Plutonium isotopes and radionuclides in corals around Weizhou land in Beibu Gulf, China

Assessment of the depositional characteristics of the Yellow River estuary from 1960s by 239+240Pu and 137Cs

The spatial and vertical distribution of 239+240Pu and 137Cs in the sediments of the Yellow River Delta was studied to evaluate the deposition dynamics in the Yellow River estuary from 1960s. The activity of 239+240Pu and 137Cs in sediment core ranged from 0.001 to 0.212 Bq/kg and 0.52-2.53 Bq/kg, respectively. A maximum accumulation peak and two secondary accumulation peaks appeared in the sediment core YR2. The average deposition rate of 8.3 cm/y for the Yellow River estuary from 1964 to 1976 was obtained. The proportion of Pu from the Yellow River net input and direct deposition to the total inventory of Pu in the estuary was assessed, with a total inventory of Pu in the abandoned estuary of 7.4 × 1010 Bq and a net input of 2.2 × 1010 Bq from the Yellow River. Pu deposited in the estuary only accounts for 18 % of the total Pu transported by the Yellow River, and most of the Pu is injected into the Bohai Sea with the Yellow River.

Radioactivity research in mosses from typical Karst Regions in Leye Tiankeng, Southern China

Radionuclides in environmental ecosystems have ecotoxicity and health impact on human and environment, so radioactive contamination has always been one of the global concerns. This study mainly focused on the radioactivity of mosses collected from the Leye Tiankeng Group in Guangxi. The activities of ^239+240Pu measured by SF-ICP-MS and ¹³⁷Cs measured by HPGe in moss and soil samples are as follows: 0-2.29 Bq/kg in mosses and 1.5-11.9 Bq/kg in soils for ¹³⁷Cs, and 0.025-0.25Bq/kg in mosses and 0.07-0.51Bq/kg in soils for ^239+240Pu. The range of ²⁴⁰Pu/²³⁹Pu atom ratios (0.201 in mosses and 0.184 in soils) and ^239+240Pu/¹³⁷Cs activity ratios (0.128 in mosses and 0.044 in soils) indicated that the ¹³⁷Cs and ^239+240Pu in study area were mainly contributed by global fallout. ¹³⁷Cs and ^239+240Pu showed similar distribution in soils. However, their behaviors in mosses were quite different due to the differences in the growth environment of mosses. The transfer factors of ¹³⁷Cs and ^239+240Pu from soil to moss varied in different growth stages and specific environments. A weak positive correlation among ¹³⁷Cs, ^239+240Pu in mosses and soil-derived radionuclides suggested that resettlement was predominant here. The negative correlation between ⁷Be, ²¹⁰Pb and soil-derived radionuclides indicated that ⁷Be and ²¹⁰Pb came from atmospheric components, while the weak correlation between them suggested that their specific sources were different. The Cu and Ni were moderately enriched in mosses here due to the use of agricultural fertilizers, At the same time, Zn was at a high level in the Lilang area, where transportation was more developed.

Plutonium isotopes in the northwestern South China Sea: Level, distribution, source and deposition

The spatial distribution of plutonium isotopes (²³⁹Pu, ²⁴⁰Pu) in the surface sediments collected from the northwestern South China Sea (SCS) in 2018 was investigated. The ^239,240Pu concentrations in surface sediments vary from 0.048 to 0.960 mBq/g (with mean of 0.282 ± 0.242 mBq/g) depending on the geographical feature of the sampling location such as the river estuary, continental shelf, slope and deep basin. Higher ²⁴⁰Pu/²³⁹Pu atomic ratios (0.24-0.31) in the surface sediment of the SCS compared to the global fallout value of 0.18 were observed, this is attributed to the input of close-in fallout of the Pacific Proving Ground (PPG) transported by the North Equatorial Current and Kuroshio Current to the northern SCS. The contribution of the PPG derived plutonium in the SCS sediment was estimated to be 39%-78% using a simple two-end member mixing model based on the measured ²⁴⁰Pu/²³⁹Pu atomic ratios in the sediment. Besides the soluble ^239,240Pu level in seawater, load of suspended particulate matter from the river runoff and biological debris, hydrographic and hydrodynamic conditions are key parameters influencing the deposition process of plutonium to the sediment.