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.

Radioecological investigation of 3H, 14C, and 129I in natural waters from Fuhrberger Feld catchment, Northern Germany.

Ongoing radionuclide releases from nuclear facilities, e.g. from reprocessing plants, but also from nuclear reactors require monitoring of the environment. Particularly drinking water reservoirs are prone to possible radionuclide accumulation fostering the need for routine surveillance. In this work, we investigated tritium (3H), radiocarbon (14C), and iodine-129 (129I) activity levels in natural aquatic samples at the water protection area of Fuhrberger Feld near Hannover city, Northern Germany. For that aim, a low-level liquid scintillation counting (LSC) technique was used to measure 3H in the water samples based on a distillation process after alkaline permanganate treatment. Isotopic ratios for both 14C and 129I were measured by accelerator mass spectrometry (AMS) after chemical separation and purification of the samples. Mean 3H levels in precipitation (8.8 ± 3.4 TU) were found to be comparable to its levels in precipitation data in Germany. Rivers and small streams revealed similar mean 3H value (11.0 ± 3.3 TU) as in lake water (10.6 ± 3.4 TU). Variations in 3H concentrations in groundwater samples were observed and discussed. 14C levels in all groundwater samples were below the atmospheric natural level of 100 pMC indicating no anthropogenic input of radiocarbon. The 129I/127I isotopic ratios in all investigated water samples were in the order of 10-8 to 10-7, which is significantly higher than the pre-nuclear natural equilibrium isotopic ratio (∼1.5 × 10-12). In strong contrast to all other regional groundwaters, the Fuhrberger Feld groundwater has much higher values of 129I concentration and 129I/127I isotopic ratio close to the ones of surface water. The overall annual effective dose via ingestion for all nuclides in the investigated groundwater remains substantially below the reference dose level of 0.1 mSv a-1.

Plutonium release from Fukushima Daiichi fosters the need for more detailed investigations.

The contamination of Japan after the Fukushima accident has been investigated mainly for volatile fission products, but only sparsely for actinides such as plutonium. Only small releases of actinides were estimated in Fukushima. Plutonium is still omnipresent in the environment from previous atmospheric nuclear weapons tests. We investigated soil and plants sampled at different hot spots in Japan, searching for reactor-borne plutonium using its isotopic ratio ²4°Pu/²³9Pu. By using accelerator mass spectrometry, we clearly demonstrated the release of Pu from the Fukushima Daiichi power plant: While most samples contained only the radionuclide signature of fallout plutonium, there is at least one vegetation sample whose isotope ratio (0.381 ± 0.046) evidences that the Pu originates from a nuclear reactor (²³9⁺²4°Pu activity concentration 0.49 Bq/kg). Plutonium content and isotope ratios differ considerably even for very close sampling locations, e.g. the soil and the plants growing on it. This strong localization indicates a particulate Pu release, which is of high radiological risk if incorporated.