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PubMed2004

Time-resolved laser fluorescence spectroscopy study on the interaction of curium(III) with Desulfovibrio äspöensis DSM 10631T.

The influence of microorganisms on migration processes of actinides has to be taken into account for the risk assessment of potential high-level nuclear waste disposal sites. Therefore it is necessary to characterize the actinide-bacteria species formed and to elucidate the reaction mechanisms involved. This work is focused on the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis (D. äspöensis) DSM 10631T which frequently occurs in the deep granitic rock aquifers at the Aspö Hard Rock Laboratory (Aspö HRL), Sweden. We chose Cm(III) due to its high fluorescence spectroscopic sensitivity as a model system for exploring the interactions of trivalent actinides with D. äspöensis in the trace concentration range of 3 x 10(-7) mol/L. A time-resolved laser fluorescence spectroscopy (TRLFS) study has been carried out in the pH range from 3.00 to 7.55 in 0.154 mol/L NaCl. We interpret the pH dependence of the emission spectra with a biosorption forming an inner-sphere surface complex of Cm(III) onto the D. äspöensis cell envelope. This Cm(III)-D. äspöensis-surface complex is characterized by its emission spectrum (peak maximum at 600.1 nm) and its fluorescence lifetime (162 +/- 5 micros). No evidence was found for incorporation of Cm(III) into the bacterial cells under the chosen experimental conditions.

Adsorption↗
PubMed2001

A refinement of the biofilm formation method for waste forms stability evaluation.

A refinement of the biofilm formation method for waste form stability evaluation was carried out in this study. Refinement of the biofilm formation method became necessary because of the reduced contrast in degradation between control and experimental samples. The reduction in contrast was occasioned by the long duration of exposure (12 days) of the control samples to sterile medium of low pH in the first stage. Results of evaluation carried out reveal that the duration of the first stage of the biofilm formation method can be reduced to 24 h, with substantial increase in the contrast between degradations experienced by control and experimental samples. Reduction of the first stage can be done without compromising the efficiency of the inoculation process, which the longer duration of the first stage was originally intended to ensure. A doubt as to actual formation of biofilms on experimental samples, resulting from the use of non-sterile tubings and glass wares in the second stage, was also addressed in this study. Results reveal that substantial attachment of microbes occur on the surfaces of experimental samples in the first stage, thus any supply of microbes via the tubings and glass wares in the second stage is only additional and inconsequential.

Acidithiobacillus thiooxidans↗
PubMed2003

Study of the contaminant transport into granite microfractures using nuclear ion beam techniques.

Hydrated bentonite is a very plastic material and it is expected to enter in the rock microfractures at the granite/bentonite boundary of a deep geological high-level waste repository. This process is enhanced by the high swelling pressure of the clay. Since bentonite has a very good sorption capability for many radionuclides, the displacement of the clay might lead to a "clay-mediated" contaminant transport into the rock. The aim of this work is to study the contaminant transport into granite microfractures using nuclear ion beam techniques, and to determine to what extent the clay can favour it. To do so, bentonite previously doped with uranium, cesium and europium was put in contact with the surface of granite sheets. Granite sheets contacted with non-doped bentonite and with radionuclide solutions were also prepared as references. This allowed analysing the differences in the diffusion behaviour of the three systems: clay, radionuclides and clay plus radionuclides. A combination of Rutherford backscattering spectrometry (RBS) and other nuclear ion-beam techniques such as particle-induced X-ray emission (PIXE) and microPIXE was used to study the depth and lateral distribution of clay and contaminants inside granite. It was also tried to evaluate not only the diffusion depth and diffusion coefficients but also the different areas of the granite where the diffusants have a preferential access.

Aluminum Silicates↗
PubMed2006

Sequential separation of lanthanides, thorium and uranium using novel solid phase extraction method from high acidic nuclear wastes.

