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 (129)I to investigate the influence of human nuclear activities in this region. Significantly enhanced (129)I 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 (129)I 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 (129)I. The very well (129)I records of different human nuclear activities in the sediment core illustrate the potential application of (129)I in constraining ages and sedimentation rates of the recent sediment. The releases of (129)I from the European nuclear fuel reprocessing plants at La Hague (France) and Sellafield (UK) were found to dominate the inventory of (129)I in the Chinese sediments after 1990, not only the directly atmospheric releases of these reprocessing plants, but also re-emission of marine discharged (129)I of these reprocessing plants in the highly contaminated European seas.

129I and its species in the East China Sea: level, distribution, sources and tracing water masses exchange and movement

“…Compared to plutonium, iodine is water soluble and conservative in ocean, the close-in fallout of 129 I at the PPG can be also transported to the ECS in early time of the NWTs at PPG. The 129 I in the sediment core collected in Jiaozhou Bay in the YS has recorded a small but obvious PPG derived signal of 129 I in 195727. Meanwhile, a similar 129 I peak occurred in 1957–1958 in coral samples collected in the coastal region in Philippine has also been reported30, which suggests that PPG derived 129 I might have a contribution to 129 I in the ECS.…”

“…However, the global fallout of 129 I from all atmospheric NWTs might be one of 129 I sources in the ECS because of the large releases. A relative high 129 I signal of the global fallout peaked in 1962–1963 has been observed in the sediment core collected in the Jiaozhou Bay27. Compared to the direct deposition of 129 I in the ECS in early time of atmospheric NWTs, the leaching of 129 I from the earth surface by rainwater and subsequent transport to the ECS through rivers might be one of important source and pathway of 129 I in the ECS.…”

“…131 I signal in the atmospheric samples collected at northern China in May 1986 immediately after the Chernobyl accident has been observed, and a small signal of Chernobyl accident derived 129 I has been also observed in the sediment collected in the YS27. However, no 131 I in the atmosphere in southern China was observed in 1986 after the Chernobyl accident.…”

“…All NWT sites are far from the ECS and the catchment of rivers flowing into the ECS. The nearest testing site at Lop Nor (41°30′N, 88°30′E) is about 3000 km northwest of the ECS, where only 23 atmospheric NWTs were implemented in 1964–1980, An investigation of a sediment core collected in Jiaozhou Bay in the YS has observed a small but obvious 129 I signal in 1972–1976, which was attributed to the contribution of Chinese NWTs in this period27. Considering the very small 129 I signal of Chinese NWTs in the corresponding layer of this sediment core and these tests were implemented more than 30 years ago, the direct contribution of the Chinese NWTs to the 129 I in the ECS, especially the present surface seawater, should be insignificant.…”

“…Re-emission of the reprocessing derived 129 I from the contaminated seawater to the atmosphere has become a major source of 129 I in the air in recent years32. The 129 I record in the sediment core from the YS has demonstrated that the atmospheric releases of the European NFRPs and re-emission of the reprocessing derived 129 I in the sea is a major source of 129 I in the present sediment in the YC27. 129 I in the Japan Sea was also attributed to the European NFRPs6.…”