Freshwater bodies with high radioactivity are often contaminated with chemicals, including heavy metals. Of particular interest is cadmium, which is toxic to living organisms. The article considers the effects on different levels of biological organization in duckweed Lemna minor L. when exposed to acute γ-radiation and cadmium ions (Cd). The plants were irradiated at doses of 11 and 63 Gy, and then cultured for 7 days on a medium with 0.315 and 12.6 µmol/L Cd, which corresponded to the minimum effective and half-maximum (50%) intensities of the impact of these factors on the specific growth rate of the laboratory duckweed culture. The effect of interaction of factors was calculated using median effect analysis. The growth rate under joint action was lower in most cases compared to the separate action of only radiation or Cd. Growth rate inhibition at 63 Gy and 12.6 µmol/L Cd increased to 65%. Analysis of the effects at the population level showed that at low radiation doses the factors interacted as antagonists, and at high doses as synergists. Under the influence of stressors the average size of fronds (green plates) decreased: by 35% at 12.6 µmol/L Cd, by 15% under γ-radiation (63 Gy), and by 41% under combined action compared to untreated plants. Under combined action of the factors the degree of damage to the frond surface in the form of chlorosis and/or necrosis increased, including up to 100% at 63 Gy and 12.6 µmol/L Cd. The degree of frond damage is associated with a decrease in chlorophyll a content (r = −0.76, p 0.05) and an increase in malondialdehyde concentration (r = 0.91, p 0.05). At 12.6 µmol/L Cd in the medium, the chlorophyll content decreased by half compared to unexposed plants. In contrast, high doses of radiation contributed to an increase in the content of chlorophylls and carotenoids (p 0.05). After 11 and 63 Gy, Cd accumulation in the tissues of irradiated plants increased by 1.8 and 3.2 times compared to unexposed plants at 0.315 µmol/L Cd in the medium (p 0.05). This study confirmed the importance of risk assessment for radioactive contamination of water bodies, taking into account the toxicity of associated stressors.
Bodnar et al. (Wed,) studied this question.