A novel grafted polymer for selective extraction and sequential separation of lanthanides, thorium and uranium from high acidic wastes has been developed by grafting Merrifield chloromethylated (MCM) resin with octyl(phenyl)-N,N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) (MCM-CMPO). The grafting process is well characterized using FT-IR spectroscopy, (31)P and (13)C CPMAS (cross-polarized magic angle spin) NMR spectroscopy and CHNPS elemental analysis. The influence of various physico-chemical parameters during metal ion extraction by the resin phase are studied and optimized by both static and dynamic methods. The resin shows very high sorption capacity values of 0.960mmolg(-1) for U(VI), 0.984mmolg(-1) for Th(IV), 0.488mmolg(-1) for La(III) and 0.502mmolg(-1) for Nd(III) under optimum HNO(3) medium, respectively. The grafted polymer shows faster rate exchange kinetics (<5min is sufficient for 50% extraction) and greater preconcentration ability, with reusability exceeding 20 cycles. During desorption process, sequential separation of the analytes is possible with varying eluting agents. The developed grafted resin has been successfully applied in extracting Th(IV) from high matrix monazite sand, U(VI) and Th(IV) from simulated nuclear spent fuel mixtures. All the analytical data is based on triplicate analysis and measurements are within 3.5% rsd reflecting the reproducibility and reliability of the developed method.

Lanthanoid Series Elements↗
PubMed2005

Effect of pH and aging time on the kinetic dissociation of 243Am(III) from humic acid-coated gamma-Al2O3: a chelating resin exchange study.

The chelating resin was studied to assess its influence on metal availability and mobility in the environment. The association of organic-inorganic colloid-borne trace elements was investigated in this work. The radionuclide 243Am(III) was chosen as the representative and chemical homologue for trivalent lanthanide and actinide ions present in radioactive nuclear waste. The kinetic dissociation behavior of 243Am(III) from humic acid-coated gamma-Al2O3 was studied at pH values of 4.0 +/- 0.1, 5.0 +/- 0.2, and 6.0 +/- 0.2 with a contact time of 2 days after the addition of a chelating cation exchanger resin. The concentrations of the components were: 243Am(III) 3.0 x 10(-7) mol/L, gamma-Al2O3 0.5 g/L, HA 10 mg/L (pH 4.0 +/- 0.1, 5.0 +/- 0.2, and 6.0 +/- 0.2) and 50 mg/L (pH 6.0 +/- 0.2), respectively. The kinetics of dissociation of 243Am(III) after different equilibration time with humic acid-coated gamma-Al2O3 was also investigated at pH 5.0 +/- 0.2. The experiments were carried out in air and at ambient temperature. The results suggest that the fraction of irreversible bonding of radionuclides to HA-coated Al2O3 increases with increasing pH and is independent of aging time. The assumption of two different 243Am(III)-HA-Al2O3 species, with "fast" and "slow" dissociation kinetics, is required to explain the experimental results. 243Am(III) species present on HA-Al2O3 colloids moves from the "fast" to the "slow" dissociating sites with the increase of aging time.

Actinoid Series Elements↗
PubMed2005

Benchmarking of MCNP for calculating dose rates at an interim storage facility for nuclear waste.

During the operation of research facilities at Research Centre Jülich, Germany, nuclear waste is stored in drums and other vessels in an interim storage building on-site, which has a concrete shielding at the side walls. Owing to the lack of a well-defined source, measured gamma spectra were unfolded to determine the photon flux on the surface of the containers. The dose rate simulation, including the effects of skyshine, using the Monte Carlo transport code MCNP is compared with the measured dosimetric data at some locations in the vicinity of the interim storage building. The MCNP data for direct radiation confirm the data calculated using a point-kernel method. However, a comparison of the modelled dose rates for direct radiation and skyshine with the measured data demonstrate the need for a more precise definition of the source. Both the measured and the modelled dose rates verified the fact that the legal limits (<1 mSv a(-1)) are met in the area outside the perimeter fence of the storage building to which members of the public have access. Using container surface data (gamma spectra) to define the source may be a useful tool for practical calculations and additionally for benchmarking of computer codes if the discussed critical aspects with respect to the source can be addressed adequately.

