RADIOACTIVE CONTAMINATION BY CESIUM-137 OF FLOODPLAINS AND WATER OF THE TECHA AND ISET RIVERS

Abstract

The article presents an analysis of data from literature sources and actual data from Roshydromet on
radioactive contamination with ¹³⁷Cs of floodplain territories and waters of the Techa and Iset rivers, which are part of
the Ob-Irtysh basin. The consequences of radioactive waste discharges into the Techa River (1949–1951) and the accident
at the reservoir containing high-level liquid radioactive waste at the Mayak Production Association (PO Mayak) are examined in detail.
The analysis revealed significant differences in the distribution of radioactive ¹³⁷Cs between the rivers: there is a
decrease in the volumetric activity of ¹³⁷Cs downstream of the Techa River, while in the Iset River contamination levels
remain relatively stable in different sections. The sources of secondary contamination of the Techa River waters are
sections of the contaminated floodplain since, despite the decades that have passed (this period exceeding more than 2
half-lives of ¹³⁷Cs (T₁/₂ = 30.2 years)), contamination levels in some sections of the floodplain of the studied rivers remain
high.
It is noted that methodological approaches developed in geomorphology and landscape science were not widely
used when collecting and analyzing data on the accumulation, accretion, and distribution of radiocesium in the floodplain
landscapes. Firstly, there was insufficient attention to hydrological aspects: there was no detailed analysis of water and
sediment runoff, of the seasonal and long-term fluctuations. Secondly, when surveying the valleys of the Techa and Iset
rivers, many studies lacked precise topographic referencing of sampling locations due to the absence of a cartographic
base of appropriate quality and the low accuracy of GPS equipment at that time. Layer-by-layer sampling of floodplain
deposits was typically carried out with a large step of 5 cm. These shortcomings, associated with technical capabilities at
the time of mass studies in the Techa River floodplain, significantly limit the possibilities for correct interpretation of the
results of assessments of horizontal migration processes and redistribution of radionuclides at different distances from the
main contamination zones.