An environmentally recovered, mixed Pu-U hot particle from the Thule accident, Greenland has been analyzed by Scanning Electron Microscopy and a large-geometry Secondary Ion Mass Spectrometry based Scanning Ion Imaging (SII) method for simultaneous U-235,U-236,U-238 and Pu-239,Pu-240 isotope compositions. This SII technique permits the visual assessment of the spatial distribution of the isotopes of U and Pu and can be used to obtain quantitative isotope ratios in any user-defined square region up to a few 100 itm in size. The particle measured here has two resolvable U isotopic compositions with a single composition of weapons grade Pu. The bulk of the particle has,, enriched U and weapons-grade Pu with U-235/U-238, U-236/U-238 and Pu-240/Pu-239 of 1.12 +/- 0.04, 0.006 +/- 0.002, 0.054 +/- 0.004, respectively (2 sigma). The Pu isotopic ratio was consistent across the Pu-239/U-238(raw) sample but decreased from 1.99 +/- 0.07 to 0.11 +/- 0.04 (2 sigma) corresponding to the area of the particle with a resolvably different U isotope composition. This portion of the particle has U-235/U-238 U-236/U-238 and Pu-240/Pu-239 ratios of 0.11 +/- 0.04, 0.001 +/- 0.002, and 0.05 +/- 0.04, respectively (2 sigma). The origin of the less enriched U could be environmental that mixed with the particle or heterogeneously enriched U from the weapons. The heterogeneity of hot particles on a micrometer scale highlights the need for spatially resolved techniques to avoid mixing during a bulk or whole particle analysis, as the mixing end members here would have been lost, and the measured ratios would have been inaccurate.

This work provides a novel data set on accumulations of both anthropogenic (Cs-137, Pu-238, Pu239+240, Am-241) and natural (Pb-210, Ra-226, Th-232) radionuclides and an element (K). Sampling of soils and lake sediments was accomplished in 1999 during Tundra Northwest (TNW-99) international expedition to a remote region of the Canadian Arctic. The sediment ages and sedimentation rates were determined. The obtained results overall indicated a high geographical diversity of contamination levels and trends. Accumulation rates were also differential, and a sediment focusing contribution was distinctly visible. Radioactive pollution was found to be lower relative to temperate counterparts. The activity ratios of anthropogenic radionuclides corresponded to global fallout as a prevailing source in the entire examined area. The post-Chernobyl radiocaesium was observed for the westernmost lake only. The elevated level of Cs-137 and Pu239+240 in the topmost sediment at the northern and eastern Arctic Archipelago was attributed to recent resuspension and subsequent redistribution of radionuclides.

To analyze plutonium (Pu) in open ocean waters can be challenging due to the low seawater concentrations. In this study we compared two techniques for Pu determination, one in-situ MnO2 cartridge system and the more commonly used MnO2 precipitation technique. During the pre-pilot GEOTRACES cruise ANT XXX-1 (2005) we tested MnO2 cartridges for the pre-concentration of Pu from seawater at 19 sampling stations on a transect in the southeastern Atlantic Ocean between Vigo (Spain) and Cape Town (South Africa). Our in-situ sampling setup consisted of one particle cartridge followed by three MnO2 cartridges in a series. Through the system we pumped between 956 and 2700 I of surface seawater with a flow rate between 1.6 and 5.21/min. We found that the adsorption efficiency of a single MnO2 cartridge to adsorb Pu was rather constant and on average a 58 +/- 7%. The adsorption efficiency was also found to be independent of seawater: temperature in the range of 18.3-29.2 degrees C, salinity range 34.2-37.1 parts per thousand, and conductivity in the range of 46.8-58.4 mS/cm. In parallel with the in-situ sampling, discrete surface water samples between 259 and 281 I were taken and Pu was pre-concentrated using the MnO2 precipitation method. We find a good agreement between the Pu concentrations determined with the two different techniques. The in-situ pre-concentration technique requires more radiochemical work in the laboratory but has the advantage that large seawater volumes can be sampled without the necessity for radiochemical processing on-board the ship. The much larger volumes sampled with the in-situ technique compared with the precipitation technique, enables accurate determination of Pu-isotopic ratios with a low relative standard deviation. We have shown in this study that in-situ MnO2 cartridge technique can be used in a reliable way for the determination of dissolved Pu seawater concentration in open ocean waters.

