Historical trends of styrene oligomers in core sediments from the intertidal zone of the Yellow Sea and Bohai Seas

Historical trends of styrene oligomers (SOs) in sediments from intertidal zones of the Yellow and Bohai Seas were investigated for the first time. In South Korea, SO concentrations (4.82–12.0 ng g⁻¹ organic carbon (OC)) peaked during the 1990s and declined thereafter, reflecting the indirect effects of enhanced environmental regulations. In contrast, Chinese coastal regions exhibited relatively stable SO levels (1.48–20.5 ng g⁻¹OC) until the 1990s, followed by significant increases after the early 2000s. Consistently low styrene dimer-to-trimer ratios observed in Chinese sediments since 2000 indicate continuous fresh inputs of SOs. Furthermore, increasing SO concentrations and fluxes in China significantly correlated with rising national polystyrene production, suggesting the potential for continued future increases without effective controls. Conversely, the persistent decline of SO concentrations observed in surface sediments from Korean waters over the past two decades highlights the effectiveness of environmental policy interventions.