Benchmarking↗
PubMed2005

Modeling field-scale multiple tracer injection at a low-level waste disposal site in fractured rocks: effect of multiscale heterogeneity and source term uncertainty on conceptual understanding of mass transfer processes.

Multiple factors may affect the scale-up of laboratory multi-tracer injection into structured porous media to the field. Under transient flow conditions and with multiscale heterogeneities in the field, previous attempts to scale-up laboratory experiments have not answered definitely the questions about the governing mechanisms and the spatial extent of the influence of small-scale mass transfer processes such as matrix diffusion. The objective of this research is to investigate the effects of multiscale heterogeneity, mechanistic and site model conceptualization, and source term density effect on elucidating and interpreting tracer movement in the field. Tracer release and monitoring information previously obtained in a field campaign of multiple, conservative tracer injection under natural hydraulic gradients at a low-level waste disposal site in eastern Tennessee, United States, is used for the research. A suite of two-pore-domain, or fracture-matrix, groundwater flow and transport models are calibrated and used to conduct model parameter and prediction uncertainty analyses. These efforts are facilitated by a novel nested Latin-hypercube sampling technique. Our results verify, at field scale, a multiple-pore-domain, multiscale mechanistic conceptual model that was used previously to interpret only laboratory observations. The results also suggest that, integrated over the entire field site, mass flux rates attributable to small-scale mass transfer are comparable to that of field-scale solute transport. The uncertainty analyses show that fracture spacing is the most important model parameter and model prediction uncertainty is relatively higher at the interface between the preferred flow path and its parent bedrock. The comparisons of site conceptual models indicate that the effect of matrix diffusion may be confined to the immediate neighborhood of the preferential flow path. Finally, because the relatively large amount of tracer needed for field studies, it is likely that source term density effect may exaggerate or obscure the effect of matrix diffusion on the movement of tracers from the preferred flow path into the bedrock.

Chemical Phenomena↗
PubMed2001

Cement solidification of simulated off-gas condensates from vitrification of low-level nuclear waste solutions.

Solidification in a cementitious matrix is a viable alternative for low-level nuclear waste management; it is therefore important to understand the behavior and properties of such wasteforms. We have examined the cementitious solidification of simulated off-gas waste streams resulting from the vitrification of low-level nuclear waste. Different possible methods for scrubbing the off-gasses from a vitrifier give rise to three possible types of waste compositions: acidic (from aqueous dissolution of volatile NOx and POx carried over from the vitrifier), basic (from neutralizing the former with sodium hydroxide), and fully carbonated (arising from a direct-combustion vitrifier). Six binder compositions were tested in which ordinary Portland cement was replaced at different proportions by fly ash and/or ground granulated blast furnace slag. A high solution to binder ratio of 1l/1 kg was used to minimize the volume of the wasteform and 10% attapulgite clay was added to all mixes to ensure that the fresh mix did not segregate prior to setting. The 28-day compressive strengths decreased when a high proportion of cement was replaced with fly ash, but were increased significantly when the cement was replaced with slag. The heats of hydration at early age for the various solids compositions decreased when cement was replaced with either fly ash or slag; however, for the fly ash mix the low heat was also associated with a significant decrease in compressive strength. High curing temperature (60 degrees C) or the use of extra-fine slag did not significantly affect the compressive strength. Recommendations for choice of binder formulations and treatment of off-gas condensates are discussed.

Environmental Pollution↗
PubMed2005

Evolution of technetium speciation in reducing grout.