Laboratories from 14 countries (with different levels of expertise in radionuclide measurements and Pb-210 dating) participated in an interlaboratory comparison exercise (ILC) related to the application of Pb-210 sediment dating technique within the framework of the IAEA Coordinated Research Project. The laboratories were provided with samples from a composite sediment core and were required to provide massic activities of several radionuclides and an age versus depth model from the obtained results, using the most suitable Pb-210 dating model. Massic concentrations of Zn and Cu were also determined to be used for chronology validation. The ILC results indicated good analytical performances while the dating results didnt demonstrate the same degree of competence in part due to the different experience in dating of the participant laboratories. The ILC exercise enabled evaluation of the difficulties faced by laboratories implementing Pb-210 dating methods and identified some limitations in providing reliable chronologies.

Inhalation of uranium aerosols is a concern in nuclear fuel fabrication. Determination of committed effective doses and lung equivalent doses following inhalation intake requires knowledge about aerosol characteristics; e.g., the activity median aerodynamic diameter (AMAD). Cascade impactor sampling of uranium aerosols in the breathing zone of nuclear operators was carried out at a nuclear fuel fabrication plant producing uranium dioxide via ammonium uranyl carbonate. Complementary static sampling was carried out at key process steps. Uranium on impaction substrates was measured using gross alpha counting and alpha spectrometry. Activity size distributions were evaluated for both unimodal and bimodal distributions. When a unimodal distribution was assumed, the average AMAD in the operator breathing zone at the workshops was 12.9-19.3 mu m, which is larger than found in previous studies. Certain sampling occasions showed variable isotope ratios (U-234/U-238) at different impactor stages, indicating more than one population of particles; i.e., a multimodal activity size distribution. When a bimodal distribution (coarse and fine fraction) was assumed, 75-88% of the activity was associated with an AMAD of 15.2-18.9 mu m (coarse fraction). Quantification of the AMAD of the fine fraction was associated with large uncertainties. Values of 1.7-7.1 mu m were obtained. Static sampling at key process steps in the workshops showed AMADs of 4.9-17.2 mu m, generally lower than obtained by breathing zone sampling, when a unimodal distribution was assumed. When a bimodal distribution was assumed, a smaller fraction of the activity was associated with the coarse fraction compared to breathing zone sampling. This might be due to impactor positioning during sampling and sedimentation of large particles. The average committed effective dose coefficient for breathing zone sampling and a bimodal distribution was 1.6-2.6 mu Sv Bq(-1)for(234)U when Type M/S absorption parameters were assumed (5.0 mu Sv Bq(-1)for an AMAD of 5 mu m). The corresponding lung equivalent dose coefficient was 3.6-10.7 mu Sv Bq(-1)(29.9 mu Sv Bq(-1)for an AMAD of 5 mu m). The predicted urinary excretion level 100 d after inhalation intake was found to be 13-34% of that corresponding to an AMAD of 5 mu m. Uranium aerosols generated at a nuclear fuel fabrication plant using ammonium uranyl carbonate route of conversion were associated with larger AMADs compared to previous work, especially when sampling of aerosols was carried out in the operator breathing zone. A bimodal activity size distribution can be used in calculations of committed effective doses and lung equivalent doses, but parameters associated with the fine fraction must be interpreted with care due to large uncertainties.

Detailed aerosol knowledge is essential in numerous applications, including risk assessment in nuclear industry. Cascade impactor sampling of uranium aerosols in the breathing zone of nuclear operators was carried out at a nuclear fuel fabrication plant. Collected aerosols were evaluated using scanning electron microscopy and energy dispersive X-ray spectroscopy. Imaging revealed remarkable variations in aerosol morphology at the different workshops, and a presence of very large particles (up to ≅ 100 × 50 μm²) in the operator breathing zone. Characteristic X-ray analysis showed varying uranium weight percentages of aerosols and, frequently, traces of nitrogen, fluorine and iron. The analysis method, in combination with cascade impactor sampling, can be a powerful tool for characterization of aerosols. The uranium aerosol source term for risk assessment in nuclear fuel fabrication appears to be highly complex.

