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

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.