Cementitious waste forms (CWFs) are an important component of the strategy to stabilize nuclear waste resulting from plutonium production by the U. S. Department of Energy. Technetium (99Tc) is an abundant fission product of particular concern in CWFs because of the high solubility and mobility of Tc(VII), pertechnetate (TcO4-), the stable form of technetium in aerobic environments. CWFs can more effectively stabilize 99Tc if they contain additives that chemically reduce mobile TcO4- to immobile Tc(IV) species. The 99Tc leach rate of reducing CWFs that contain Tc(IV) is much lower than that for CWFs that contain TcO4-. Previous X-ray absorption fine structure studies showed that Tc(IV) species were oxidized to TcO4- in reducing grout samples prepared on a laboratory scale. Whether the oxidizer was atmospheric O2 or NO3- in the waste simulant was not determined. In actual CWFs, rapid oxidation of Tc(IV) by NO3- would be of concern, whereas oxidation by atmospheric O2 would be of less concern due to the slow diffusion and reaction of O2 with the reducing CWF. To address this uncertainty, two series of reducing grouts were prepared using TcO4- containing waste simulants with and without NO3-. In the first series of samples, referred to as "permeable samples", the TcO4- was completely reduced using Na2S, and the samples were sealed in cuvettes made of polystyrene, which has a relatively large O2 diffusion coefficient. In these samples, all of the technetium was initially present as a Tc(IV) sulfide compound, TcSx, which was characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. The EXAFS data is consistent with a structure consisting of triangular clusters of Tc(IV) centers linked together through a combination of disulfide and sulfide bridges as in MoS3. From the EXAFS model, the stoichiometry of TcSx is TC3S10, which is presumably the compound generally referred to as "Tc2S7". The TcSX initially present in the permeable samples was steadily oxidized over 4 years. In the second series of samples, called "impermeable samples", the TcO4- was not initially completely reduced, and the groutsamples were sealed in cuvettes made of poly-(methyl methacrylate), which has a small O2 diffusion coefficient. In the impermeable samples, the remaining TcO4- continued to be reduced, presumably by blast furnace slag in the grout, as the samples aged. When the impermeable samples were opened and exposed to atmosphere, the lower-valent technetium species were rapidly oxidized to TcO4-.

Nitrates↗
PubMedDate not supplied

Identifying the potential loss of monitoring wells using an uncertainty analysis.

From the mid-1940s through the 1980s, large volumes of waste water were discharged at the Hanford Site in southeastern Washington State, causing a large-scale rise (>20 m) in the water table. When waste water discharges ceased in 1988, ground water mounds began to dissipate. This caused a large number of wells to go dry and has made it difficult to monitor contaminant plume migration. To identify monitoring wells that will need replacement, a methodology has been developed using a first-order uncertainty analysis with UCODE, a nonlinear parameter estimation code. Using a three-dimensional, finite-element ground water flow code, key parameters were identified by calibrating to historical hydraulic head data. Results from the calibration period were then used to check model predictions by comparing monitoring wells' wet/dry status with field data. This status was analyzed using a methodology that incorporated the 0.3 cumulative probability derived from the confidence and prediction intervals. For comparison, a nonphysically based trend model was also used as a predictor of wells' wet/dry status. Although the numerical model outperformed the trend model, for both models, the central value of the intervals was a better predictor of a wet well status. The prediction interval, however, was more successful at identifying dry wells. Predictions made through the year 2048 indicated that 46% of the wells in the monitoring well network are likely to go dry in areas near the river and where the ground water mound is dissipating.

Environmental Monitoring↗
PubMed1998

Micronucleated erythrocytes frequency and radiocesium bioconcentration in pikes (Esox lucius) caught in the Tom River near the nuclear facilities of the Siberian Chemical Complex (Tomsk-7).

