Behaviours of 210Pb and 137Cs in Yellow Sea Sediments Under the Influence of Waste Dumping

This study presents and evaluates the distribution patterns and deposition fluxes of both natural and artificial radionuclides, ²¹⁰Pb and ¹³⁷Cs, in the sediments of the Yellow Sea region. Higher sediment deposition fluxes of ²¹⁰Pb were observed in the muddy sediment area compared to the sandy area. In addition, the deposition fluxes of excess ²¹⁰Pb at the dumping site and surrounding areas showed higher values (663.1 ± 588.6 Bq/m² yr⁻¹) than those at the non-dumping sites (359.7 ± 373.3 Bq/m² yr⁻¹) within the muddy area. Thus, although the sedimentation rates in the study area calculated using excess ²¹⁰Pb showed an average value of 0.35 ± 0.23 cm yr⁻¹, which is comparable with those reported in previous studies of the Yellow Sea, this study indicates the significant influence of anthropogenic waste dumping on the accumulation of ²¹⁰Pb in the bottom sediments. The ¹³⁷Cs activities in most stations exhibited an exponential decrease from the surface sediments, similar to the pattern of ²¹⁰Pb, although one site showed peak values at depths of 9–13 cm. However, unlike the typical ¹³⁷Cs peaks that correspond to major events, such as the 1963 nuclear tests, the age of the sediments at peak depths in this study ranged widely, from the 1950s to the 1970s. This imprecision in dating is likely attributable to the high sediment turbulence in the Yellow Sea and the weaker particle-reactive nature of ¹³⁷Cs, which facilitates the remobilization of particulate ¹³⁷Cs into the dissolved phase. Moreover, our results indicate a much lower deposition flux of ¹³⁷Cs compared to previous studies, further demonstrating the limitations of using ¹³⁷Cs as a tracer in high-sediment-surface areas. Overall, this study highlights the impact of waste dumping on the accumulation of ²¹⁰Pb in marginal seas, even in dynamic sedimentary environments such as the Yellow Sea.