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.

Effects of environmental parameters on Lemna minor growth: An integrated experimental and modelling approach.

Pollution of surface waters is a worldwide problem for people and wildlife. Remediation and phytoremediation approaches can offer a solution to deal with specific scenarios. Lemna minor, commonly known as duckweed, can absorb and accumulate pollutants in its biomass. To evaluate if L. minor could be applied for phytoremediation purposes, it is necessary to further investigate its remediation capability and to identify which parameters affect the remediation process. Such a model must include both plant growth and pollutant exchange. A remediation model based on a robust experimental study can help to evaluate L. minor as a proper remediation strategy and to predict the outcome of a L. minor based remediation system. To set up this model, this paper focusses on a detailed experimental study and a comprehensive mathematical modelling approach to represent L. minor growth as a function of biomass, temperature, light irradiation and variable nutrient concentrations. The influence of environmental conditions on L. minor growth was studied, by composing 7 days growth curves. Plants were grown under predefined environmental conditions (25°C, 14h photoperiod, 220 µmol m-2 s-1 light intensity and a modified Hoagland solution with 23.94 mg N L-1 and 3.10 mg P L-1 (N:P ratio of 7.73)) as standard for all experiments. The influence of different temperatures (6, 10, 15, 20, 25, 30 and 35°C), light intensities (63, 118, 170, 220 and 262 µmol m-2 s-1), photoperiods (12h and 14h) and N:P ratios (1.18, 3.36, 7.73 and 29.57) were tested in the model. As a result, a growth model was optimised using separate datasets for temperature, light intensity, photoperiod and nutrients and validated by further integrated testing. The growth model is a stable platform for application in phytoremediation of radionuclides in contaminated water, to be extended in future studies with information of pollutant uptake, pollutant-nutrient interactions and transfer to the biomass.