Between 1957 and 1993, the Siberian Chemical Complex (Tomsk-7) located in the Tomsk region (Russia) regularly discharged radioactive liquid wastes into the Tom River which resulted in an extensive contamination of large territories with long lived radionuclides such as cesium-137 and strontium-90. In the summers of 1996 and 1997, Research Team of Siberian Medical University conducted biodosimetry and cytogenetic monitoring of pikes (Esox lucius) caught in the Tom River at various distances downstream from the Siberian Chemical Complex (SCC) using the micronucleus test and the gamma spectroscopy. Our findings demonstrated that the difference in frequency of micronucleated erythrocytes between the radiation-exposed fish caught downstream from the SCC and the controls was statistically significant (P < 0.01). Moreover, we found a good correlation between radiocesium concentration and micronucleated erythrocyte frequency in pikes. It was found that both the micronucleated erythrocyte frequency in pike blood and the level of the pike radiocesium concentration depended on the age of pikes. The micronucleated erythrocyte frequency gradually increased from the 1-year-old pikes to the over 20-year-old pikes. On the other hand, the average level of radiocesium concentration gradually increased from the 1-year-old pikes only up to the 10-year-old pikes. There is no correlation between radiocesium concentration and micronucleated erythrocyte frequency in the over 10-year-old pikes.

Age Factors↗
PubMed2003

Uranium transport around the reactor zone at Bangombé and Okélobondo (Oklo): examples of hydrogeological and geochemical model integration and data evaluation.

The sites at Bangombé and Okélobondo (Oklo) in Gabon provide a unique opportunity to study the behaviour of products from natural nuclear reactions in the vicinity of reactor zones which were active around two billion years ago. The Commission of the European Communities initiated the Oklo Natural Analogue Programme. One of the principal aims was to study indications of present time migration of elements from the reactor zones under ambient conditions. The hydrogeological and hydrochemical data from the Oklo sites were modelled in order to better understand the geochemical behaviour of radionuclides in the natural system, by using independent models and by comparing the modelling outcome. Two modelling approaches were used: M3 code (hydrochemical mixing and mass balance model), developed by the Swedish Nuclear Fuel and Waste Management Company (SKB) and HYTEC (reactive transport model) developed by Ecole des Mines de Paris. Two different reactor zones were studied: Bangombé, a shallow site, the reactor being at 11 m depth, and OK84 at Okélobondo, situated at about 450 m depth, more comparable with a real repository location. This allowed the validation of modelling tools in two different sedimentary environments: one shallow, with a more homogeneous layering situated in an area of meteoric alteration, and the other offering the opportunity to study radionuclide migration from the reaction zone over a distance of 450 m through very heterogeneous sedimentary layers. The modeling results indicate that the chemical reactions retarding radionuclide transport are very different at the two sites. At Bangombé, the decomposition of organic material consumes oxygen and at Okélobondo the oxygen is consumed by inorganic reactions resulting, in both cases, in uranium retardation. Both modelling approaches (statistic with M3 code and deterministic with HYTEC code) could describe this situation. The goal of this exercise is to test codes which can help to describe and understand the processes taking place at the sites, validate the models with in situ data, and thus build confidence in the tools used for future site characterization. Ultimately, this allows identifying and selecting processes and parameters that can be used as input into repository performance assessment calculations and modelling exercises.

Environmental Monitoring↗
PubMed2006

Manufacturing and characterization of Pd nanoparticles formed on immobilized bacterial cells.

AIMS: To fabricate and analyse Pd nanoparticles on immobilized bacterial cells. METHODS AND RESULTS: Biological ceramic composites (biocers) were used as a template to produce Pd(0) nanoparticles. The metal-binding cells of the uranium mining waste pile isolate, Bacillus sphaericus JG-A12 were used as a biological component of the biocers and immobilized by using sol-gel technology. Vegetative cells and surface-layer proteins of this strain are known to bind high amounts of Pd(II) that can be reduced to Pd(0) particles by the addition of a reducing agent. Sorption of Pd(II) by the biocers from a metal complex solution was studied by inductively coupled plasma mass spectroscopy analyses. After embedding into sol-gel ceramics, the cells retained their Pd(II)-binding capability. Pd(0) nanoclusters were produced by the addition of hydrogen as reducing agent after the sorption of Pd(II). The interactions of Pd(0) with the biocers and the formed Pd(0) nanoparticles were investigated by extended X-ray absorption fine structure spectroscopy. The particles had a size of 0.6-0.8 nm. CONCLUSIONS: Bacterial cells that were immobilized by embedding into sol-gel ceramics were used as a template to produce Pd nanoclusters of a size smaller than 1 nm. These particles possess interesting physical and chemical properties. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of embedded bacterial cells as template enabled the fabrication of immobilized Pd(0) nanoparticles. These particles are highly interesting for technical applications, such as the development of novel catalysts.

