Preparation of Graphene Oxide-Maghemite-Chitosan Composites for the Adsorption of Europium Ions from Aqueous Solutions.

The adsorption of Eu(III) on composites synthesised from graphene oxide (GO), maghemite (MGH), and chitosan (CS) has been studied using different approaches. The physicochemical and morphological characteristics of the composites GO-MGH, GO-CS, GO-MGH-CS I, II, and III were determined by XRD, Mössbauer spectroscopy, FTIR, Raman spectroscopy, and TEM. According to the results of batch experiments, the maximum experimental adsorption capacity was 52, 54, 25, 103, and 102 mg/g for GO-MGH, GO-CS, GO-MGH-CS I, II, and III, respectively. The data obtained are in better agreement with the Langmuir, pseudo-second-order, and pseudo-first-order models only for GO-MGH. Thus, the adsorption of Eu(III) on the composites was a favourable, monolayer, and occurred at homogeneous sites. The nature of adsorption is chemical and, in the case of GO-MGH, physical. Tests of the composites in natural waters showed a high removal efficiency for Eu(III), Pu(IV), and Am(III), ranging from 74 to 100%. The ANFIS model has quite good predictive ability, as shown by the values for R2, MSE, SSE, and ARE. The GO-MGH-CS composites with the high adsorption capacity could be promising candidates for the removal of Eu(III) and the pre-concentration of Pu(IV) and Am(III) from natural waters.

Initiation of radioecological monitoring of forest soils and plants at the Lithuanian border region before the start of the Belarusian nuclear power plant operation.

Knowledge of the background activity concentrations of anthropogenic radionuclides before the start of operation of the new nuclear power plant in Belarus, BelNPP, is an issue of great importance for neighbouring countries. In this study, we provide the pilot characterisation of the Lithuanian part of the 30-km zone of the BelNPP, emphasising the forest plants, terrestrial mosses, forest organic and mineral topsoil to describe the preoperational radioecological state of the pine forest ecosystem. Key anthropogenic radionuclides (14C, 3H, 137Cs and 239,240Pu) were analysed. The 14C specific activity varied from 97.80 ± 1.30 to 102.40 ± 0.79 pMC. The 3H specific activity in the tissue-free water tritium form varied from 13.2 ± 2.2 TU to 20.8 ± 2.3 TU, which corresponded to the 3H level of precipitation in this region. The activity concentrations of 239,240Pu in soil and moss samples did not exceed 1 Bq/kg and were mainly due to global fallout after nuclear tests. The 137Cs inventory in the pine forest soils of the Lithuanian part of the BelNPP 30-km zone varied from 930 ± 70 to 1650 ± 430 Bq/m2. High variation of the inventory and uneven distribution in the soil profile conditioned a wide range of 137Сs activity in terrestrial plants from 1.0 ± 0.5 to 40.5 ± 1.8 Bq/kg dry weight. The abundance of microorganisms in different seasons and soil depths do not exceed the natural levels. According to PCA loads, the number of microorganisms and variability of 137Cs specific activity is determined by soil abiotic parameters.

What cooling pond sediments can reveal about 14C in nuclear power plant liquid effluents: Case study Lake Druksiai, Ignalina nuclear power plant cooling pond.

The vertical distribution of radiocarbon (14C) was examined in two bottom sediment cores, taken from Lake Druksiai which had been used as a cooling pond for the Ignalina nuclear power plant (INPP) with two RBMK type reactors. The aim of this work was to reconstruct 14C amounts in the lake ecosystem during an 8-year period after the INPP was closed, as any official monitoring of 14C in liquid releases from the INPP was not performed. The possibility of comparing the variation of the 14C specific activity in the corresponding layers of the same period of 3 different cores (one taken in 2013 and two in 2019) revealed the variability of the determined values of liquid radiocarbon discharges from the INPP into the lake. Cores taken in 2019 showed a permament14C release rate of 0.76±0.06 GBq/y all eight years after the closure of the INPP. The 14C release rate established from radiocarbon measurements in both cores did not differ by more than 0.8 GBq/y. However, including data from the core taken several years ago, the estimated radiocarbon release rate values varied within 1.3 GBq/y.

