Microplastic and copper contamination in coastal waters: Accumulation in zooplankton and caged milkfish (Chanos chanos), and metallothionein response in fish

This study investigates anthropogenic pollution in the coastal waters of Tanjung Mas, Semarang, focusing on microplastic and copper concentrations in zooplankton and caged milkfish (Chanos chanos) reared in fixed net cages, as well as metallothionein responses in the fish. Zooplankton, milkfish, and seawater were collected from four stations (T1, T2, T3, and T4) with varying degrees of anthropogenic activity at different times and fish ages, and were analyzed for microplastic abundance, copper concentrations, and metallothionein levels. Microplastics were detected in all environmental and biological matrices, with the highest concentrations found in surface water at Station T1, in zooplankton, and the digestive tracts of milkfish. Black-colored fibers and fragments were the dominant types, suggesting sources such as textile waste, fishing gear, and plastic packaging. Fourier Transform Infrared spectroscopy identified the presence of PETE, PC, EVA, and PVC polymers. Copper concentrations exceeded national water quality standards, with the highest bioaccumulation observed in the gills and digestive tracts of fish, indicating potential toxicological risks. Metallothionein levels varied across fish tissues, with the highest levels found in the digestive tract, and correlated positively with Cu concentrations, indicating a metal-induced stress response. No significant relationship was found between fish age and the accumulation of microplastics or metallothionein, suggesting that environmental exposure was the primary factor. These findings highlight the potential of C. chanos as a bioindicator species for monitoring coastal pollution, providing a scientific basis for the development of targeted management and mitigation strategies.