History of heavy metal pollution recorded in sediments in the Taiwan Strait

Over the past five decades, Taiwan has experienced rapid economic development and industrial growth, leading to significant heavy metal pollution and severe environmental impacts. Although public awareness of environmental pollution increased during the 1990s, leading to the implementation of various environmental protection policies, heavy metals remain among the most persistent contaminants in marine systems. Once introduced into coastal waters, these elements are accumulated in marine sediments over time, making sedimentary records valuable indicators for reconstructing historical pollution trends.

The Taiwan Strait is a shallow continental shelf system in which tidal currents play a crucial role in sediment erosion and transport. Sediments in the strait are expected to contain modern fluvial inputs derived primarily from rivers in western Taiwan, which are subsequently transported northward by prevailing coastal currents. Our primary objective is to reconstruct the historical evolution of heavy metal contamination in the Taiwan Strait sediments and to evaluate the influence of industrial development and environmental regulations on observed geochemical trends.

Sediment cores were collected from nearshore to offshore environments in the Taiwan Strait to capture spatial variability associated with sediment transport processes. The ²¹⁰Pb dating, grain size, and geochemical analyses (Zn, Cr, Pb, Co, Ni, Cu, Cd, Fe, Mn, Al, K) were applied to sediment cores. The ²¹⁰Pb activity is used to determine sedimentation rates and constrain sediment ages. Grain-size data were integrated with geochemical results to distinguish between pollution signals and natural sedimentological influences. We assumed that the records show increased heavy metal levels associated with the start of industrial activity, followed by a decrease in the late 1990s due to the enforcement of environmental policies such as the ban on leaded gasoline. The findings provide important insights into the effectiveness of domestic regulations in controlling heavy metal pollution. Moreover, these results suggest that regulations can significantly reduce marine pollution, as evidenced by the decline in pollution levels in Manila Bay following the implementation of stricter environmental laws. Overall, this study demonstrates that marine sediments are powerful archives for tracking pollution histories and play a critical role in environmental management, contributing to the future marine environments.