Vertical migration of radiocesium and clay mineral composition in five forest soils contaminated by the Fukushima nuclear accident

Abstract

In forest soils contaminated by radiocesium ( 134 Cs and 137 Cs), deposition from the Fukushima nuclear accident, clay minerals might play important roles in long-term cesium (Cs) dynamics through sorption. To determine whether radiocesium can be retained within the organic layer and the upper mineral soil layers in the Fukushima region, we investigated the vertical distribution of 134 Cs and 137 Cs and the clay mineral composition in five soil profiles of varying radiocesium deposition levels and vegetation types. X-ray diffraction analyses and oxalate extraction suggested that hydroxy-interlayered vermiculites and shortrange-ordered aluminum (Al) and iron (Fe) compounds (i.e, allophane and ferrihydrite) were major clay mineral species of the upper soil layers. The vertical soil distribution of 134 Cs and 137 Cs suggested that most of them were retained in the organic layer and upper mineral soil layer under different levels of deposition. Within 1.5 years after the accident, both 134 Cs and 137 Cs were leached from the organic layer, and most of these (59-73%) were accumulated in the upper soil layer (0-5 cm). The proportion of 137 Cs (or 134 Cs) leaching from the organic layer was greater at sites receiving greater amounts of precipitation. The substantial accumulation of 137 Cs in the upper soil layer, irrespective of the 137 Cs deposition level or clay mineral composition, suggests that sorption capacities of clays and organic matter are sufficiently high to retain 137 Cs in the surface soil during at least the initial stage of contamination.

Radiocesium transfer from hillslopes to the Pacific Ocean after the Fukushima Nuclear Power Plant accident: A review

“…Takahashi et al (2015) found that the proportion of radiocesium in leaf litter, relative to soil, decreased from~90% in 2011 to 18e14% in 2012. Fujii et al (2014) also noted a significant decrease in the percentage of radiocesium in the leaf litter, decreasing from between 44e65% in 2011 to 14e27% in 2012. The transfer of radiocesium from litter to soil is controlled by rainfall and litter decomposition.…”

“…The rainfall that occurred immediately after the accident fallout may have been a factor in the radiocesium depth migration in forest soils (Teramage et al, 2014b) along with rainfall volume in general (Fujii et al, 2014). Further, rainfall was listed as a potential factor for the depth migration in the beach sand samples (Satou et al, 2015).…”

Input and output budgets of radiocesium concerning the forest floor in the mountain forest of Fukushima released from the TEPCO's Fukushima Dai-ichi nuclear power plant accident

“…A smaller amount of particulate matter transported from the experimental plot indicates a shallower erosion depth in the plot. Base on the 137 Cs depth distribution and its temporal changes in the forest soil after the FDNPP accident (Fujii et al, 2014;Takahashi et al, 2015), the shallower erosion depth increased the 137 Cs activity of eroded soil particles, even two to three years after the accident. However, it is extremely difficult to explain the differences in the 137 Cs activities of the particulate matter based on the differences in particulate matter weight (Table 8), which were less than 1 mm when the weight was converted into the erosion depth, assuming a dry soil density of 1.0 g cm À3 .…”

Radionuclides Released from Nuclear Accidents: Distribution and Dynamics in Soil

“…The raw organic layer holds 52 % of the Fukushima-derived 137 Cs and 25 % of the pre-Fukushima 137 Cs at the time of the soil sampling. Fujii et al (2014) also investigated the role of the organic layer of soil collected in Fukushima Prefecture (Kawauchi, Ohtama, and Tadami Town) during AugustSeptember of 2011 and 2012. The vertical soil distribution of 134 Cs and 137 Cs suggested that most cesium was retained in the organic layer and upper mineral soil layer under different levels of deposition.…”