Irish Sea Sediments Research Articles

Independent measurements of 129I content in environmental reference materials using accelerator and thermal ionization mass spectrometry

Iodine environmental measurement programs are in need of new materials with certified 129I activity. Frequently 129I measurements are validated in the literature using the standard material IAEA-375, Chernobyl soil, which is the only soil/sediment material with a recommended 129I activity. IAEA-375 has not been available for purchase since 2010. This study is an extension of previous work at INL to include four additional standard materials that are commercially available (NIST materials: RM 8704, Buffalo River sediment, SRM 2710a, Montana I soil, and IAEA materials: SL-1, lake sediment, IAEA-385, Irish Sea sediment). These materials have certified or recommended activities for a variety of radionuclides but not for 129I. This paper reports a comparison of accelerator mass spectrometry (AMS) and thermal ionization mass spectrometry (TIMS) data for 129I activity, as well as the 129/127I ratios for these standards to assist in identifying a suitable alternative for IAEA-375. Two independent chemical separation and mass spectrometric analysis techniques have been applied in an effort to corroborate the data. Both methods were validated via analyses of IAEA-375 for 129I and show good agreement with the recommended activity of 1.7 × 10−3 Bq kg−1 for 129I; (1.6 × 10−3 Bq kg−1 by AMS and 1.8 × 10−3 Bq kg−1 by TIMS) with both sets of results within the 95% confidence interval of the recommended value.

Extremely low radioactivity in marine sediment of coral reefs and its mechanism

Radionuclides are hazardous materials which impose ionizing radiation on humans and are valuable proxies for tracking environmental processes. Radionuclides are widely reported in global marine sediments, which are recognized as the final destination of radionuclides. As one of the typical marine ecosystems, coral reefs are “hotspots” of high biodiversity providing rich biological resources and significant tourist sites for humans. Seafood consumption and SCUBA diving would induce internal and external radiation on humans, respectively. However, radioactivity is rarely studied in coral reef ecosystems. Here, we exhibited radionuclides in marine sediments collected from the fringing and atoll reefs with a latitudinal coverage of 14° (~1500 km) in the South China Sea (SCS). Naturally occurring radionuclides (40K, 226Ra, 228Ra, and, 238U) were quantified by Standard River Sediment (GBW08304a) and were validated by Irish Sea Sediment (IAEA-385) using High Purity Germanium (HPGe) γ spectrometry (Canberra BE6530). The energy resolution of HPGe γ-spectrometry (~2 keV) is much better than that of NaI γ-spectrometry (~50 keV). Overall, radioactivity in marine sediments was in the order of 238U (28.96 Bq/kg) >40K (24.36 Bq/kg) >228Ra (5.08 Bq/kg) >226Ra (3.34 Bq/kg). Radioactivity was higher in marine sediments collected from the fringing reefs than the atoll reefs due to the influence of terrigenous minerals in the fringing reefs. The occurrence of terrigenous minerals was confirmed by the mineral components (K-feldspar, illite, and quartz) using X-ray diffraction analysis. Additionally, the rare earth elements (REE) are generally used to trace terrigenous inputs. In the present study, the ranking pattern of the 40K activity was consistent with the concentration of REE in marine sediments (sediments outside the coral reef regions > sediments from fringing reefs > sediments from atoll reefs), giving supporting evidence of the influence of terrigenous minerals. A comparison of radionuclides in marine sediments from coral reefs and other sea regions indicated that the radioactive level (Radium equivalent activity, Ra eq) of marine sediment in coral reefs was only 1%−10% of that of other marine sediments and global soil. The value of Ra eq in marine sediments collected from coral reefs (3−42 Bq/kg) was also lower than that in marine sediments collected from the pristine environment of the Arctic Ocean (70.62 Bq/kg) and Southern Ocean (76.92 Bq/kg). Particularly, the mean value of Ra eq in marine sediments of the atoll reefs in the SCS (3.97 Bq/kg) was less than 5% of that in global average soil (108.70 Bq/kg). Therefore, radioactivity in marine sediment was extremely low in coral reefs relative to other sea regions. Marine sediments in coral reefs had three unique characteristics of low 40K activity, low 226Ra and 228Ra activity, and low 226Ra/238U ratio. It was worth noting that the abnormally low 226Ra/238U activity ratio (<0.1) of marine sediments was observed in the atoll reefs and was attributed to the biological process of active uptake of 226Ra and 238U from seawater by coral polyps rather than the ingrowth process of the 238U-230Th-226Ra decay chain. The mechanism of radioactive characteristics in marine sediments was attributed to the fragmentation and weathering of biominerals in coral reefs in contrast to the weathering and subsequent transport of soil and rocks in other marine sediments outside the coral reef region. These three characteristics have potential to be novel geochemical proxies for tracking particle dynamics in coral reefs in addition to other traditional approaches including the Al, Ti, REE, and mineral components.

