129I record of nuclear activities in marine sediment core from Jiaozhou Bay in China

Abstract

Iodine-129 has been used as a powerful tool for environmental tracing of human nuclear activities. In this work, a sediment core collected from Jiaozhou Bay, the east coast of China, in 2002 was analyzed for 129I to investigate the influence of human nuclear activities in this region. Significantly enhanced 129I level was observed in upper 70 cm of the sediment core, with peak values in the layer corresponding to 1957, 1964, 1974, 1986, and after 1990. The sources of 129I and corresponding transport processes in this region are discussed, including nuclear weapons testing at the Pacific Proving Grounds, global fallout from a large numbers of nuclear weapon tests in 1963, the climax of Chinese nuclear weapons testing in the early 1970s, the Chernobyl accident in 1986, and long-distance dispersion of European reprocessing derived 129I. The very well 129I records of different human nuclear activities in the sediment core illustrate the potential application of 129I in constraining ages and sedimentation rates of the recent sediment. The releases of 129I from the European nuclear fuel reprocessing plants at La Hague (France) and Sellafield (UK) were found to dominate the inventory of 129I in the Chinese sediments after 1990, not only the directly atmospheric releases of these reprocessing plants, but also re-emission of marine discharged 129I of these reprocessing plants in the highly contaminated European seas.