Vertical Distributions of Radionuclides (^239+240Pu, ²⁴⁰Pu/²³⁹Pu, and ¹³⁷Cs) in Sediment Cores of Lake Bosten in Northwestern China

Artificial radionuclides (¹³⁷Cs, ^239+240Pu, ²⁴¹Pu, ²⁴¹Am) deposited in lacustrine sediments have been used for dating as well as radionuclide source identification. In the present work, we investigated the vertical distributions of ^239+240Pu and ¹³⁷Cs activities, ²⁴⁰Pu/²³⁹Pu atom ratios, and ^239+240Pu/¹³⁷Cs activity ratios in sediment cores collected from Lake Bosten, which is the lake closest to the Lop Nor Chinese Nuclear Weapon Test site in northwestern China. Uniformly high concentrations of ^239+240Pu and ¹³⁷Cs were found in the upper layers deposited since 1964 in the sediment cores, and these were controlled by the resuspension of soil containing radionuclides from the nearby land surface. As the Chinese nuclear tests varied remarkably in yield, the mixing of the tropospheric deposition from these tests and the stratospheric deposition of global fallout has led to a ²⁴⁰Pu/²³⁹Pu atom ratio that is similar to that of global fallout and to a ^239+240Pu/¹³⁷Cs activity ratio that is slightly higher than that of global fallout. However, a low ²⁴⁰Pu/²³⁹Pu atom ratio of 0.080 and high ^239+240Pu/¹³⁷Cs activity ratio of 0.087, significantly different from the global fallout values, were observed in one sediment core (07BS10-2), indicating the inhomogenous tropospheric deposition from the Chinese nuclear tests in Lake Bosten during 1967–1973. These results are important to understand the influence of the CNTs on the radionuclide contamination in Lake Bosten

Peroxygenase activity of OxdAs (WT and H320D).

<p>Peroxygenase activity of OxdAs (WT and H320D).</p

Analyses of peroxidase activities of OxdAs in the presence of ABTS.

<p>(A) The peroxidase activities of OxdAs depending on the H₂O₂ concentration. OxdA(WT) [(a) black circles], OxdA(H320D) [(a) black triangles], and OxdA(H320A) [(b) black square]. (B) Michaelis—Menten kinetics of the peroxidase activity of OxdAs. OxdA(WT) (a), OxdA(H320D) (b) and OxdA(H320A) (c). The reactions with ABTS as a substrate were carried out under the “standard assay C” conditions as described under “Materials and Methods.” For all data points, values are means ± mean error.</p

Peroxidase activity of OxdAs using guaiacol as a substrate.

<p>Peroxidase activity of OxdAs using guaiacol as a substrate.</p

Peroxidase activity of OxdAs using ABTS as a substrate.

<p>Peroxidase activity of OxdAs using ABTS as a substrate.</p

Analyses of peroxidase activities of OxdAs in the presence of guaiacol.

<p>(A) The peroxidase activities of OxdAs depending on the H₂O₂ concentration. OxdA(WT) [(a) black circles], OxdA(H320D) [(a) black triangles], and OxdA(H320A) [(b) black square]. (B) Michaelis—Menten kinetics of the peroxidase activity of OxdAs. OxdA(WT) (a), OxdA(H320D) (b) and OxdA(H320A) (c). The reactions with guaiacol as a substrate were carried out under the “standard assay B” conditions as described under “Materials and Methods.” For all data points, values are means ± mean error.</p

Michaelis—Menten kinetics of the catalase activity of OxdAs.

<p>The reactions were carried out under the “standard assay A” conditions as described under “Materials and Methods.” For all data points, values are means ± mean error. OxdA(WT) (A), OxdA(H320D) (B) and OxdA(H320A) (C).</p

Catalase activity of OxdAs (WT, H320D and H320A).

<p>Catalase activity of OxdAs (WT, H320D and H320A).</p

Contribution of radionuclide to dose rate estimated on expressway from Fukushima Prefecture to Aomori Prifecture.

<p>*FNPS: Fukshima Dai-ichi Nuclear Power Station.</p

Cumulative individual radiation dose accumulated daily.

<p>The survey teams have started measuring our departure from Hirosaki.</p