Sequential analyses of actinides in large-size soil and sediment samples with total sample dissolution

There is a growing demand for the determination of actinides in soil and sediment samples for environmental monitoring and tracing, radiological protection, and nuclear forensic reasons. A total sample dissolution method based on lithium metaborate fusion, followed by sequential column chromatography separation, was developed for simultaneous determination of Pu, Am and Cm isotopes in large-size environmental samples by alpha spectrometry and mass spectrometric techniques. The overall recoveries of both Pu and Am for the entire procedure were higher than 70% for large-size soil samples. The method was validated using 20 g of soil samples spiked with known amounts of 239Pu and 241Am as well as the certified reference materials IAEA-384 (Fangataufa Lagoon sediment) and IAEA-385 (Irish Sea sediment). All the measured results agreed very well with the expected values.

Classifying seabed sediment type using simulated tidal-induced bed shear stress

Abstract An ability to estimate the large-scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications. In some physical (e.g., morphodynamic) models, knowledge of seabed sediment type is important for inputting spatially-varying bed roughness, and in biological studies, an ability to estimate the distribution of seabed sediment benefits habitat mapping (e.g., scallop dredging). Although shelf sea sediment motion is complex, driven by a combination of tidal currents, waves, and wind-driven currents, in many tidally energetic seas, such as the Irish Sea, long-term seabed sediment transport is dominated by tidal currents. We compare observations of seabed sediment grain size from 242 Irish Sea seabed samples with simulated tidal-induced bed shear stress from a three-dimensional tidal model (ROMS) to quantitatively define the relationship between observed grain size and simulated bed shear stress. With focus on the median grain size of well-sorted seabed sediment samples, we present predictive maps of the distribution of seabed sediment classes in the Irish Sea, ranging from mud to gravel. When compared with the distribution of well-sorted sediment classifications (mud, sand and gravel) from the British Geological Survey digital seabed sediment map of Irish Sea sediments (DigSBS250), this ‘grain size tidal current proxy’ (GSTCP) correctly estimates the observed seabed sediment classification in over 73% of the area.

Temporal Trend in the Transfer of Sellafield-Derived 14C into Different Size Fractions of the Carbonate Component of NE Irish Sea Sediment

From 1994 onwards, radiocarbon discharges from the Sellafield nuclear fuel reprocessing plant have been made largely to the northeast Irish Sea. They represent the largest contributor to UK and European populations of the collective dose commitment derived from the entire nuclear industry discharges. Consequently, it is important to understand the long-term fate of 14C in the marine environment. Research undertaken in 2000 suggested that the carbonate component of northeast Irish Sea sediments would increase in 14C activity as mollusk shells, which have become enriched in Sellafield-derived 14C, are broken down by physical processes including wave action and incorporated into intertidal and subtidal sediments. The current study, undertaken in 2011, tested this hypothesis. The results demonstrate significant increases in 14C enrichments found in whole mussel shells compared to those measured in 2000. Additionally, in 2000, there was an enrichment above ambient background within only the largest size fraction (&gt;500 μm) of the intertidal inorganic sediment at Nethertown and Flimby (north of Sellafield). In comparison, the present study has demonstrated 14C enrichments above ambient background in most size fractions at sites up to 40 km north of Sellafield, confirming the hypothesis set out more than a decade ago.

