganism cells. This phenomenon indicates that the magnetic properties of suspended sediments can be used to identify an ETM zone in estuaries in tropical volcanic regions.