Differentiation between chemo- and radiotoxicity of ¹³⁷Cs and ⁶⁰Co on Lemna minor

The uptake and effects of stable Cs and Co on L.minor were extensively studied, together with the effects of gamma radiation using a ¹³⁷Cs or ⁶⁰Co source. Innovative is that we combined external irradiation (from ¹³⁷Cs or ⁶⁰Co sources) with the direct uptake of certain amounts of stable Cs or Co to simulate the impact of the same mass of a radioisotope compared with that of the stable element. Such approach allows to differentiate between chemo- and radiotoxicity of ¹³⁷Cs or ⁶⁰Co, permitting to study the ¹³⁷Cs and ⁶⁰Co uptake by L. minor without using high concentrations of these elements in solution. Our results indicate that radiotoxicity of both ¹³⁷Cs and ⁶⁰Co has a greater importance compared to their chemotoxicity. This was also supported by the independent action and concentration addition concepts. Both concepts resulted in a good prediction of the dose-response curve of the combination exposure. The maximal removal of ¹³⁷Cs or ⁶⁰Co per gram dry matter of L. minor was lower compared with the removal of the corresponding stable isotope. The toxicity of ⁶⁰Co was higher compared to ¹³⁷Cs based on EC₅₀ values and uptake data. With respect to the effects on photosynthetic pigments, starch and soluble sugars contents, only starch increased in a concentration- and dose-dependent manner.