Blooms of Toxic Cyanobacterium Nodularia spumigena in Norwegian Fjords During Holocene Warm Periods.

In paleoecological studies, molecular markers are being used increasingly often to reconstruct community structures, environmental conditions and ecosystem changes. In this work, nodularin, anabaenopeptins and selected DNA sequences were applied as Nodularia spumigena markers to reconstruct the history of the cyanobacterium in the Norwegian fjords. For the purpose of this study, three sediment cores collected in Oslofjorden, Trondheimsfjorden and Balsfjorden were analyzed. The lack of nodularin in most recent sediments is consistent with the fact that only one report on the sporadic occurrence and low amounts of the cyanobacterium in Norwegian Fjords in 1976 has been published. However, analyses of species-specific chemical markers in deep sediments showed that thousands of years ago, N. spumigena constituted an important component of the phytoplankton community. The content of the markers in the cores indicated that the biomass of the cyanobacterium increased during the warmer Holocene periods. The analyses of genetic markers were less conclusive; they showed the occurrence of microcystin/nodularin producing cyanobacteria of Nostocales order, but they did not allow for the identification of the organisms at a species level.

Baltic Sea water tritium and stable isotopes in 2016-2017.

Water samples from the different basins of the Baltic Sea and North Sea were collected during four cruises taken place in 2016-2017. Altogether 60 water samples for 3H activity concentration and 120 water samples for stable isotopes ratio (δ18O and δ2H) were analysed. Exceptionally strong inflow activity from North Sea to the Baltic Sea occurred prior our surveys. The data obtained enabled comprehensive evaluation of tritium and stable isotopes distribution in waters of Baltic Sea and contributing inputs, including riverine and atmospheric freshwater flux and saline water inflow through the Danish Straits. By comparing with the previous studies, we noticed a tendency toward an increase in the δ18O and δ2H values of zero-salinity component over time, which may be due to climate change. In the case of tritium, the influence of artificial sources has also been noticed.

Distribution of radiocarbon in sediments of the cooling pond of RBMK type Ignalina Nuclear Power Plant in Lithuania.

The vertical distribution of radiocarbon (14C) was examined in the bottom sediment core, taken from Lake Druksiai, which has served as a cooling pond since 1983 for the 26 years of the Ignalina Nuclear Power Plant (INPP) operation using two RBMK-1500 reactors (Russian acronym for"Channelized Large Power Reactor"). 14C specific activity was measured in alkali-soluble and -insoluble fractions of the sediment layers. Complementary measurements of the 210Pb and 137Cs activity of the samples provided the possibility to evaluate the date of every layer formation, covering the 1947-2013 period. In addition, 14C distribution was examined in the scales of pelagic fish caught between 1980 and 2012. Our measurements reveal that, during the period 1947-1999, the radiocarbon specific activity in both fractions exhibits a parallel course with a difference of 5 ± 1 pMC (percent of modern carbon) being higher in alkali-soluble fraction, although 14C specific activity in both fractions increased by 11.4-13.6 pMC during the first 15 years of plant operation. However, during the 2000-2009 period, other than previously seen, a dissolved inorganic carbon (DIC) → aquatic primary producers → sediments 14C incorporation pattern occurred, as the radiocarbon specific activity difference between alkali-soluble and -insoluble fractions reached 94, 25, and 20 pMC in 2000, 2006, and 2008, respectively. Measurements in different sediment fractions allowed us to identify the unexpected organic nature of 14C contained in liquid effluences from the INPP in 2000-2009. The discrepancy between 14C specific activity in fish scales samples and DIC after 2000 also confirmed the possibility of organic 14C contamination. Possible reasons for this phenomenon might be industrial processes introduced at the INPP, such as the start of operation of the cementation facility for spent ion exchange resins, decontamination procedures, and various maintenance activities of reactor aging systems and equipment.

Carbon-14 in tree rings and other terrestrial samples in the vicinity of Ignalina Nuclear Power Plant, Lithuania.