An improved procedure for the determination of 210Po by alpha spectrometry in sediments samples from Danube Delta

The aim of this work is to find the optimal procedure for 210Po leaching from sediment samples. An improved method is described, the optimization consisting in a substantial reduction of leaching time. The method was tested on IAEA standard reference materials and compared with the classical procedure. The repeatability was estimated by analyzing seven duplicates of IAEA 385 Irish Sea sediment. However, the results are satisfactory only when the method is applied for sediments with high organic content. For silicates, a mixture of three acids was used for a complete digestion.

Artificial radionuclides in the Irish Sea from Sellafield: remobilisation revisited

Measured concentrations of Cs-137, tritium, Tc-99, Pu-239+240 and Am-241 in representative materials from the Irish Sea were investigated with reference to continuing remobilisation from sediments. Long time series of monitoring data since the 1960s were employed. Cs-137 in sea water and fish shows peaks in concentrations normalised to discharge rate (NACs) from 1985 to 1989. This is consistent with the time needed for dispersion in sea water following the preceding reductions in discharges; continuing enhancements of NACs above pre-1970s levels follow, consistent with the effect of activity remobilised from sediment. It is estimated that about 300 TBq of Cs-137 was remobilised from the immediate tidal area around Sellafield from 1989 to 2009. The enhancements in concentrations continue to this day, with the effect of remobilisation at present being ∼6 TBq y−1, approximately doubling the effect of direct discharges. To provide an indication for the future, the rate of Cs-137 remobilisation is decreasing with a half-time of ∼6 years. The data for tritium and Tc-99 were examined in view of the interest in these radionuclides. The concentrations broadly reflect the levels of discharges and the need for dispersion. As expected, there is no evidence of sustained remobilisation of tritium, due to its mobility (or low Kd). The same lack of evidence was found to apply for Tc-99 despite known sorption of a small proportion of the discharged activity by Irish Sea sediments. Pu-239+240, by contrast, shows much evidence of the effect of remobilisation; concentrations in sea water near Sellafield have reduced much more slowly than discharges. At Southerness, ∼50 km away, there was no significant reduction in sea water concentrations from 1985 to 1996, and winkles showed an increase then decrease in concentrations over this period, consistent with a spreading of activity. This effect was replicated in mud at Garlieston, ∼70 km from Sellafield. For Am-241, the rate of grow-in from Pu-241 has dominated direct discharges since the late 1970s. Grow-in continues today in the Irish Sea at the rate of ∼8 TBq y−1, ∼200 times the rate of direct discharge. Winkles at Southerness show evidence of a spreading effect of Am-241, with an increase then decrease from 1985 to 1996. At Garlieston there was an increase in concentrations in mud from 1985 to 1997, and at Carlingford in Northern Ireland the concentration of Am-241 in mud appears to be increasing still. This effect of the spread of activity away from Sellafield may continue, at least in the near future.

Determination of U, Pu and Am isotopes in Irish Sea sediment by a combination of AMS and radiometric methods

Samples from a marine sediment core from the Irish Sea (54.416 N, 3.563 W) were analyzed for the isotopic composition of uranium, plutonium and americium by a combination of radiometric methods and AMS. The radiochemical procedure consisted of a Pu separation step by anion exchange, subsequent U separation by extraction chromatography using UTEVA ® and finally Am separation with TRU ® Resin. Additionally to radiometric determination of these isotopes by alpha spectrometry, the separated samples were also used for the determination of 236U/ 238U and plutonium isotope ratios by Accelerator Mass Spectrometry (AMS) at the VERA facility.