Inhalation exposure to uranium aerosols can be a concern in nuclear fuel fabrication. The ICRP provides default absorption parameters for various uranium compounds but also recommends determination of material-specific absorption parameters to improve dose calculations for individuals exposed to airborne radioactivity. Aerosol particle size influences internal dosimetry calculations in two potentially significant ways: the efficiency of particle deposition in the various regions of the respiratory tract is dependent on aerodynamic particle size, and the dissolution rate of deposited materials can vary according to particle size, shape, and porosity because smaller particles tend to have higher surface-to-volume ratios than larger particles. However, the ICRP model assumes that deposited particles of a given material dissolve at the same rate regardless of size and that uptake to blood of dissolved material normally occurs instantaneously in all parts of the lung (except the anterior portion of the nasal region, where zero absorption is assumed). In the present work, the effect of particle size on dissolution in simulated lung fluid was studied for uranium aerosols collected at the plant, and its influence on internal dosimetry calculations was evaluated. Size fractionated uranium aerosols were sampled at a nuclear fuel fabrication plant using portable cascade impactors. Absorption parameters, describing dissolution of material according to the ICRP Human Respiratory Tract Model, were determined in vitro for different size fractions using simulated lung fluid. Samples were collected at 16 time-points over a 100-d period. Uranium content of samples was determined using inductively coupled plasma mass spectrometry and alpha spectrometry. In addition, supplementary experiments to study the effect of pH drift and uranium adsorption on filter holders were conducted as they could potentially influence the derived absorption parameters. The undissolved fraction over time was observed to vary with impaction stage cut-point at the four main workshops at the plant. A larger fraction of the particle activity tended to dissolve for small cut-points, but exceptions were noted. Absorption parameters (rapid fraction, rapid rate, and slow rate), derived from the undissolved fraction over time, were generally in fair agreement with the ICRP default recommendations for uranium compounds. Differences in absorption parameters were noted across the four main workshops at the plant (i.e., where the aerosol characteristics are expected to vary). The pelletizing workshop was associated with the most insoluble material and the conversion workshop with the most soluble material. The correlation between derived lung absorption parameters and aerodynamic particle size (impactor stage cut-point) was weak. For example, the mean absorption parameters derived from impaction stages with low (taken to be <5 mu m) and large (>= 5 mu m) cut-points did not differ significantly. Drift of pH and adsorption on filter holders appeared to be of secondary importance, but it was found that particle leakage can occur. Undissolved fractions and to some degree derived lung absorption parameters were observed to vary depending on the aerodynamic size fraction studied, suggesting that size fractionation (e.g., using cascade impactors) is appropriate prior to conducting in vitro dissolution rate experiments. The 0.01-0.02 mu m and 1-2 mu m size ranges are of particular interest as they correspond to alveolar deposition maxima in the Human Respiratory Tract Model (HRTM). In the present work, however, the dependency on aerodynamic size appeared to be of minor importance, but it cannot be ruled out that particle bounce obscured the results for late impaction stages. In addition, it was noted that the time over which simulated lung fluid samples are collected (100 d in our case) influences the curve-fitting procedure used to determine the lung absorption parameters, in particular the slow rate that increased if fewer samples were considered.

The performance characteristics of the Agilent 8900 triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) system were evaluated and optimised concerning stability in measurements of uranium isotopic ratios. Multiple measurement parameters were evaluated for the determination of U isotopic ratios in certified standard solutions containing U-233, U-235 and U-238. Large irregular biases during repeated measurements of U isotopic ratios were observed using two identical ICP-MS/MS instruments. Depending on the mass filter resolution settings, the accuracy of U isotopic ratios can deviate up to 100% from the certified reference value. These variations in U isotopic ratios are primarily recognised as irregular drifts in the mass calibration of the two mass filters. This mass calibration drift is dependent on the isotope mass with a more pronounced drift for heavier isotopes. In order to solve the problem the resolution settings were optimised for both mass filters, which resulted in considerable improvement in precision and accuracy. A precision of 0.07% (relative standard deviation) for long-term measurement of U-233/U-235 ratios was achieved. Mass bias corrected U isotopic ratios agree very well with certified reference values with overall relative deviations from reference values of 0.005% and 0.17% for the SQ mode and MS/MS mode, respectively. The impact of the first mass filter in the MS/MS mode has a significant effect on the mass bias discrimination process and hence the accuracy of U isotopic ratios.

