Historical record of nuclear activities from (129)I in corals from the northern hemisphere (Philippines).

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Historical record of nuclear activities from (129)I in corals from the northern hemisphere (Philippines).

J Environ Radioact. 2016 Nov;164:174-181

Authors: Bautista AT, Matsuzaki H, Siringan FP

Abstract
Iodine-129 is a long-lived fission product that is majorly released in human nuclear activities (HNA) such as nuclear bomb testing, nuclear fuel reprocessing, and nuclear accidents. It is a good environmental tracer and former measurements of (129)I in corals from the southern hemisphere show the increasing trend of (129)I concentrations in the marine environment caused by HNA. Here we show time series of (129)I/(127(stable))I isotopic ratios in two coral cores from the northern hemisphere (Philippines) and how these record (129)I released from HNA in even greater, unprecedented detail. Corals were taken from the Pacific Ocean (Baler) and South China Sea (Parola) sides of the Philippines. We observed nearly identical peaks ((129)I/(127)I ∼ 31.5 × 10(-12)) in both the Baler and Parola records, each attributed to the year 1962 - the year with the highest recorded amount of (129)I release from nuclear bomb testing. This 1962 (129)I bomb signal offers a new time marker that can be used to establish or confirm age models of corals, comparable to or possibly better than the well-known coral (14)C bomb peak. We also observed nuclear fuel reprocessing and Chernobyl accident (129)I signals in years 1977, 1980, and 1986, concurrently in Parola and with 9 to 11-year lags in Baler. This discrepancy in timing suggests that (129)I was transported to the South China Sea and Pacific Ocean sides of the Philippines directly from the atmosphere and through prevailing ocean currents, respectively. Lastly, we observed surprisingly high (129)I/(127)I isotopic ratios (i.e., 22.8 to 38.9 × 10(-12)) in the Parola record after the year 1996, which is in contrast to the decreasing trend observed in the Baler record and in published (129)I releases of different HNA. These results possibly indicate the presence of unknown sources of (129)I in the South China Sea region.

PMID: 27494290 [PubMed - indexed for MEDLINE]

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