Effectiveness of immediate and delayed AFCF application in reducing radiocaesium transfer to ryegrass

Following encouraging results obtained with the surface application of ammonium-ferric-hexacyano-ferrate (AFCF) to reduce radiocaesium transfer to ryegrass grown on surface-contaminated sandy soil, its efficacy as a countermeasure was investigated when recently deposited or ‘aged’ radiocaesium was homogeneously mixed with the soil. It was demonstrated that surface application of AFCF (1 and 10 g m-2) on a sandy soil decreased the transfer factor (TF) of radiocaesium immediately after surface contamination by a factor of 2•3 and 17•1, respectively. Distributing the deposit homogeneously with the soil led to a decrease by a factor of 2•3. Surface application at rates of 1 and 10 g AFCF m-2 further reduced the radiocaesium TF by a factor of 1•2 and 1•8, respectively. In the absence of AFCF treatment, two-year ageing contributes to a radiocaesium transfer factor decrease of mixed radiocaesium from 1•32 to 0•56 Bq g-1 DW/Bq g-1 soil (factor 2•4). Surface application of AFCF in amounts of 1 and 10 g m-2 reduced the TF of the aged radiocaesium, mixed with the soil, by a factor of 1•9 and 3•5, respectively. The presence of ‘aged’ AFCF (10 g m-2), surface applied immediately after deposition and mixed with the radiocaesium in the soil two years after treatment, still resulted in an about five times lower transfer factor compared to the ‘aged’, untreated control. AFCF did under no circumstances negatively affect plant growth. The results obtained strengthen previous results, showing that AFCF is an effective, long-lasting and non-toxic countermeasure for radiocaesium uptake on agricultural sandy soil.