A low-cost total dissolution method for accurate determination of uranium and thorium isotopes in environmental samples (soil and sediment) was introduced, optimised and validated. The method included alkaline fusion based on sodium hydroxide (NaOH) and sodium peroxide (Na2O2), followed by sequential extraction chromatography separation and measurements with ICP-MS or alpha-particle spectrometry. The overall chemical recoveries for U and Th for the entire procedure were about 80% and 90%, respectively. The U-238 contribution from partial dissolution of the nickel crucibles accounted for about 80% of the total background activity.

The assessment of the origin of the anthropogenic contamination in marine regions impacted by other sources than global fallout is a challenge. This is the case of the west coast of Sweden, influenced by the liquid effluents released by the European Nuclear Reprocessing Plants through North Sea currents and by Baltic Sea local and regional sources, among others. This work focused on the study of anthropogenic actinides (236U, 237 Np and 239,240Pu) in seawater and biota from a region close to Gothenburg where radioactive wastes with an unknown composition were dumped in 1964. To this aim, a radiochemical procedure for the sequential extraction of U, Np and Pu from biota samples and the subsequent analysis of 236 U, 237 Np, 239 Pu and 240 Pu by Accelerator Mass Spectrometry was developed. The method was validated through the study of two reference materials provided by the International Atomic Energy Agency (IAEA): IAEA-446 (Baltic Sea seaweed) and IAEA-437 (Mediterranean Sea mussels). The 233U/236U atom ratio was also studied in the seawater samples. The obtained results indicate that the North Sea currents and global fallout are the major sources for 236 U, 237 Np and 239,240Pu to the studied area, without clear evidence of other local sources. Complementary, information on the Concentrations Factors (CF) in biota was obtained, for which the available information is very scarce. For seaweed, CF values of (4.07 +/- 0.90).103, 61 +/- 22 and 76 +/- 16 have been obtained for Pu, Np and U, respectively. Lower CF values of (3.37 +/- 0.78).102, 34 +/- 10 and 15.9 +/- 3.4 for Pu, Np and U, respectively, have been obtained for mussels.

Continental dust can be suspended and transported by the wind, reaching seawater masses far away from its source. The deposition of the aerosols on the ocean surface can alter the abundance of chemical species in the water column and contribute to element inventories in seafloor sediments. A major Saharan dust intrusion into the Western Mediterranean Sea was recorded at the DYFAMED site (Ligurian Sea) in 20th February 2004. We determined the influence of this dust event on the concentration of 30 minor and trace level elements (TE) in sinking particles collected by sediment traps deployed at 200 m and 1000 m depth, and how a dust flux event like this contributed to the exchange of TE, including Fe, with the water column during major dust events. With coupled sediment traps and aerosol samples, we assessed the short-term implications of dust events in the water column. The event produced a flux of fast (>111 m d(-1)) and slow ( < 20 m d(-1)) sinking dust particles, detected during 3 weeks at 200 m and 4 weeks at 1000 m depth. Additionally, the obtained results of element concentrations and particles flux show that a single dust deposition event can produce a sinking flux equivalent to annual deposition rates of elements relevant to biogeochemical cycles and/or pollution studies: (>60% for Cr and Cu, >70% for Al, > 80% for Ni and Zn, > 90% for V and Mn, > 100% for Fe and Pb). The corresponding Enrichment Factors (EF) for the minor and TE analyzed in the sediment traps during the dust event were calculated. EF was used to determine how minor and trace element concentrations in sinking particles vary. The values ranged between 0.35 and 421 in both 200 m and 1000 m sediment traps. For most of the analyzed elements, the obtained EF values were higher than 1. On the contrary, V, Y, Zr, Nb, and Ce showed EF similar to 1 while Cr, Ni, Cu, Zn, Sn, and Pb showed EF < 1. Despite the variability in the EF values, vertical fluxes integrated during the dust deposition event increased from 200 m to 1000 m, except for I, which decreased. This contrasts strongly with the element fluxes integrated for the complete sampling period, which decrease or increase from 200 m to 1000 m, depending on the element. This suggests that sinking dust particles were acting generally as sinks of the TE. We conclude that, apart from I, a substantial portion of the elements from atmospheric dust input from a single deposition event can reach the mesopelagic layer of the Western Mediterranean basin without increasing the budget of those elements in the water column.