Rapid isolation of plutonium in environmental solid samples using sequential injection anion exchange chromatography followed by detection with inductively coupled plasma mass spectrometry

This paper reports an automated analytical method for rapid determination of plutonium isotopes ( 239Pu and 240Pu) in environmental solid extracts. Anion exchange chromatographic columns were incorporated in a sequential injection (SI) system to undertake the automated separation of plutonium from matrix and interfering elements. The analytical results most distinctly demonstrated that the crosslinkage of the anion exchanger is a key parameter controlling the separation efficiency. AG 1-×4 type resin was selected as the most suitable sorbent material for analyte separation. Investigation of column size effect upon the separation efficiency revealed that small-sized (2 mL) columns sufficed to handle up to 50 g of environmental soil samples. Under the optimum conditions, chemical yields of plutonium exceeded 90% and the decontamination factors for uranium, thorium and lead ranged from 10 3 to 10 4. The determination of plutonium isotopes in three standard/certified reference materials (IAEA-375 soil, IAEA-135 sediment and NIST-4359 seaweed) and two reference samples (Irish Sea sediment and Danish soil) revealed a good agreement with reference/certified values. The SI column-separation method is straightforward and less labor intensive as compared with batch-wise anion exchange chromatographic procedures. Besides, the automated method features low consumption of ion-exchanger and reagents for column washing and elution, with the consequent decrease in the generation of acidic waste, thus bearing green chemical credentials.

Modelling the reworking effects of bioturbation on the incorporation of radionuclides into the sediment column: implications for the fate of particle-reactive radionuclides in Irish Sea sediments

A microcosm laboratory experiment was conducted to determine the impact of biological reworking by the ragworm Nereis diversicolor on the redistribution of particle-bound radionuclides deposited at the sediment–water interface. Over the course of the 40-day experiment, as much as 35% of a 137Cs-labelled particulate tracer deposited on the sediment surface was redistributed to depths of up to 11 cm by the polychaete. Three different reworking models were employed to model the profiles and quantify the biodiffusion and biotransport coefficients: a gallery-diffuser model, a continuous sub-surface egestion model and a biodiffusion model. Although the biodiffusion coefficients obtained for each model were quite similar, the continuous sub-surface egestion model provided the best fit to the data. The average biodiffusion coefficient, at 1.8 ± 0.9 cm 2 y −1, is in good agreement with the values quoted by other workers on the bioturbation effects of this polychaete species. The corresponding value for the biotransport coefficient was found to be 0.9 ± 0.4 cm y −1. The effects of non-local mixing were incorporated in a model to describe the temporal evolution of measured 99Tc and 60Co radionuclide sediment profiles in the eastern Irish Sea, influenced by radioactive waste discharged from the Sellafield reprocessing plant. Reworking conditions in the sediment column were simulated by considering an upper mixed layer, an exponentially decreasing diffusion coefficient, and appropriate biotransport coefficients to account for non-local mixing. The diffusion coefficients calculated from the 99Tc and 60Co cores were in the range 2–14 cm 2 y −1, which are consistent with the values found by other workers in the same marine area, while the biotransport coefficients were similar to those obtained for a variety of macrobenthic organisms in controlled laboratories and field studies.

Identification and characterisation of radioactive particles in salt marsh sediments

Radionuclides from authorized low level radioactive effluent discharges from the nuclear fuel reprocessing plant at Sellafield, UK, are present in the Irish Sea sediments. The distribution of radionuclides in salt marsh sediment profiles can be related to the discharge history from Sellafield. Radioactive particles, from the intertidal salt marsh sediments in the Esk estuary (10 km from Sellafield), have been isolated and investigated. Autoradiography and heavy liquid density separation were used to find and isolate these particles. Scanning electron microscopy, combined with energy dispersive X-ray analysis (SEM-EDX), was used to obtain information on the morphology and elemental composition of the particles, and alpha spectrometry for radionuclide composition. Particles are typically 1 — 20 μm size. Elemental analysis suggests that they are composed mainly of uranium. Alpha spectrometry shows that they have been irradiated, and transuranium nuclides (Pu, Am, Cm) can be identified in them.

Sensitivity of DF-ICP-MS, PERALS and alpha-spectrometry for the determination of actinides: A comparison

We applied three techniques (DF-ICP-MS, PERALS and alpha-spectrometry) for the determination of minor actinides at environmental levels. For each method the limit of detection and the resolution were estimated in order to study the content and isotopic composition of the actinides. Two international reference materials, IAEA-135 (Irish Sea Sediment) and IAEA-300 (Baltic Sea sediment) were analyzed for activity concentrations of 238Pu, 239Pu, 240Pu, 241Pu and 241Am. The sensitivities of the three determination techniques were compared.

