The inflow of uranium 234U and 238U from the Vistula River catchment area to the Baltic Sea

Uranium in groundwater - A synopsis based on a large hydrogeochemical data set

Most of the knowledge on the occurrence of Uranium (U) in groundwater comes from in-situ manipulation experiments in the field, computational modelling studies or from laboratory analyses where individual processes of U mobilization were studied in isolation. Because of Uranium's vital redox chemistry it interacts, often simultaneously, with many other element cycles (e.g., sulfur, carbon, iron, and manganese) making it difficult to predict U concentrations in natural environments. For the present study a large data set was analyzed to predict the occurrence of U in groundwater from basic hydrochemistry. The data set consists of more than 8000 chemical groundwater analyses (including Uranium concentrations) from more than 2000 sampling locations. A strong relation between U concentrations and electric conductivity as well as alkalinity was observed, suggesting that weathering of geogenic source material and desorption from mineral surfaces is the principle mechanism of U release. Except for aquifers with strongly reducing conditions this process leads to a slow but continuous accumulation of U in groundwater in most cases. Importantly, the occurrence of U is modulated by the prevailing redox conditions in an aquifer. Uranium concentrations were moderate under oxic conditions and highest under manganese and nitrate-reducing conditions (heterotrophic as wells as autotrophic nitrate reduction). Only in iron- and sulfate-reducing groundwater the probability of U concentrations above 1 μg l^-1 was virtually zero, as these ground waters act as U sinks. The combination of mineral weathering (especially carbonates) with mobilization of U under manganese and nitrate reducing conditions results in the highest risk of detecting U. In contrast, a low risk is associated with low pH (<7) and low mineralization of groundwater, which is the case in granitic catchments, for example. Our results further provide evidence, that agricultural practices such as liming, use of fertilizers and irrigation influence the occurrence of U in groundwater in multiple ways. Accurate management of aquifers underlying farmland will therefore become more and more important in the future. In summary, we find that the vulnerability of an aquifer to elevated U concentrations cannot be explained by a single factor. This complicates efforts to target elevated U concentrations in groundwaters that are abstracted for drinking water production.

The radiological impact of phosphogypsum stockpile in Wiślinka (northern Poland) on the Martwa Wisła river water

The aim of this work was to determine the concentrations of uranium (234U, 235U, 238U), polonium (210Po) and lead (210Pb) radioisotopes in water samples and to explore the impact of the phosphogypsum stack on the Martwa Wisła waters. The 238U, 210Po and 210Pb concentrations in analyzed water samples reached maximum values of 11.7 ± 0.3, 2.0 ± 0.1 and 3.2 ± 0.1 mBq L-1 and activity ratios were maximally 1.18 ± 0.01 for 234U/238U, 0.041 ± 0.018 for 235U/238U and 0.69 ± 0.10 for 210Po/210Pb. The obtained results suggest that this impact is rather insignificant and does not affect significantly the Martwa Wisła river.

Activity disequilibrium between 234U and 238U isotopes in natural environment

The aim of this work was to calculate the values of the 234U/238U activity ratio in natural environment (water, sediments, Baltic organisms and marine birds from various regions of the southern Baltic Sea; river waters (the Vistula and the Oder River); plants and soils collected near phosphogypsum waste heap in Wiślinka (Northern Poland) and deer-like animals from Northern Poland. On the basis of the studies it was found that the most important processes of uranium geochemical migration in the southern Baltic Sea ecosystem are the sedimentation of suspended material and the vertical diffusion from the sediments into the bottom water. Considerable values of the 234U/238U are characterized for the Vistula and Oder Rivers and its tributaries. The values of the 234U/238U activity ratio in different tissues and organs of the Baltic organisms, sea birds and wild deer are varied. Such a large variation value of obtained activity ratios indicates different behavior of uranium isotopes in the tissues and organisms of sea birds and wild animals. This value shows that uranium isotopes can be disposed at a slower or faster rate. The values of the 234U/238U activity ratio in the analyzed plants, soils and mosses collected in the vicinity of phosphogypsum dumps in Wiślinka are close to one and indicate the phosphogypsum origin of the analyzed nuclides. Uranium isotopes 234U and 238U are not present in radioactive equilibrium in the aquatic environment, which indicates that their activities are not equal. The inverse relationship is observed in the terrestrial environment, where the value of the of the 234U/238U activity ratio really oscillates around unity.

Concentrations and fluxes of dissolved uranium in the Yellow River estuary: seasonal variation and anthropogenic (Water-Sediment Regulation Scheme) impact

The Water-Sediment Regulation Scheme (WSRS) of the Yellow River is a procedure implemented annually from June to July to expel sediments deposited in Xiaolangdi and other large middle-reach reservoirs and to scour the lower reaches of the river, by controlling water and sediment discharges. Dissolved uranium isotopes were measured in river waters collected monthly as well as daily during the 2010 WSRS (June 19-July 16) from Station Lijin (a hydrologic station nearest to the Yellow River estuary). The monthly samples showed dissolved uranium concentrations of 3.85-7.57 μg l(-1) and (234)U/(238)U activity ratios of 1.24-1.53. The concentrations were much higher than those reported for other global major rivers, and showed seasonal variability. Laboratory simulation experiments showed significant uranium release from bottom and suspended sediment. The uranium concentrations and activity ratios differed during the two stages of the WSRS, which may reflect desorption/dissolution of uranium from suspended river sediments of different origins. An annual flux of dissolved uranium of 1.04 × 10(8) g y(-1) was estimated based on the monthly average water discharge and dissolved uranium concentration in the lower reaches of the Yellow River. The amount of dissolved uranium (2.65 × 10(7) g) transported from the Yellow River to the sea during the WSRS constituted about 1/4 of the annual flux.