Plutonium distribution was studied in an undisturbed sediment core sampled from the Tvaren bay in the vicinity of the Studsvik nuclear facility in Sweden. The complete analysis, including minor isotopes, of the Pu isotope composition (238Pu, 239Pu, oPu, 241Pu, 242Pu, and 244Pu) allowed us to establish the Pu origin in this area of the Baltic Sea and to reconstruct the Studsvik aquatic release history. The results show highly enriched 239Pu, probably originating from the Swedish nuclear program in the 1960s and 1970s and the handling of high burn-up nuclear fuel in the later years. In addition, the 244Pu/239Pu atomic ratio for the global fallout period between 1958 and 1965 is suggested to be (7.94 +/- 0.31)center dot 10-5. In the bottom layer of the sediment, dated 1953-1957, we detected a higher average 244Pu/239Pu ratio of (1.51 +/- 0.11)center dot 10-4, indicating the possible impact of the first US thermonuclear tests (1952-1958).

The activity concentrations and distribution of Cs-137, 238pu (239)I(-240)pu, Am-241,and Pb-210 was determined by the analysis of six sediment cores from the Baltic Sea and Kattegat. The chronology of the sediment cores has been used to evaluate the origin and time trend of the radionuclide sources in these sediments. The sediment cores were dated with a Pb-210 model and the results were validated with fallout peaks, assumed to originate from the global nuclear weapons testing and the Chernobyl accident. Source identification, using the isotopic and radionuclide activity ratios, showed that the Chernobyl accident is the main source of Cs-137 in the Baltic Sea; for Pu239+24 and Am-241 the dominant source was shown to be fallout from nuclear weapons tests. For (PU)-P-238 and 2(41)Am the Chernobyl accident had a significant impact on the direct fallout into the Baltic Proper, with up to a 65% contribution in the sediment slices dated to 1986. In these sediment slices the maximum activity ratios of (238)pu/(239+240)pu and (241)Am(/2394-240)pu were 0.314 +/- 0.008 and 1.29 +/- 0.06, respectively. The ratios clearly deviate from the corresponding ratios for global nuclear weapons fallout (around 0.028 and 0.54, respectively). Calculated inventories were 63 (175)Bq-m(-2) for 239+240PII, 2.8-7.8 for Pu-238 Bq-m(-2) and 0.92-44.4 kBq-m(-2) for Cs-137. Different fallout patterns for Cs-137 and plutonium isotopes from the Chernobyl accident were confirmed through depth profiles analyses. The maximum inventory of 137Cs was observed in the Bothnian Sea, while Chernobyl derived plutonium was found to be mostly present in Northern Baltic Proper. The radionuclides distribution in the depth profiles shows how contaminated water affects the sediment as it passes sampling stations according to the current circulation pattern in the Baltic Sea. Additionally, the effect of increased activity concentrations from of river discharges in the most contaminated area in the Bothnian Sea was observed. (C) 2017 Elsevier Ltd. All rights reserved.

The analytical method of Gd determination was developed with the aim to analyse Gd-148 in environmental and bioassay samples. It involves the use of anion exchange resin, extraction chromatography, and cation exchange resin. Alkaline fusion and calcium oxalate co-precipitation are used for solid samples dissolution and liquid samples preconcentration, respectively. Total method recovery was tested with natural Gd (Gd-157) using ICP-QQQ-MS. A maximum total recovery of 75 % was obtained.

