Does low uranium concentration generates phytotoxic symptoms in Pisum sativum L. in nutrient medium?

Due to excessive mining and use of radionuclide especially uranium (U) and its fission products, numerous health hazards as well as environmental contamination worldwide have been created. The present study focused on demonstrating whether low concentration of U treatment in liquid nutient medium may translocate traces of U in plants and in fruits of Pisum sativum after 30 and 60 days of exposure for the safe use as a food supplement for human/animals. Hydroponically grown plants (in amended Hoagland medium) were treated with two different concentrations of uranium ([U] = 100 and 500 nM, respectively). Plants showed a decrease in total chlorophyll after 60 days of treatment. On the other hand, Eh of the nutrient medium was not affected from the initial days till 60 days of treatment, but pH of nutrient medium was increased upon durations, highest at 60 days of treatment. In seeds, micro/macro elements were under limit as well as U concentration was also under detection limit. We did not observe any U in the above ground parts (shoots/seeds) of the plant, i.e., under detection limit. Our observation suggests that P. sativum plants may be useful to grow at low radionuclide [U]-contaminated areas for safe human/animal use, but for other fission products, we have to investigate further for the safe human/animal use.

Uptake of Plutonium-238 into Solanum tuberosum L. (potato plants) in presence of complexing agent EDTA.

Bioavailability and plant uptake of radionuclides depend on various factors. Transfer into different plant parts depends on chemical and physical processes, which need to be known for realistic ingestion dose modelling when these plants are used for food. Within the scope of the present work, the plutonium uptake by potato plants (Solanum tuberosum L.) was investigated in hydroponic solution of low concentration [Pu] = 10-9 mol L-1. Particular attention was paid to the speciation of radionuclides in the solution which was modelled by the speciation code PHREEQC. The speciation, the solubility and therefore the plant availability of radionuclides mainly depend on the pH value and the redox potential of the solution. During the contamination period, the redox potential did not change significantly. In contrast, the pH value showed characteristic changes depending on exudates excreted by the plants. Plant roots took up high amounts of plutonium (37%-50% of the added total amount). In addition to the uptake into the roots, the radionuclides can also adsorb to the exterior root surface. The solution-to-plant transfer factor showed values between 0.03 and 0.80 (Bq kg-1/ Bq L-1) for the potato tubers. By addition of the complexing agent EDTA (10-4 mol L-1), the plutonium uptake from solution increased by 58% in tubers and by 155% in shoots/leaves. The results showed that excreted substances by plants affect bioavailability of radionuclides at low concentration, on the one hand. On the other hand, the uptake of plutonium by roots and the accumulation in different plant parts can lead to non-negligible ingestion doses, even at low concentration. We are aware of the limited transferability of data obtained in hydroponic solutions to plants growing in soil. However, the aim of this study is twofold: First we want to investigate the influence of Pu speciation on plant uptake in a rather well defined system which can be modelled using available thermodynamic data. Second, techniques developed here shall be applied to the investigation of plants growing in soil in the future. The present work contributes to the basic understanding how plant induced effects on nutrient solution influence bioavailability of radionuclides and fosters the need for more detailed investigations of the complex uptake and accumulation processes of radionuclides into plants.

Investigation of low-level 242Pu contamination on nutrition disturbance and oxidative stress in Solanum tuberosum L.

Plutonium associated with higher molecular weight molecules is presumed to be poorly mobile and hardly plant available. In our present study, we investigate the uptake and effects of Pu treatments on Solanum tuberosum plants in amended Hoagland medium at concentrations of [242Pu] = 100 and 500 nm, respectively. We found a direct proof of oxidative stress in the plants caused by these rather low concentrations. For the confirmation of oxidative stress, we explored the production of nitric oxide (NO) and hydrogen peroxide (H2O2) by epifluorescence microscopy. Oxidative stress markers like lipid peroxidation and superoxide radicals (O2•-) are monitored through histochemical analysis. The biochemical parameters i.e. chlorophyll and carotenoids are measured as an indicator of cellular damage in the tested plants including the enzymatic parameters such as catalase and glutathione reductase. From our work, we conclude that Pu in low concentration has no significant effects on the uptake of many trace and macroelements. In contrast, the content of O2•- , malondialdehyde (MDA), and H2O2 increases with increasing Pu concentration in the solution, while the opposite effects was found for NO, catalase, and glutathione reductase. These findings prove that even low concentration of Pu regulates ROS production and generate oxidative stress in S. tuberosum L.