What Anthropogenic Radionuclides (90Sr and 137Cs in Atmospheric Deposition, Surface Soils and Aeolian Dusts Suggest for Dust Transport over Japan

Abstract

Currently, atmospheric anthropogenic radionuclides (particulate) are controlled by suspension of the surface dust containing those radionuclides (resuspension). We have found, therefore, that such radionuclides can be used as tracers of the surface dust suspension, transport and its subsequent deposition in distant areas. The 137 Cs/ 90 Sr activity ratios in the atmospheric deposition, without the direct influence of nuclear tests and accidents, at the Meteorological Research Institute (MRI, Tsukuba, Japan) during the 1990s were fairly low (average: 2.1). This value is not in agreement with the ratios in Japanese surface soils (range of averages: 4-7), which had been considered as the primary source of the deposited dust. This suggests that the current atmospheric dust deposition in Japan is a mixture of local and remote components. The remote component could be an aeolian dust that has been transported long distances from arid areas. The major component is most likely to be Asian dust. It was further hypothesized that other remote source may exist beyond the Asian domain, based on accumulated observations and model results. To obtain more information about the dust transport, Sahara dust deposited in Monaco in 2002 and a suspended dust collected in the Taklamakan area in 2001 were analyzed for 90 Sr and 137 Cs. The Taklamakan dust exhibited a 137 Cs/ 90 Sr ratio of about 4, which is within the range of atmospheric deposition observed at the MRI, while the Sahara dust exhibited a higher 137 Cs/ 90 Sr ratio (about 13). Although the present Sahara datum was negative for our hypothesis of 'hyper-range transport', the seasonal change of the 137 Cs/ 90 Sr ratio in the atmospheric deposition observed at the MRI requires an aeolian dust source having a low 137 Cs/ 90 Sr ratio, other than Asian dust.

The seasonal variations of atmospheric 134,137Cs activity and possible host particles for their resuspension in the contaminated areas of Tsushima and Yamakiya, Fukushima, Japan

“…In general, water-soluble cesium ions from SO 4 2− are considered to be adsorbed or attached to mineral particles in a soil environment (Bostic et al 2002;Dumat and Staunton 1999;Mukai et al 2014). These mineral particles were shown to act as resuspended host particles in an atmospheric environment by the previous investigations of the global fallout from atmospheric nuclear weapon tests (e.g., Igarashi et al 2005;Masson et al 2010). Therefore, a major resuspension source has been thought to be the suspension of contaminated dust particles by wind Ishizuka et al 2017;Sýkora et al 2012), even for the case of the FDNPP accident contamination.…”

“…Many studies have indicated that 137 Cs is firmly adsorbed to clay mineral particles (e.g., Dumat and Staunton 1999;Igarashi et al 2005;Masson et al 2010;Mukai et al 2014;Ishizuka et al 2017), and the transport of mineral dust particles by wind is considered to be a significant resuspension process. As shown in Fig.…”

Change of the Asian dust source region deduced from the composition of anthropogenic radionuclides in surface soil in Mongolia

“…The 90 Sr and 137 Cs specific activities and the 137 Cs/ 90 Sr ratio of the Mongolian soil are summarized in Table 1 together with previously published values for surface soil and atmospheric total (wet + dry) deposition (Igarashi et al, 2005(Igarashi et al, , 2009. The data were decay-corrected as of fall 2007, the time the soil samples were collected in Mongolia.…”

“…137 Cs contamination detected in France during a Saharan dust event was suspected to be the result of leakage from past nuclear test sites in French Saharan territory (Danesi et al, 2008). Igarashi et al (2005) pointed out that close-in fallout from atmospheric nuclear explosions should have been an insignificant source of surface contamination of 90 Sr and 137 Cs around the test sites, thus negligible in aeolian dust transport; and French researchers drew similar conclusions (Menut et al, 2009;Masson et al, 2010). Only 0.7 % of the Saharan dust was ascribed to the test area, accounting for only a small percentage of the atmospheric 137 Cs peak concentrations recorded in France during the transport event (Menut et al, 2009).…”

“…In addition, the possibility of an eastward expansion of the source of Asian dust was suggested by Kurosaki and Mikami (2003) and Lim and Chun (2006) and later confirmed by Kim (2008). We have been investigating features of the continental and local dust sources using 90 Sr and 137 Cs, which are anthropogenic radionuclides contained in the surface soil with half-lives of 30 years (Igarashi, 2004(Igarashi, , 2009aIgarashi et al, 2001Igarashi et al, , 2005Igarashi et al, , 2006Igarashi et al, , 2009Fukuyama and Fujiwara, 2008;Fujiwara, 2010;Fujiwara et al, 2007).…”