Historical trends of polychlorinated biphenyls and alkylphenols recorded in core sediments from the intertidal areas of the Yellow Sea and Bohai Sea

Historical records of polychlorinated biphenyls (PCBs) and alkylphenols (APs) were reconstructed from intertidal zones of the Yellow and Bohai Seas over the past 80 years. Concentrations of PCBs (1.50-6.47 ng g^-1 organic carbon (OC)) and APs (8.42-13.8 ng g^-1 OC) in Dangjin, South Korea, peaked in the 1970s and subsequently declined. Conversely, levels in Tianjin and Dandong, China, have continued to increase in recent decades (PCBs: 0.53-6.1 ng g^-1 OC; APs: 2.61-42.7 ng g^-1 OC). These divergent trends align with regulatory enforcement: levels in South Korea declined following the implementation of regulations in 1979 and 2003, while the continued increase in China, despite regulation in 1974 and 2011, points to unregulated sources. Estimated fluxes of PCBs and APs from the intertidal zone to offshore areas decreased by approximately 83% and 57%, respectively. This study provides baseline data for assessing long-term pollution trends in intertidal environments.