Iodine isotopes (I and I) in the hydrosphere of Qinghai-Tibet region and South China Sea.

The radioactive isotope I, with a half-life of 1.57 × 10 years, is widely used as a tracer to assess nuclear safety, to track environmental and geological events and to figure out the details of the stable iodine geochemical cycle. This work investigated the I and I distribution in water samples collected from the terrestrial (rivers, lakes and springs) and marine water systems (estuary and sea) in China. The measured I concentrations of (1-51) × 10 atoms/L and I/I ratios of (0.03-21) × 10 shows the variability of I level in the water systems. The local permafrost and seasonal frozen environment play a key role in groundwater recharge in the Qinghai-Tibet region, which is reflected in the I distribution in surface water. The depth distribution of I in the water column of the South China Sea reflects the effluence of different currents. The results also indicate that the hydrosphere of China contains one to three orders of magnitude less I compared to those reported in Europe. Despite the large distance, the European nuclear fuel reprocessing facilities represent the major source of I in the hydrosphere of China through atmospheric transport. The contribution of the Fukushima nuclear accident to I levels in the hydrosphere of China was negligible.