Polonium (²¹⁰Po), uranium (²³⁴U, ²³⁸U) isotopes and trace metals in mosses from Sobieszewo Island, northern Poland

The activity of polonium (210)Po and uranium (234)U, (238)U radionuclides, as well as trace metals in mosses, collected from Sobieszewo Island area (northern Poland), were determined using the alpha spectrometry, AAS (atomic absorption spectrometry) and OES-ICP (atomic emission spectrometry with inductively coupled plasma). The concentrations of mercury (directly from the solid sample) were determined by the cold vapor technique of CV AAS. The obtained results revealed that the concentrations of (210)Po, (234)U, and (238)U in the two analyzed kinds of mosses: schrebers big red stem moss (Pleurozium schreberi) and broom moss (Dicranum scoparium) were similar. The higher polonium concentrations were found in broom moss (Dicranum scoparium), but uranium concentrations were relatively low for both species of analyzed mosses. Among the analyzed trace metals the highest concentration in mosses was recorded for iron, while the lowest for nickel, cadmium and mercury. The obtained studies showed that the sources of polonium and uranium isotopes, as well as trace metals in analyzed mosses are air city contaminations transported from Gdańsk and from existing in the vicinity the phosphogypsum waste heap in Wiślinka (near Gdańsk).

Polonium, uranium and plutonium radionuclides in aquatic and land ecosystem of Poland

This article presents the results of study about distribution, inflow and accumulation of polonium, uranium and plutonium in aquatic and land environment of Poland and the southern Baltic Sea. Radionuclides of (210)Po, (234)U and (238)U as well as (239+240)Pu and (241)Pu are strongly accumulated in Baltic organisms and plants and transferred through the trophic chain. The values of bioconcentration factor (BCF) in Baltic plants and animals are higher for polonium and plutonium in comparison with uranium. The principal source of radionuclides in the southern Baltic Sea is their inflow with rivers. Total annual runoff of polonium, uranium and plutonium from the Vistula and the Odra as well as the Pomeranian rivers were calculated at 95 GBq of (210)Po, 750 GBq of (234+238)U and 160 MBq of (238+239+240)Pu. Seasonal and spatial variability of (210)Po, (238)U and (239+240)Pu levels in the Vistula and the Odra drainage basins were assessed by application of neural-network based classification, especially cluster analysis (CA), principal component analysis (PCA) and self-organizing maps (SOM). The result for the Vistula river indicated correlation between polonium and plutonium as well as polonium and uranium. In the Odra drainage basin, the biggest differences were observed in the case of (238)U. To assess if there are statistically significant differences in mean concentration values of (210)Po, (238)U and (239+240)Pu for the Vistula and the Odra rivers drainage basins were obtained by used of the non-parametric tests. Comparing to the Vistula catchment area, statistically differences concentration of (210)Po and (239+240)Pu in all year was observed for river samples collected on the Odra drainage basin.

The radiochemical contamination (²¹⁰Po and ²³⁸U) of zone around phosphogypsum waste heap in Wiślinka (northern Poland)

The aim of this work was the determination of the impact of phosphogypsum waste heap in Wiślinka (northern Poland) for radiological protection of zone around waste heap. These studies are very important for the estimation of natural alpha radionuclides contents in the vicinity of phosphogypsum waste heap and for environmental pollution assessment of this area. The process of bioaccumulation of radionuclides in interior plants parts prove to examine their origin sources, too. The activity of (210)Po, (234)U, and (238)U were measured using an alpha spectrometer. The values of uranium and polonium concentration in water with immediate area of waste heap are considerably higher than in the waters of the Martwa Wisła river. The values of activity ratio (234)U/(238)U are approximately about one in the phosphogypsum (0.97 ± 0.05) and in the water of retention reservoir and pumping station (0.92 ± 0.01 and 0.99 ± 0.08), while in the water from the Martwa Wisła river they are slightly higher than one (1.03 ± 0.07 and 1.17 ± 0.06). In the analyzed plants species the highest amounts of polonium and uranium were found in ruderal plants samples (between 51 ± 1 and 89 ± 1 for (210)Po; between 36 ± 3 and 68 ± 3 for (238)U) as well as hygrophilous plant samples (18 ± 1 and 84 ± 3; 42 ± 2 and 130 ± 4, respectively for (210)Po and (238)U). The more amounts of (210)Po and (238)U radionuclides were accumulated mainly in the roots of plant species in comparison to green parts. The general conclusion of realized study is higher influence of phosphogypsum on radioactive contamination of environmental zone around heap waste in Wiślinka (northern Poland).