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 nonisotopic 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 ( x 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.