Anomalous Plutonium Isotopic Ratios in Sediments of Lake Qinghai from the Qinghai-Tibetan Plateau, China

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• 作者：Fengchang Wu ; Jian Zheng ; Haiqing Liao ; Masatoshi Yamada ; Guojiang Wan
• 刊名：Environmental Science & Technology
• 出版年：2011
• 出版时间：November 1, 2011
• 年：2011
• 卷：45
• 期：21
• 页码：9188-9194
• 全文大小：882K
• 年卷期：v.45,no.21(November 1, 2011)
• ISSN：1520-5851

文摘

The vertical profiles of ^239+240Pu and ¹³⁷Cs activities and ²⁴⁰Pu/²³⁹Pu isotopic ratios are determined for three sediment cores of Lake Qinghai from the Qinghai-Tibetan Plateau, China, and compared with those in sediments of another three lakes (Lakes Bosten, Sugan, and Shuangta), the only existing ones closest to Lop Nor area, China鈥檚 nuclear weapons test site in the northwestern part of the country. The mean inventory of 47.7 卤 18.7 MBq km^鈥? for ^239+240Pu activity in Lake Qinghai is comparable to the average value of global fallout expected at the same latitude, yet the mean inventory of 1112.0 卤 78.0 MBq km^鈥? for ¹³⁷Cs is slightly lower than that of global fallout. Anomalously low ²⁴⁰Pu/²³⁹Pu isotopic ratios (0.038鈥?.125) were found in the 3鈥?.5 cm deep sediment layers, indicating the trace Pu input from early nuclear weapons research activities at Atomic City in the lake鈥檚 watershed during the 1950鈥?0s. Model calculation indicated that the Pu input accounted for approximately 5鈥?6% of the total Pu inventory. The observation of low ²⁴⁰Pu/²³⁹Pu ratio in the deep sediment layer provided a new time marker for recent sediment dating in the lake and around the area. The results are of great significance to the further understanding of sources, records, and environmental impacts of global and regional nuclear activities in the environment and provide important chronological information for further studies on the water eutrophication process and climatic change, and reconstruction of pollution history of organic contaminants and heavy metals in the watershed of Lake Qinghai.