A new Certified Reference Material for radionuclides in Irish sea sediment (IAEA-385)

A new Certified Reference Material (CRM) for radionuclides in sediment (IAEA-385) is described and the results of the certification process are presented. Eleven radionuclides ( 40K, 137Cs, 226Ra, 228Ra, 230Th, 232Th, 234U, 238U, 238Pu, 239+240Pu and 241Am) have been certified and information mass activities with 95% confidence intervals are given for seven other radionuclides ( 90Sr, 210Pb( 210Po), 235U, 239Pu, 240Pu and 241Pu). Results for less frequently reported radionuclides ( 60Co, 99Tc, 134Cs, 155Eu, 224Ra and 239Np) and information on some activity and mass ratios are also reported. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in sediment samples, for the development and validation of analytical methods and for training purposes.

Application of inductively coupled plasma sector field mass spectrometry for low-level environmental americium-241 analysis

An improved and novel sample preparation method for 241Am analysis by inductively coupled plasma sector field mass spectrometry has been developed. The procedure involves a selective CaF 2 pre-concentration followed by an extraction chromatographic separation using TRU™ resin. The achieved absolute detection limit of 0.86 fg (0.11 mBq) is comparable to that of alpha spectrometry (0.1 mBq) and suitable for low-level environmental measurements. Analysis of different kinds of environmental standard reference materials (IAEA-384 – Fangataufa lagoon sediment, IAEA-385 – Irish Sea sediment and IAEA-308 – Mixed seaweed from the Mediterranean Sea) and alpha spectrometry were used to validate the procedure. The chemical recovery of sample preparation ranged between 72 and 94%. The results obtained are in good agreement with reference values and those measured by alpha spectrometry. The proposed method offers a rapid and less labor-intensive possibility for environmental 241Am analysis than the conventionally applied radioanalytical techniques.

Redissolution of caesium and plutonium from Irish Sea sediments: A comparison between different modelling approaches

Two models with different conceptual and numerical approaches have been used to simulate the dispersion of radionuclides released from Sellafield nuclear fuel reprocessing plant. The first is a long-term box-model for simulating dispersion from Sellafield to the Arctic environment in which water fluxes between boxes are obtained from basic oceanographic information. Water-sediment radionuclide exchanges are described through sedimentation and remobilisation processes on the basis of equilibrium distribution coefficients. The second model is a 3D high-resolution model that explicitly solves tidal mixing and suspended sediment transport in the Irish Sea. Exchanges of radionuclides between the liquid and solid phases are now described in terms of kinetic rates. Thus, this model has a general applicability and can be used in situations out from equilibrium. Both models have been used to simulate the dispersion of Cs and Pu in the Irish Sea. Results from the two models are comparable, being differences in the results smaller than should be expected from the very different modelling approaches.

Diagenetic reactivity of the plutonium in marine anoxic sediments (Cumbrian mud patch - eastern Irish Sea)

An extensive diagenetic study carried out on a sediment core collected in the Cumbrian mud patch off the Sellafield nuclear reprocessing plant, is presented. Sequential leaching data, using a thoroughly validated protocol specifically designed to prevent any resorption of the released plutonium in the course of the extraction, demonstrate that a significant proportion of the plutonium is loosely bound to sites that readily exchange with seawater, oxidise upon oxygenated water contact (reactive sulphides) or easily dissolve upon changes in pH. Such a result contradicts many previous sequential extraction studies which have reported that little of the plutonium in Irish Sea sediments is in a readily available form. The profile of dissolved plutonium in pore waters indicates an active uptake process at depth, probably linked to sulphide (Acid Volatile Sulphide) precipitation. These reactive sulphides are liable to act as source of plutonium to the overlying water if they are brought close the interface by bioturbation or in contact with oxygenated seawater by burrowing activity.

