Transfer of 137Cs to agricultural products in southern Sweden after a nuclear accident

This report contains calculations of expected 137Cs transfer from contaminated agricultural land to crop and animal products in the southern part of Sweden; Skaane and Blekinge. The fallout has been simulated to be 1 MBq per m2, uniformly deposited on the ground surface in the spring of 1995. The report covers a period of 20 years or the years 1996-2015. The calculations of 137Cs transfer to crop products are based on official crop statistics of the year 1996 and earlier observed soil/plant transfer ratios. These ratios vary with crop and soil type. The sensitivity for 137Cs-transfer from soil to plant varies between the counties. This variability depends on smaller root uptake in loamy than in sandy soils and less in sandy than in organic soils, and to a different distribution of these three soil types. The 137Cs-transfer to crop products decreases considerably during a 20 years period. This depends on nuclide decay and on decreased root availability. As shown in tables and figures, the decrease is larger during the first years after fallout than later. This depends on successive ploughing of grass land during the crop rotation, which drastically decreases the root availability. Agricultural land is used for cultivating sale and fodder crops. The fodder crops are the main bases for transfer to animal products. The passage through the animal body will cause the main part of the 137Cs intake to be linked off before the transfer to the animal products. The 137Cs-content in a certain product will finally determine if it can be used for human intake. The 137Cs-transfer to cow feed in MBq per 100 hectare decreases with time and, in analogy with the mean transfer to all crop products, more in the first years than in later years due to successive ploughing of grassland in the existing crop rotations. The calculations for the counties, which were made against the background of earlier Swedish micro plot and field experiments, clearly show that it will be effective to reduce the 137Cs transfer to crop products by different countermeasures. As regards soil types, it can be necessary to delete the use of organic soils. As regards crops, it can be necessary to change the crop rotation. The two most important countermeasures, which immediately can be made by farmers to reduce the 137Cs transfer to crop products, are extra potassium fertilisation and ploughing before reuse of contaminated land. As shown by the calculations for the counties, extra potassium fertilisation may on an average be expected to decrease the 137Cs content of cow milk by a factor of 3. As described in section 2 the soil and the conditions for crop growth vary between and within the counties and thereby also the sensitivity for root uptake of 137Cs. Implementation of the results on a certain farm must therefore be adjusted to the site specific situation and type of husbandry. This was the main reason for the case study of transfer on four model farms and also for a more detailed discussion of countermeasures to reduce the 137Cs transfer to different plant and animal products. The simultaneous deposition of 134Cs, which at the Chernobyl accident half-time for 134Cs is only 2.1 years compared to 30 years for 137Cs it will also contribute to the contamination of agricultural products for at least a decade, and especially in grass from unploughed pasture land