Dynamics of ¹³⁷Cs Aggregated Transfer Factors to Animal Fodder: 35 Years after the Chernobyl Accident

The results of the analysis of the ¹³⁷Cs aggregated transfer factors (T_ag) change in fodder of agricultural animals (hay, haylage, silage, and green fodder) in the southwestern districts of Bryansk region over the 35 years since the Chernobyl accident are presented. It is shown that the rates of T_ag reduction across districts and zones of radioactive contamination varied significantly, while the dynamics of their change had an uneven character. Four time intervals are distinguished for the assessments; specifically, from 1987 to 1992, from 1993 to 2006, from 2007 to 2015, and from 2016 to 2021. The first period covered the time after the accident, when the countermeasures were carried out on a maximum scale; the second one, when the scales of remediation decreased significantly; the third period was a time (from 2006 to 2016) when the dynamics of the T_ag reduction was influenced by the Federal Target Program (FTP) “Preservation and Restoration of Soil Fertility of Agricultural Lands and Agricultural Landscapes as a National Asset of Russia for 2006–2013”; and the fourth one, from 2016 to 2021, in the remote period after the accident, when the volumes of rehabilitation of agricultural lands were very low. The half-lives calculated for the period of intensive countermeasure implementation ranged from 0.73 to two years. During the next period, the ¹³⁷Cs decrease in all types of forage crops strongly slowed down, and in many areas, there was a tendency toward an increase in the T_ag values. During the third and fourth periods, the dynamics was of multidirectional character; namely, in the districts where the FTP activities were applied on a full scale, an essential increase in the ¹³⁷Cs T_ag values to fodder plants was noted; whereas a further increase in this parameter was observed in the districts with limited application of the countermeasures. The efficiency of remediation was estimated by the criterion of reduction of T_ag values (reduction factor) in zones with different ¹³⁷Cs deposition density on agricultural lands. It was also noted that the reduction factor across different time intervals after the accident ranged from 1.1 (silage) to 5.1 (haylage). The highest efficiency in fodder crops T_ag reduction was observed both in the first period after the accident (1986–1992) and in the period of the FTP implementation. It was shown that the T_ag values in the zone with a deposition density from 185 to 555 kBq/m² did not differ significantly from those in the zone with a deposition density of 555–1480 kBq/m².