Determination and Assessment of Transuranic Isotopes (Pu, Np, Am) Activities and Isotopes Ratios in Antarctic Marine Sediments

• Published in: ACS earth and space chemistry Vol. 5; no. 12; pp. 3488 - 3498
• Main Authors: Han, Xibin, Han, Xiaoxiao, Li, Zhihong, Liu, Zhiyong, Zhang, Yongcong, Hu, Liangming
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16.12.2021
• Subjects: Marine sediments; Americium; Antarctica; Plutonium; Neptunium
• ISSN: 2472-3452; 2472-3452
• DOI: 10.1021/acsearthspacechem.1c00314

Due to the nuclear testing in the 20th century, a considerable amount of anthropogenic transuranic isotopes (237Np, 239, 240Pu, and 241Am) was produced, spread, and deposited in the natural environment including Antarctica. Here, activities of 239+240Pu, 237Np, and 241Am in Antarctic marine sediments are determined by ICP-SF-MS, ranging from 0.008 to 0.293 Bq/kg for 239+240Pu, from 0.057 to 0.926 mBq/kg for 237Np, and from 0.027 to 0.277 Bq/kg for 241Am. The dominant source of 237Np, 239, 240Pu, and 241Am in the study marine sediments is global fallout. 240Pu/239Pu atom ratio is measured to be 0.179 ± 0.010 (n = 17) on average, which is consistent with the global fallout of the nuclear weapons tests. Average 237Np/239Pu atom ratio for global fallout is suggested as 0.221 (n = 58), which may be used as a new characteristic index to indicate the current source of Np in a certain region. Due to the different fractionations of Pu and Am by seawater and the enrichment efficiency of marine particles, 241Am/239+240Pu activity ratios in these samples (mean, 2.037 ± 0.040; n = 17) are much higher than global fallout. In addition, 237Np/239Pu atom ratio and 241Am/239+240Pu activity ratio are found to be positively correlated with the sampling depth. Furthermore, the correlation between organic matter and eight heavy metals with transuranic activities is revealed. The cold climate, latitude, and sediment properties have an important influence on the distributions of Np, Pu, and Am in these marine sediments of Antarctic.