Bacillus↗
PubMed2006

Adsorption of biometals to monosodium titanate in biological environments.

Monosodium titanate (MST) is an inorganic sorbent/ion exchanger developed for the removal of radionuclides from nuclear wastes. We investigated the ability of MST to bind Cd(II), Hg(II), Au(III), or the Au-organic compound auranofin to establish the utility of MST for applications in environmental decontamination or medical therapy (drug delivery). Adsorption isotherms for MST were determined at pH 7-7.5 in water or phosphate-buffered saline. The extent of metal binding was determined spectroscopically by measuring the concentrations of the metals in solution before and after contact with the MST. Cytotoxic responses to MST were assessed using THP1 monocytes and succinate dehydrogenase activity. Monocytic activation by MST was assessed by TNFalpha secretion (ELISA) with or without lipopolysaccharide (LPS) activation. MST adsorbed Cd(II), Hg(II), and Au(III) under conditions similar to those in physiological systems. MST exhibited the highest affinity for Cd(II) followed by Hg(II) and Au (III). MST (up to 100 mg/L) exhibited only minor (<25% suppression of succinate dehydrogenase) cytotoxicity and did not trigger TNFalpha secretion nor modulate LPS-induced TNFalpha secretion from monocytes. MST exhibits high affinity for biometals with no significant biological liabilities in these introductory studies. MST deserves further scrutiny as a substance with the capacity to decontaminate biological environments or deliver metals or metal compounds for therapeutic applications.

Adsorption↗
PubMed2004

Molecular hydrogen from water radiolysis as an energy source for bacterial growth in a basin containing irradiating waste.

Although being deionized, filtered and therefore normally deeply oligotrophic, the water from a basin containing irradiating waste presented relatively high bacterial concentrations (ca 10(5) cfu ml(-1)) and biofilm development at its surface and on the walls. This water was characterized by a high concentration of molecular H2 due to water radiolysis, while its electrochemical potential was around +400 mV due the presence of dissolved O2 and active oxygen compounds. This combination of H2 availability and of an oxidant environment is completely original and not described in nature. From surface and wall biofilms, we enumerated the autotrophic populations ( approximately 10(5) bacteria ml(-1)) able to grow in presence of H2 as energy source and CO2 as carbon source, and we isolated the most abundant ones among cultivable bacteria. They efficiently grew on a mineral medium, in the presence of H2, O2 and CO2, the presence of the three gases being indispensable. Two strains were selected and identified using their rrs gene sequence as Ralstonia sp. GGLH002 and Burkholderia sp. GGLH005. In pure culture and using isotope exchange between hydrogen and deuterium, we demonstrated that these strains are able to oxidize hydrogen as energy source, using oxygen as an electron acceptor, and to use carbon dioxide as carbon source. These chemoautotroph hydrogen-oxidizing bacteria probably represent the pioneer bacterial populations in this basin and could be primary producers in the bacterial community.

Bacteria↗
PubMed1996

Pilot study of the Urals population by tooth electron paramagnetic resonance dosimetry.