Marine sediments bury similar to 160 Tg of organic carbon (OC) annually and represent an essential component of the global carbon cycle. OC burial is inherently multifactorial; however, in the past decade, the role of iron in regulating OC burial via the formation of organo-mineral associations, known as "rusty carbon sink," has been extensively studied. Despite widespread recognition, the origin of the OC preserved within these associations and the effect of the bottom-water oxygenation on their stability are still debated. Here, we investigate the rusty carbon sink in sediments collected across transects from the head to mouth of three Swedish fjords presenting contrasting bottom-water oxygenation regimes (the oxic Hake fjord, seasonally hypoxic Gullmar fjord, and anoxic By fjord). We found that the oxygenation regimes, the intensity of benthic iron cycling or the OC origin have little to no influence on the amount of OC bound to Fe (OC - Fe). The lack of correlation with any of the parameters studied, in combination with an increase in the OC - Fe in the fjords with riverine input suggest, at least partially, an allochthonous origin of these organo-mineral associations. Our results also show that the rusty carbon sink plays a modest role in the OC burial in these fjords (similar to 6% OC is bound to Fe). While these fjords still represent important OC burial hotspots with an average of similar to 35 g C m-2 buried annually, the OC burial is controlled by other sedimentary processes, such as the high mass accumulation rates found in these fjord systems.

We present an application of multi-isotopic fingerprints (i.e., U-236/U-238, U-233/U-236, U-236/I-129 and I-129/I-127) for the discovery of previously unrecognized sources of anthropogenic radioactivity. Our data indicate a source of reactor U-236 in the Baltic Sea in addition to inputs from the two European reprocessing plants and global fallout. This additional reactor U-236 may come from unreported discharges from Swedish nuclear research facilities as supported by high U-236 levels in sediment nearby Studsvik, or from accidental leakages of spent nuclear fuel disposed on the Baltic seafloor, either reported or unreported. Such leakages would indicate problems with the radiological safety of seafloor disposal, and may be accompanied by releases of other radionuclides. The results demonstrate the high sensitivity of multi-isotopic tracer systems, especially the U-233/U-236 signature, to distinguish environmental emissions of unrevealed radioactive releases for nuclear safeguards, emergency preparedness and environmental tracer studies. Anthropogenic activities lead to the accumulation of radioactive substances in the environment. Here the authors use multi-isotopic fingerprints of uranium and iodine to discover a previously unknown source of reactor uranium in the Baltic Sea, likely sourced from a Swedish nuclear facility.

Studsvik, a Swedish nuclear research facility, has been releasing aquatic radioactive discharges in the Baltic Sea, through the bay Tva center dot ren, since 1959. The permissible discharge levels are regulated by the Swedish Radiation Safety Authority (SSM) but only information about 60Co, 137Cs, 152Eu, total alpha and beta activities were re-ported up to 2002. Since then, the reports cover most a more comprehensive set of radionuclides. In this context, the seabed can be utilized as a chronological archive to investigate historical Studsvik releases. To this end, 23 sediment cores covering the whole area of the bay were studied and 5 of them were dated using 210Pb-dating methods. Since the discharges from Studsvik contain both plutonium and caesium, neither can be used to validate the 210Pb-dating method. Instead, stable lead with maximum deposition, known to be dated to 1970, was used. Cobalt-60, 137Cs, and 152Eu depth distributions were studied from the dated sediment cores and compared with reported levels of aquatic discharges. The expected sediment 137Cs-peak from the fallout from the Chornobyl accident was however smeared out, indicating an ongoing inflow of 137Cs with the Baltic seawater. Our findings show that reported releases of aquatic discharges of 60Co and 152Eu are consistent with measured sediment activity distribution. The sediments from the deepest parts of Tva center dot ren, with intact chronology and with a high time resolution, are ideal for investigating historical nuclear discharges and can be a tool to investigate unreported radionuclide releases. Dated sediment can in this way be a tool for nuclear safeguards to evaluate past and present activities in nuclear facilities.

Organic carbon (OC) burial efficiency, which relates the OC burial rate to respiration in the seafloor, is a critical parameter in the reconstruction of past marine primary productivities. The current accepted theory is that sediments underlying oxygen-deficient (anoxic) bottom waters have low respiration rates and high OC burial efficiencies. By combining novel in situ measurements in anoxic basins with reaction-transport modelling, we demonstrate that sediments underlying anoxic bottom waters have much higher respiration rates than commonly assumed. A major proportion of the carbon respiration is concentrated in the top millimeter-the so-called reactive surface layer-which is likely a feature in approximately 15% of the coastal seafloor. When re-evaluating previously published data in light of our results, we conclude that the impact of bottom-water anoxia on OC burial efficiencies in marine sediments is small. Consequently, reconstructions of past marine primary productivity in a predominantly anoxic ocean based on OC burial rates might be underestimated by up to an order of magnitude.

