Desorption Behavior of Fukushima-derived Radiocesium in Sand Collected from Yotsukura Beach in Fukushima Prefecture

Abstract

Beach sand samples were collected along a coastal area 32 km south of the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Fukushima Prefecture, Japan, 5 years after the FDNPP accident. Desorption experiments were performed on the sand samples using seawater in a batch experimental system to understand the forms of existence of radiocesium in sand and their desorption behavior in a coastal environment. The percentage of radiocesium desorption decreased exponentially with an increase in the number of desorption experiments for the four sand samples, with 137 Cs radioactivity from 16 to 1077 Bq kg-1 at surface and deeper layers from three sites. Total desorption percentage ranged from 19 to 58% in 12 desorption experiments. The results indicate that the weak adsorption varies with the sampling sites and their depth layer. To understand the desorption behavior of radiocesium in the sand samples, the desorption experiments were performed for a sand sample by using natural and artificial seawater, and NaCl solution in the presence and absence of KCl. The 137 Cs desorption from the sand collected at a depth of 100-105 cm from the ground surface (137 Cs radioactivity 1052 ± 25 Bq kg-1) was 0.1% by ultrapure water, 3.7% by 1/4 seawater and 7.1% by 1/2 seawater, 2.2% by 470 mM NaCl solution (corresponding to a similar concentration of seawater) and 10-12% by seawater, artificial seawater and 470 mM NaCl + 8 mM KCl solution. These results indicate that about 10% of radiocesium adsorbed on the sand is mainly desorbed by ion exchange of potassium ion in seawater, though the concentration of major cation, or sodium ion, in seawater makes a small contribution on 137 Cs desorption from the sand samples.

Behavior of Radiocesium in Sediments in Fukushima Coastal Waters: Verification of Desorption Potential through Pore Water

“…6,7 It is also reported that sand at the beach near Fukushima retains radiocesium and exchanges it with pore water having a relatively long residence time to increase the radiocesium concentration in the pore water. 8,9 Uptake of cesium in crystal lattices in clay minerals, especially illite, is basically irreversible in freshwater systems, but it is well established that some proportion of cesium is desorbed in high ionic strength media such as seawater. 10,11 Feldspar has a small adsorption capacity, but due to its abundance in the coastal environment, it is considered that a large amount of radiocesium is incorporated into sandy sediments.…”

“…The major deposition of radiocesium on the seabed can be explained by the adsorption of dissolved radiocesium on the seabed in the early stage of the accident. , The influx of particulate radiocesium from rivers has increased its contribution as a transport process of radiocesium to the seabed of the Fukushima coast, especially in recent years . On the Fukushima coast, it has been pointed out that about several to 30% of radiocesium in riverine suspended particles desorbs when the particles mixed with seawater. , It is also reported that sand at the beach near Fukushima retains radiocesium and exchanges it with pore water having a relatively long residence time to increase the radiocesium concentration in the pore water. , …”

Suspended Particle–Water Interactions Increase Dissolved 137Cs Activities in the Nearshore Seawater during Typhoon Hagibis

“…It is noted that even if the desorbed fraction (light blue color bars) was deducted from the observed dissolved 137 Cs activity, the remaining dissolved 137 Cs activity at each station was still higher than that in offshore water during the high-flow condition (pre-typhoon, Figure 6). For example, stations S4 and S6 were close to Yotsukura, Iwaki City, Fukushima Prefecture where it has been reported that the input of 137 Cs to the dissolved phase in seawater through the SGD 16,47 contributed the higher dissolved 137 Cs concentration. Therefore, the contribution of the desorption process heightening dissolved 137 Cs concentration in the nearshore water during the high-river-flow period of June−September 2019 may have been less intense.…”

Operational Method to Easily Determine the Available Fraction of a Contaminant in Soil and the Associated Soil-Solution Distribution Coefficient

“…In order to demonstrate the benefits of this method to the scientific community, works in which enough information was available to be reinterpreted or, for which authors provided complementary information, have been selected. The works conducted by Zheng and Wan (2005), 15 Elias et al (2003), 22 Nagao et al (2020), 23 and Rigol et al (1999) 11 have been reinterpreted using our proposed method. The experimental protocols used by the authors to acquire their data are described here.…”