New study maps radioactive pollutant transport in northern South China Sea
by Riko Seibo
Tokyo, Japan (SPX) Oct 24, 2025

Researchers from the Institute of Earth Environment, Chinese Academy of Sciences have analyzed the movement and spread of radioactive iodine isotopes in the northern coastal region of the South China Sea, an area with a high concentration of nuclear power plants. Leading the study, Jinxiao Hou, Dr. Xiaolin Hou, and Dr. Yanyun Wang used comprehensive seawater sampling and ultra-trace analytical techniques to measure concentrations and spatial distributions of 129I and 127I isotopes.

Their findings clarify how the 129I/127I atomic ratio reveals the transport and dispersion mechanisms of anthropogenic radionuclide 129I. Riverine sources supply most of the 129I within estuarine and nearby coastal waters, but their effect is restricted to about 100 km from river mouths and the upper 10 meters of the water column. Quantitative source analysis indicates ocean currents contribute the most to the 129I levels, followed by river input and direct fallout from the atmosphere.

During the summer, southwest monsoon patterns force surface 129I into a fan-shaped distribution over the Pearl River estuarine shelf, limiting southward movement and offshore spread of the plume. The buoyancy of freshwater and local upwelling restrict vertical mixing of 129I. In offshore areas, depletion near the surface and conservative behavior at sub-surface depths create a pronounced maximum for both 129I concentration and the atomic ratio below the surface. The results establish a scientific framework for predicting the dispersion and impact zones of radionuclide releases in marginal seas and assessing environmental radiation security.

Research Report:Sources, transport, and migration of 129I in the northern South China Sea

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