Fjords are net carbon sinks with high organic carbon (OC) burial rates; however, the key drivers of OC burial in these systems are not well constrained. To study the role of water column redox condition and OC composition on OC preservation in fjord sediments, we determined OC accumulation rates (OCAR), OC source, and OC degradation in three Swedish fjords with variable redox conditions (long-term oxic, seasonally hypoxic, and long-term anoxic). Average OCARs were variable between and within the fjords studied (2-122 g OC m-2 yr-1), but highest rates were at the mouth for each fjord. Based on a delta 13C mixing model, Swedish fjords bury predominantly marine-derived OC (similar to 83% of the total OC burial) likely because of relatively gentle slopes, low riverine discharge, and high marine inflow. Using a multi-biomarker approach (lignin, photosynthetic pigments, and total hydrolyzable amino acids) we found, terrestrially- and marine-derived OC were moderately degraded under the various redox conditions sampled, suggesting water column redox and OC source are not primary drivers of OC burial in these fjords. Rather, high sediment accumulation rates, common to fjords globally, lead to low oxygen exposure times, thus promoting efficient burial of OC regardless of its chemical composition. Fjords are net carbon sinks due in part to very high organic carbon burial rates. Despite being important in the regulation of earth's climate, the drivers of organic carbon burial in fjords are not well constrained. Here, we characterize the organic carbon buried in Swedish fjord sediments under different oxygen regimes (long-term oxic, seasonally hypoxic, and long-term anoxic) using bulk elemental and biomarker analyses. These fjords effectively bury organic carbon regardless of organic carbon source and water column oxygen conditions, likely because of high sediment accumulation rates. Fjords represent distinctive coastal systems with the capacity to retain reactive organic carbon, underscoring the importance of exploring these ecosystems in the context of global change. Swedish fjords bury primarily marine-derived organic carbon under long-term oxic, seasonally hypoxic, and long-term anoxic water columns Organic carbon burial in Swedish fjords is largely controlled by sediment accumulation rate which can limit oxygen exposure time Marine-dominated fjords are uniquely efficient sinks of labile organic carbon

Nuclear industry workers exposed to uranium aerosols may risk kidney damage and radiation-induced cancer. This warrants the need for well-established dose and risk assessments, which can be greatly improved by using material-specific absorption parameters in the ICRP Human Respiratory Tract Model. The present study focuses on the evaluation of the slow dissolution rate (s(s), d(-1)), a parameter that is difficult to quantify with in vitro dissolution studies, especially for more insoluble uranium compounds. A long-term follow-up of urinary excretion after the cessation of chronic inhalation exposure can provide a better estimate of the slow-rate dissolution. In this study, two workers, previously working for >20 y at a nuclear fuel fabrication plant, provided urine samples regularly for up to 6 y. One individual had worked at the pelletizing workshop with the known presence of uranium dioxide (UO2) and triuranium octoxide (U3O8). The second individual worked at the conversion workshop where multiple compounds, including uranium hexafluoride (UF6), uranium dioxide (UO2), ammonium uranyl carbonate, and AUC [UO2CO3<middle dot>2(NH4)(2)CO3], are present. Data on uranium concentration in urine during working years were also available for both workers. The daily excretion of uranium by urine was characterized by applying non-linear least square regression fitting to the urinary data. Material-specific parameters, such as the activity median aerodynamic diameter (AMAD), the respiratory tract absorption parameters, rapid fraction (f(r),), rapid dissolution rate (s(r), d(-1)), and slow dissolution rate (s(s), d(-1)) and alimentary tract transfer factor (f(A)) acquired from previous work along with default absorption types, were applied to urine data, and the goodness of fit was evaluated. Thereafter intake estimates and dose calculations were performed. For the ex-pelletizing worker, a one-compartment model with a clearance half-time of 662 +/- 100 d (s(s) = 0.0010 d(-1)) best represented the urinary data. For the ex-conversion worker, a two-compartment model with a major [93% of the initial urinary excretion (A(0))] fast compartment with a clearance half-time of 1.3 +/- 0.4 d (s(r) = 0.5 d(-1)) and a minor (7% of A(0)) slow compartment with a half-time of 394 +/- 241 d (s(s) = 0.002 d(-1)) provided the best fit. The results from the data-fitting of urinary data to biokinetic models for the ex-conversion worker demonstrated that in vitro derived experimental parameters (AMAD = 20 mu m, f(r) = 0.32, s(r) = 27 d(-1), s(s) = 0.0008 d(-1), f (A) = 0.005) from our previous work best represented the urinary data. This resulted in an estimated intake rate of 0.66 Bq d(-1). The results from the data-fitting of urinary data to biokinetic models for the ex-pelletizing worker indicated that the experimental parameters (AMAD = 10 mu m and 20 mu m, f(r) = 0.008, s(r) = 12 d(-1), f(A) = 0.00019) from our previous dissolution studies with the slow rate parameter step-wise optimized to urine-data (s(s) = 0.0008 d(-1)) gave the best fit. This resulted in an estimated intake rate of 5 Bq d(-1). Experimental parameters derived from in vitro dissolution studies provided the best fit for the subject retired from work at the conversion workshop, where inhalation exposure to a mix of soluble (e.g., AUC, UF6) and relatively insoluble aerosol (e.g., UO2) can be assumed. For the subject retired from work at the pelletizing workshop, which involved exposure to relatively insoluble aerosols (UO2 and U3O8), a considerably higher s(s) than obtained in dissolution studies provided a better representation of the urinary data and was comparable to reported s(s) values for UO2 and U3O8 in other studies. This implies that in vitro dissolution studies of insoluble material can be uncertain. When evaluating the results from the retrospective fitting of urine data, it is evident that the urine samples acquired after cessation of exposure provide less fluctuation. Long-term follow-up of uranium excretion after cessation of exposure is a good alternative for determining absorption parameters and can be considered the most viable way for determining the slow rate for more insoluble material.