During 1949-1956, about 76 x 10(6)m3 of radioactive liquid waste containing a total activity of 10(17) Bq was discharged into the Techa River by the first Russian industrial nuclear facility Mayak. As a consequence, the population living in the river valley received considerable internal and external radiation doses. The results of a first application of electron paramagnetic resonance (EPR) of tooth enamel for a retrospective individual dose evaluation of the residents of the Techa riverside are presented. Three main contributions to the dose absorbed in tooth enamel have been considered: external exposure mainly from the Techa River sediments, internal exposure mainly due to 90Sr; and background radiation including all other sources of exposure except the Techa River. The teeth of 86 inhabitants of the town Kamensk-Uralskii were analysed to determine the age-dependent contribution of the background radiation to the enamel dose. For 22 residents of the middle and lower Techa riverside, measurements of the 90Sr whole-body content and EPR measurements of the absorbed dose in enamel were used to establish a correlation between these two quantities. Finally, absorbed doses in the enamel of five residents of the upper Techa riverside were determined by EPR method. Contributions of the background radiation and the internal 90Sr contamination were subtracted to determine the external exposure of the residents.

Aged↗
PubMedDate not supplied

Testing and parameterizing a conceptual solute transport model in saturated fractured tuff using sorbing and nonsorbing tracers in cross-hole tracer tests.

Two cross-hole tracer tests involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients (bromide and pentafluorobenzoate) and one weakly sorbing solute tracer (lithium ion) were conducted in two different intervals at the C-wells complex near the site of a potential high-level nuclear waste repository at Yucca Mountain, NV. The tests were conducted to (1) test a conceptual radionuclide transport model for saturated, fractured tuffs near Yucca Mountain and (2) obtain transport parameter estimates for predictive modeling of radionuclide transport. The differences between the responses of the two nonsorbing tracers and the sorbing tracer (when normalized to injection masses) were consistent with a dual-porosity transport system in which matrix diffusion was occurring. The concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggested that diffusion occurred primarily into matrix pores, not simply into stagnant water within the fractures. The K(d) values deduced from the lithium responses were generally larger than K(d) values measured in laboratory batch sorption tests using crushed C-wells cores. This result supports the use of laboratory-derived K(d) values for predicting sorbing species transport at the site, as the laboratory K(d) values would result in underprediction of sorption and hence conservative transport predictions. The tracer tests also provided estimates of effective flow porosity and longitudinal dispersivity at the site. The tests clearly demonstrated the advantages of using multiple tracers of different physical and chemical characteristics to distinguish between alternative conceptual transport models and to obtain transport parameter estimates that are better constrained than can be obtained using only a single tracer or using multiple nonsorbing tracers without a sorbing tracer.

Benzoates↗
PubMed1997

Case-control study of leukaemia among young people near La Hague nuclear reprocessing plant: the environmental hypothesis revisited.

OBJECTIVE: To investigate the association between childhood leukaemia and established risk factors or other factors related to La Hague nuclear waste reprocessing plant. DESIGN: Case-control study. SETTING: Area within a 35 km radius of La Hague, Normandy, France. SUBJECTS: Twenty seven cases of leukaemia diagnosed during the period 1978-93 in people aged under 25 years and 192 controls matched for sex, age, place of birth, and residence at time of diagnosis. MAIN OUTCOME MEASURES: Antenatal and postnatal exposure to x rays and viral infections, occupational exposure of parents (particularly ionising radiation), living conditions, lifestyle of parents and children. RESULTS: Increased trends were found for use of local beaches by mothers and children (P < or = 0.01); relative risks 2.87 (95% confidence intervals 1.05 to 8.72) and 4.49 (1.52 to 15.23) when categories were aggregated in two levels (more or less than once a month). Consumption of local fish and shellfish also showed an increased trend (P 0.01); relative risk 2.66 (0.91 to 9.51) when categories were grouped in two levels (more or less than once a week). A relative risk of 1.18 a year (1.03 to 1.42) was observed for length of residence in a granite-built house or in a granitic area. No association was shown with occupational radiation exposure in parents. CONCLUSIONS: There is some convincing evidence in childhood leukaemia of a causal role for environmental radiation exposure from recreational activities on beaches. New methods for identifying the environmental pathways, focusing on marine ecosystems, are warranted.

Adolescent↗