Pu and¹³⁷Cs in the Yangtze River Estuary Sediments: Distribution and Source Identification

Abstract

Pu isotopes and (137)Cs were analyzed using sector field ICP-MS and γ spectrometry, respectively, in surface sediment and core sediment samples from the Yangtze River estuary. (239+240)Pu activity and (240)Pu/(239)Pu atom ratios (>0.18) shows a generally increasing trend from land to sea and from north to south in the estuary. This spatial distribution pattern indicates that the Pacific Proving Grounds (PPG) source Pu transported by ocean currents was intensively scavenged into the suspended sediment under favorable conditions, and mixed with riverine sediment as the water circulated in the estuary. This process is the main control for the distribution of Pu in the estuary. Moreover, Pu is also an important indicator for monitoring the changes of environmental radioactivity in the estuary as the river basin is currently the site of extensive human activities and the sea level is rising because of global climate changes. For core sediment samples the maximum peak of (239+240)Pu activity was observed at a depth of 172 cm. The sedimentation rate was estimated on the basis of the Pu maximum deposition peak in 1963-1964 to be 4.1 cm/a. The contributions of the PPG close-in fallout Pu (44%) and the riverine Pu (45%) in Yangtze River estuary sediments are equally important for the total Pu deposition in the estuary, which challenges the current hypothesis that the riverine Pu input was the major source of Pu budget in this area.

Isotopic Composition and Distribution of Plutonium in Northern South China Sea Sediments Revealed Continuous Release and Transport of Pu from the Marshall Islands

“…17,18 The calculated results showed the contributions to the northern SCS shelf from the PPG were 62% ± 13%−87% ± 7% (78% ± 2%) if R P equaled 0.30 and 46% ± 10%−65% ± 6% (58% ± 2%) if R P equaled 0.36. Overall, the average contribution from the PPG was 68% ± 1% in the northern SCS shelf, which was higher than similar estimates made for the SCS basin (∼57%), 30 East China Sea (∼45%), 24,25 Japan Sea (∼20%), 27 and western North Pacific off the eastern coast of Japan (∼40%). 52 In the PRE, the PPG contribution was estimated to be 30% ± 5%, significantly lower than that in the SCS shelf.…”

Temporal and vertical distributions of anthropogenic 236U in the Japan Sea using a coral core and seawater samples

“…Assuming that this hypothesis is correct, resuspension of offshore bottom sediments with the outflow from this river could be conceivable. These bottom sediments in the East China Sea should contain Pu predominantly after starting the nuclear tests [Liu et al, 2011].…”

Distribution of Pu isotopes in marine sediments in the Pacific 30 km off Fukushima after the Fukushima Daiichi nuclear power plant accident

“…In the western North Pacific, the principal sources of Pu are: (1) the close-in tropospheric fallout from nuclear weapons testing at the Pacific Proving Ground (PPG) in the Marshall Islands which has a high 240 Pu/ 239 Pu ratio of 0.33-0.36; and (2) the global fallout Pu with a 240 Pu/ 239 Pu ratio of 0.18 (Bowen et al, 1980;Diamond et al, 1960;Livingston and Povinec, 2002;Kelley et al, 1999). Over the past years, the distributions of Pu isotopes in the western North Pacific and its marginal seas have been intensively studied to understand their fate and transport in the marine environment and to explore the potential applications as geochemical tracers to understand a variety of marine and oceanic processes (Bertine et al, 1986;Buesseler, 1997;Dong et al, 2010;Hirose et al, 2007;Kim et al, 2004;Lee et al, 2004Lee et al, , 2005Liu et al, 2011a;Norisuye et al, 2006;Okubo et al, 2008;Wang and Yamada, 2005;Yamada et al, 2006;Zheng and Yamada, 2004, 2005, 2006b, 2006c. These studies provide useful background data for the estimation of possible Pu contamination due to the Fukushima DNPP accident.…”