237Np and 241Am as Fingerprints in the Major River Basins of Southern China and North South China Sea: A Land-Sea Perspective

Presence of 236U,237Np and 239,240Pu in shells from the coast of the south of China

This study reports first results on uranium (236U), neptunium (237Np) and plutonium (239Pu and 240Pu) isotopes in shell samples (i.e. oyster, clam and scallop shells) from the coast of the South of China. The 240Pu/239Pu and 236U/238U atom ratios are used for source identification, and the 237Np/239Pu, 237Np/236U and 236U/239Pu non-isotopic atom ratios to study the relative bioaccumulation of Np, Pu and U during the shell formation. The obtained concentration levels are in the 104-106 atoms g-1 range in every case. Clear regional differences are observed in the case of the 240Pu/239Pu atom ratio, with average values lower along the coast of East China Sea (average 0.227 ± 0.120, n = 5) compared to the South China Sea (average 0.258 ± 0.018, n = 7), showing a possible influence of the Pu released at the Pacific Proving Ground nuclear test site. 236U/238U ( × 10-8) atom ratios range from 0.046 ± 0.009 to 0.524 ± 0.135, in agreement with the expected levels in surface seawater from the China Sea. 237Np/239Pu (average 4.1 ± 2.6, n = 13) and 237Np/236U ratios (average 14 ± 10, n = 13) in the oyster shells are clearly enhanced compared to the estimated one in the surface seawater, pointing out higher bioaccumulation of Np compared to Pu and U.

Spatial distribution and modelling of 239+240Pu in the sediments and seawater columns of the South China Sea and Indian Ocean

In order to investigate the 239+240Pu potential influence in the ocean, and develop a new method for rapidly monitoring radioactive pollution, the 239+240Pu spatial distribution in the South China Sea (SCS) and the Indian Ocean (IND) sediments is analyzed by SF-ICP-MS (ELEMENT 2). The inventory-weighted mean activities of 239+240Pu were 0.413 ± 0.333 mBq/g, 0.128 ± 0.044 mBq/g, and 0.483 ± 0.606 mBq/g in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The 239+240Pu activity spatial distribution in the SCS sediments was influenced by the current, the vertical distribution of Pu in seawater, and the transport of particulate matter. The 239+240Pu activity spatial distribution in the IND sediments could be impacted by Antarctic Intermediate Water. The average of 240Pu/239Pu atomic ratios were 0.258 ± 0.034, 0.219 ± 0.031, and 0.212 ± 0.028 in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The 240Pu/239Pu atomic ratios in the SCS and IND indicate that Pu from the Pacific Proving Ground (PPG) is transported to the IND via the SCS internal current and transverse ocean currents within Indonesia. In addition, a seawater advection-dispersion equation (S-ADE) model is established based on the actual physical processes of radionuclides in the seawater column and well fitting results were obtained (R2 = 0.49 to 0.99). The 239+240Pu data and the geographic information from the sample site were used to correct the Pu distribution in the seawater. The calculated 239+240Pu mean concentrations in the surface seawater were 2.465 mBq/m3 and 2.205 mBq/m3 for the SCS and the eastern IND seawater, respectively, and the result is consistent with the previous measurements. Then, the 239+240Pu stored in the study area of SCS and eastern IND was estimated to be approximately 1.0-1.4% of the global ocean based on the model. This study provides a useful model for guiding and designing future monitoring of pollution by anthropogenic Pu and other isotopes.

Spatial variation, sources, and potential ecological risk of metals in sediment in the northern South China Sea

Heavy metals are of great concern to humans because of their persistence, bioaccumulation, and toxicity. A study on the spatial variation, sources, and potential ecological risk of heavy metals in the coastal sedimentary environment are helpful to clarify the pollution history of aquatic systems and effectively manage and control heavy metal pollution. However, most studies are limited to the Pearl River Estuary region. To investigate the spatial distribution characteristics, sources, and potential ecological risks of heavy metals (Cr, Cu, Pb, Ni, Sn, Zn, As, Cd), a total of 41 sediment samples from the northern South China Sea (NSCS) region were analyzed. The results show that Cu, Ni, Pb, and Zn have similar distribution patterns and their migration path in the coastal area is mainly controlled by the coastal current in western Guangdong. Meanwhile, these metals also have similar sources, i.e. natural weathering products. The distribution patterns of Cr, Sn, Cd, and As are not affected by the coastal current, and the sources of these metals are not only natural weathering products but also human inputs such as electroplating and electronic industries and runoff from agricultural sites. Agricultural activities, coal-burning activities, and aerosol precipitation may be another important source of human activities for As. More than half (65.9 %) of the sampling sites were categorized as having low potential ecological risk, 24.4 % for moderate risk, 7.3 % for considerable risk, and 2.4 % for high potential ecological risk, and the potential ecological risk metals of Cr, Cd, and As in NSCS should be more attention.