Physiological impacts of microplastics, heavy metals, and metallothionein in milkfish <em>(Chanos chanos)</em> in Jakarta Bay, Indonesia

Several anthropogenic activities are renowned for causing microplastic (MP) pollution and heavy metal accumulation. Therefore, this study aimed to analyze the concentrations of MPs, metallothionein (MT) and heavy metals found in milkfish (Chanos chanos) in Jakarta Bay. The samples were taken from five locations, namely, Marunda in North Jakarta, Muara Gembong in Bekasi, Teluk Naga and Pandeglang in Banten and East Lampung in Lampung. Separation and destruction of the gills and the digestive tract of milkfish were carried out via nitric acid (HNO3). The samples were subsequently analyzed to assess the abundance of MPs via light microscopy, and the MT concentration was measured via the MT ELISA Kit (enzyme-linked immunosorbent assay kit). MT analysis was then complemented by an evaluation based on literature studies and assessment of protein interactions via STRING (string-db.org). Heavy metal analysis in milkfish was performed via the inductively coupled plasma (ICP) method. The results revealed that the average number of MP fibers across the five locations was 11.67. In terms of MT, Marunda had the highest protein expression in the gills and digestive tract, with values of 72.56 pg/mg and 245.44 pg/mg, respectively. The observation of lead (Pb) heavy metals suggested that the highest level was found in East Lampung (0.11 mm/kg), whereas Marunda (0.07 mm/kg) had the lowest level. The MT protein is involved in the mechanism of cell stress pathways, indicating the occurrence of severe pollution in Jakarta Bay. Thus, this study provides evidence of pollution in Jakarta Bay by evaluating the MP and heavy metal statuses and offering information regarding the physiological impacts on aquatic organisms. This valuable information is essential for future regulations.