The results of (14)C measurements in the annual tree rings from the Ignalina Nuclear Power Plant (INPP) surroundings, Lithuania, for the period of its operation from 1984 to 2002 are presented. The terrestrial samples, mainly moss and related soil, are studied in places as well. The tree rings have shown slightly enhanced (14)C activity due to operation of the nuclear power plant. The maximal calculated normalized (14)C release of 11TBqGW(e)(-1)year(-1) and the maximal effective dose of 2.0x10(-3)mSvyear(-1) resulting from the (14)C were estimated for 1999. For other years of INPP operation these values are lower. The excess of (14)C specific activity measured in the moss and soil samples from moss-covered sites near the nuclear power plant (up to 0.5km) showed highly elevated (14)C contents (up to 813pMC), probably indicating releases of particulate material.

The distribution of tritium in aquatic environments, Lithuania.

The aim of this study is to investigate mobile radionuclide tritium (3H or T) activity dynamics in aquatic environments related to Ignalina NPP (INPP) site and water bodies located in remote areas unaffected by the INPP. The 3H excess in the INPP environment was analyzed and compared to the variable 3H background level over the period of operation of the INPP (end of 1983 - end of 2009) and during the initial stage of decommissioning (2010-2017). 3H in the INPP vicinity has been studied in the water of artificial channels related to operation of the INPP and site drainage, in natural surface water bodies and, at a smaller scale, in unconfined groundwater. This study presents an extensive 3H data set extending back to 1980, i.e. before INPP operation started. To assess the contribution of global sources to 3H dynamics, monthly precipitation was also studied, along with water from the Baltic Sea, Curonian Lagoon and Nemunas River were studied as well, all three of these located in the Lithuanian maritime zone. The 3H activity concentration in water was measured using liquid scintillation counting (LSC) techniques (direct counting and counting after enrichment). During the period of INPP operation, 3H from liquid effluent could be clearly observed in discharge channels, occurring in rather low diluted conditions, as well as in Lake Druksiai, the cooling basin, at an even more diluted level. The highest 3H activity concentration in Lake Druksiai was observed in 2003 and reached 201.3 ± 1.3 TU at a time when 3H activity concentrations in background water bodies was 9.2 ± 3.5 TU. After the closure of the INPP, the 3H liquid effluent rate reduced by approximately two orders of magnitude (from 1012 Bq in 1991 to 1010 Bq in 2016) and when decommissioning activity commenced then the 3H activity concentration fell to that approaching the background level (19-27 TU) that can still be observed in industrial discharge and rainwater drainage channels. 3H as a result of leakage from the INPP can be observed in groundwater only in direct proximity to the INPP site near the radioactive waste storage zone.

Investigations of the unsaturated zone at two radioactive waste disposal sites in Lithuania.

The unsaturated zone is an important part of the water cycle, governed by many hydrological and hydrogeological factors and processes and provide water and nutrients to the terrestrial ecosystem. Besides, the soils of the unsaturated zone are regarded as the first natural barrier to a large extent and are able to limit the spread of contaminants depending on their properties. The unsaturated zone provides a linkage between atmospheric moisture, groundwater, and seepage of groundwater to streams, lakes, or other surface water bodies. The major difference between water flow in saturated and unsaturated soils is that the hydraulic conductivity, which is conventionally assumed to be a constant in saturated soils, is a function of the degree of saturation or matrix suction in the unsaturated soils. In Lithuania, low and intermediate level radioactive wastes generated from medicine, industry and research were accumulated at the Maisiagala radioactive waste repository. Short-lived low and intermediate levels radioactive waste, generated during the operation of the Ignalina Nuclear Power Plant (INPP) and arising after the INPP decommissioning will be disposed of in the near surface repository close to the INPP (Stabatiske site). Extensive data sets of the hydraulic properties and water content attributed to unsaturated zone soil profiles of the two radioactive waste disposal sites have been collected and summarized. Globally widespread radionuclide tritium ((3)H) and stable isotope ratio ((18)O/(16)O and (2)H/(1)H) distribution features were determined in precipitation, unsaturated zone soil moisture profiles and groundwater.