Forms of Soil Toxicity in Areas with a High Degree of Long-Term Radionuclide Contamination Identified by a Solid-Phase Biotest with Allium cepa

This article presents the results of measurement of the toxicity of soils with a specific activity of Cs137 in the range of 3.3 × 102 to 1.3 × 106 Bq/kg; the flux density of β-particles and dose rate of γ-radiation on the surface of a bulk sample were 5.4–192.7 imp/s/cm2 and 0.2–2.7 µSv/h, respectively. The forms of toxicity were detected in a solid-phase biotest with Allium cepa L., which simulated the situation of external irradiation of dividing cells in contact with soil. The toxic effect was assessed relative to the control as mitotoxicity by the decrease in the mitotic index and as genotoxicity based on the induction of chromosomal aberrations, taking into account the contribution of the clastogenic effect. The value of the mitotic index in a series of biotests with contaminated soil decreased to 8.6 ± 1.1–14.6 ± 2.3% compared to the control proliferation level of 14.9 ± 1.2%. At the same time, the frequency of chromosomal aberrations increased from 4.7 ± 0.3 to 18.2 ± 3.3% at a control level of 3.9 ± 0.5%, with an increase to 68% of the proportion of pathologies due to clastogenic effects on chromosomes. A number of significant correlations have been revealed between the values of toxicity indices and indicators of radioactive contamination of soils.