The distribution and transport of Sellafield derived 137Cs and 241Am to western Irish Sea sediments

Sellafield derived 137Cs and 241Am were analysed in surficial sediments at 23 sites in the western Irish Sea. Concentrations varied between 3–175 Bq 137Cs/kg and 1–147 Bq 241Am/kg. There are two distinct basins in the western Irish Sea separated by an area of restricted depth and this bathymetry is reflected in the radionuclide concentrations. Highest concentrations were found in the northerly samples and substantially lower concentrations further south. This pattern of distribution can be explained by the predominantly northerly residual flow and the existence of seasonal stratification in this area of weak tides. 137Cs/ 241Am ratios were also highest in the northern basin, and it is suggested that this is caused by differences in the mechanisms of transport of the two elements. The direct physical migration of contaminated particles from the eastern Irish Sea is the dominant transport mechanism in the north of the study area, whereas transport in the dissolved phase is most important to the southern region. Concentrations of both elements were best correlated with the percentage <15 μm particulate fraction suggesting that particles within this range are most important for direct transport and scavenging from the soluble phase.

Non-destructive characterisation of low radioactive particles from Irish Sea sediment by micro X-ray synchrotron radiation techniques: micro X-ray fluorescence (μ-XRF) and micro X-ray absorption near edge structure (μ-XANES) spectroscopy

Three radioactive uranium-rich particles were isolated from an Irish Sea sediment core using solid state nuclear track detection. Bulk analysis of the 24–26 cm core layer showed environmentally significant Pu and Am activities and concentrations. Morphology, elemental composition and uranium oxidation states of the particles were studied with electron microscopy and X-ray applications μ-XRF and μ-XANES. The results indicated that two of the particles were nuclear fuel debris, and one of them was of natural origin. The uranium in the particles was found to be in two oxidation states at different percentages: 60–66% as UIV and 34–40% as UVI.

14C and delta13C characteristics of organic matter and carbonate in saltmarsh sediments from south west Scotland.

The distribution of contaminant radionuclides from the Sellafield nuclear fuel reprocessing plant was used to establish chronologies for three saltmarsh sediment cores from south west Scotland. delta(13)C and (14)C analyses indicated that the cores provided a useful archive record of variations in input of organic matter and carbonate. The results imply that prior to major releases of contaminant (14)C from Sellafield, the (14)C specific activity of organic matter in Irish Sea offshore sediments was about 24 Bq kg(-1) C, while that of the carbonate component was below the limit of detection. These results provide baseline data for modelling the uptake of contaminant (14)C by the Irish Sea sediment system. The study confirmed that small(13)C analyses provide a sensitive means of apportioning the origin of saltmarsh organic matter between C(3) terrigenous plants, C(4) terrigenous plants and suspended particulate marine organic matter. For the <2 mm fraction of sediment, a clear pattern of decreasing marine organic input was observed in response to increasing elevation of the marsh surface as a result of sediment accumulation. Bulk sediment, including detrital vegetation, had a dominant input from terrigenous plants. The combined use of delta(13)C and (14)C data revealed that organic matter in the marine organic component of the <2 mm fraction of contemporary surface sediments of the saltmarshes is dominated by recycled old organic material.

Iodine-129 and Caesium-137 in Chernobyl contaminated soil and their chemical fractionation

Soil samples from areas in Belarus, Russia and Sweden contaminated by the Chernobyl accident were analysed for 129I by radiochemical neutron activation analysis, as well as for 137Cs by gamma-spectrometry. The atomic ratio of 129I/ 137Cs in the upper layer of the examined soil cores ranged from 0.10 to 0.30, with an average of 0.18, and no correlation between 129I/ 137Cs ratio and the distance from Chernobyl reactor to sampling location was observed. It seems feasible to use the 129I/ 137Cs ratio to reconstruct the deposition pattern of 131I in these areas. The association of 129I and 137Cs in the Chernobyl soil and Irish Sea sediment was investigated by a sequential extraction method. Similar speciation of 129I in the Chernobyl soil and Irish Sea sediment was found. Approximately 70% of 129I is bound to oxides and organic matter, and 10–20% is in the readily available phase, while most of the 137Cs (73%) in Chernobyl soil remains in the extraction residue.