Weathering half-life of radioactive cesium for winter rye (Secale cerealeL.) and Italian ryegrass (Lolium multiflorumLam.) directly contaminated by the 2011 Fukushima Daiichi Nuclear Power Station accident

Abstract

Changes in radioactive cesium (radiocesium) concentrations in winter rye (Secale cereale L.) and Italian ryegrass (Lolium multiflorum Lam.) grown in fields contaminated by the accident at the Fukushima Daiichi Nuclear Power Station of the Tokyo Electric Power Company were examined to clarify the half-lives of weathering as an environmental process that removed radiocesium during the early stages after its deposition. The radiocesium concentrations in the rye plants that resulted from direct deposition of fallout in 2011 decreased greatly from 140.5 kBq kg -1 dry weight (DW) on March 31 to 13.2 kBq kg -1 DW on April 27, during the 27 d between the vegetative growth and heading stages. The amounts of rye radiocesium per unit area decreased simultaneously, from 69.8 kBq m -2 to 12.6 kBq m -2. The radiocesium concentrations in rye were half and a quarter of those in Italian ryegrass during the vegetative and heading stages, respectively, although the radiocesium concentrations in Italian ryegrass also decreased with plant growth. The values of the weathering half-life of 8.0 and 11.0 d for the radiocesium concentration per unit DW and amount per unit area in rye were approximately half those of Italian ryegrass, at 14.1 and 23.1 d, respectively. Therefore, less radiocesium-contaminated material seemed to be retained on the plant surface of rye than on Italian ryegrass. The radiocesium concentrations of rye harvested in the same experimental fields in the year following the accident were below the value defined in the February 2012 provisional regulation for cattle roughage (100 Bq kg -1 at a water content of 0.8 kg kg -1).

Cesium-137 concentration of forage corn and Italian ryegrass in a double cropping system under different rates of cattle farmyard manure application after the Fukushima Daiichi Nuclear Power Station accident in 2011

“…We observed the interception of radioactive Cs on crop surfaces by direct deposition was rapidly decreased in the spring of 2011 in NILGS (Sunaga et al 2015). Based on the previous research, it appears that 18% of total deposition was observed in the Italian ryegrass harvest in 2011.…”

Four‐year decline in radioactive cesium transfer to perennial Gramineae candidate bioenergy crops in a field polluted by radioactive fallout from the Fukushima Daiichi Nuclear Power Plant in 2011

“…In the case of rye ( Secale cereale L.) sown in October 2011 in two plowed and rototilled fields at the NARO‐ILGS Nasu Research Station and harvested in May 2012, the combined radioactivity of the two isotopes in the foliage was 13.4 Bq kg −1 DM in a field that received cattle manure compost at 1.5 kg m −2 and 19.2 Bq kg −1 DM in a field that received the compost at 4.5 kg m −2 (Sunaga et al . ). Exchangeable K 2 O levels, which lowers cesium uptake, were 0.192 g kg −1 and 0.754 g kg −1 in the respective fields.…”

“…; Sunaga et al . ), our knowledge of such transfer in bioenergy crops is very limited. Production of perennial Gramineae bioenergy crops is characterized by long‐term and high‐yielding cultivation, a deep rhizosphere, labor‐saving management, and whole‐crop harvesting by relatively large machines.…”

Contamination of agricultural products and soils with radiocesium derived from the accident at TEPCO Fukushima Daiichi Nuclear Power Station: monitoring, case studies and countermeasures

“…Radiocesium concentration in herbaceous grass decreased much faster than predicted by physical decay of radiocesium. This may be due, in part, to the fact that some fractions of deposits were soluble and washed out by rain (Sunaga et al 2015). Compared with herbaceous grass from permanent grassland, annual forage crop was less contaminated.…”