Uranium aerosol exposure can be a health risk factor for workers in the nuclear fuel industry. Good knowledge about aerosol dissolution and absorption characteristics in the gastrointestinal tract is imperative for solid dose assessments and risk management. In this study, an in vitro dissolution model of the GI tract was used to experimentally study solubility of size-fractionated aerosols. The aerosols were collected from four major workshops in a nuclear fuel fabrication plant where uranium compounds such as uranium hexafluoride (UF6), uranium dioxide (UO2), ammonium uranyl carbonate, AUC [UO2CO3 center dot 2(NH4)(2)CO3] and triuranium octoxide (U3O8) are present. The alimentary tract transfer factor, f(A), was estimated for the aerosols sampled in the study. The transfer factor was derived from the dissolution in the small intestine in combination with data on absorption of soluble uranium. Results from the conversion workshop indicated a f(A) in line with what is recommended (0.004) by the ICRP for inhalation exposure to Type M materials. Obtained transfer factors, f(A), for the powder preparation and pelletizing workshops where UO2 and U3O8 are handled are lower for inhalation and much lower for ingestion than those recommended by the ICRP for Type M/S materials f(A) = 0.00029 and 0.00016 vs. 0.0006 and 0.002, respectively. The results for ingestion and inhalation f(A) indicate that ICRPs conservative recommendation of f(A) for inhalation exposure is applicable to both ingestion and inhalation of insoluble material in this study. The dissolution- and subsequent absorption-dependence on particle size showed correlation only for one of the workshops (pelletizing). The absence of correlation at the other workshops may be an effect of multiple chemical compounds with different size distribution and/or the reported presence of agglomerated particles at higher cut points having more impact on the dissolution than particle size. The impact on dose coefficients [committed effective dose (CED) per Bq] of using experimental f(A) vs. using default f(A) recommended by the ICRP for the uranium compounds of interest for inhalation exposure was not significant for any of the workshops. However, a significant impact on CED for ingestion exposure was observed for all workshops when comparing with CED estimated for insoluble material using ICRP default f(A). This indicates that the use of experimentally derived site-specific f(A) can improve dose assessments. It is essential to acquire site-specific estimates of the dissolution and absorption of uranium aerosols as this provides more realistic and accurate dose- and risk-estimates of worker exposure. In this study, the results indicate that ICRPs recommendations for ingestion of insoluble material might overestimate absorption and that the lower f(A) found for inhalation could be more realistic for both inhalation and ingestion of insoluble material.