Novel methodology for the study of mercury methylation and reduction in sediments and water using <Superscript>197</Superscript>Hg radiotracer

Mercury tracers are powerful tools that can be used to study mercury transformations in environmental systems, particularly mercury methylation, demethylation and reduction in sediments and water. However, mercury transformation studies using tracers can be subject to error, especially when used to assess methylation potential. The organic mercury extracted can be as low as 0.01% of the endogenous labeled mercury, and artefacts and contamination present during methylmercury (MeHg) extraction processes can cause interference. Solvent extraction methods based on the use of either KBr/H₂SO₄ or HCl were evaluated in freshwater sediments using ¹⁹⁷Hg radiotracer. Values obtained for the ¹⁹⁷Hg tracer in the organic phase were up to 25-fold higher when HCl was used, which is due to the coextraction of ¹⁹⁷Hg²⁺ into the organic phase during MeHg extraction. Evaluations of the production of MeHg gave similar results with both MeHg extraction procedures, but due to the higher Hg²⁺ contamination of the controls, the uncertainty in the determination was higher when HCl was used. The Hg²⁺ contamination of controls in the HCl extraction method showed a nonlinear correlation with the humic acid content of sediment pore water. Therefore, use of the KBr/H₂SO₄ method is recommended, since it is free from these interferences. ¹⁹⁷Hg radiotracer (T _1/2 = 2.673 d) has a production rate that is about 50 times higher than that of ²⁰³Hg (T _1/2 = 46.595 d), the most frequently used mercury radiotracer. Hence it is possible to obtain a similar level of performance to ²⁰³Hg when it is used it in short-term experiments and produced by the irradiation of ¹⁹⁶Hg with thermal neutrons, using mercury targets with the natural isotopic composition. However, if the 0.15% natural abundance of the ¹⁹⁶Hg isotope is increased, the specific activity of the ¹⁹⁷Hg tracer can be significantly improved. In the present work, ¹⁹⁷Hg tracer was produced from mercury 51.58% enriched in the ¹⁹⁶Hg isotope, and a 340-fold increase in specific activity with respect to natural mercury targets was obtained. When this high specific activity tracer is employed, mercury methylation and reduction experiments with minimum mercury additions are feasible. Tracer recovery in methylation experiments (associated with Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike, but also with Hg²⁺ contamination and Me¹⁹⁷Hg artefacts) with marine sediments was about 0.005% g⁻¹ WS (WS: wet sediment) after 20 h incubation with mercury additions of 0.05 ng g⁻¹ WS, which is far below natural mercury levels. In this case, the amount of Hg²⁺ reduced to Hg⁰ (expressed as the percent ¹⁹⁷Hg⁰ recovered with respect to the ¹⁹⁷Hg²⁺ added) varied from 0.13 to 1.6% g⁻¹ WS. Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike after 20 h of incubation of freshwater sediment ranged from 0.02 to 0.13% g⁻¹ WS with mercury additions of 2.5 ng g⁻¹ WS, which is also far below natural levels. ¹⁹⁷Hg⁰ recoveries were low, 0.0058 ± 0.0013% g⁻¹ WS, but showed good reproducibility in five replicates. Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spiked in freshwater samples ranged from 0.1 to 0.3% over a period of three days with mercury additions of 10 ng L⁻¹. A detection limit of 0.05% for Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike was obtained in seawater in a 25 h incubation experiment with mercury additions of 12 ng L⁻¹.     

Evaluation of <Superscript>137</Superscript>Cs soil-to-plant transfer: Natural and model experiments

Soil and meadow grass were sampled in the whole territory of Lithuania in 1992–2000. For the laboratory experiment, spring wheat Triticum aestivum L. “Nandu” was used because its root system type is similar to that of perennial meadow grass. The ¹³⁷Cs soil-to-plant transfer factor of spring wheat was determined and the results were compared with the predicted values using a compartment model of soil-to-plant transfer and with the results of the field experiment. The results of comparing the measured and calculated transfer factor using the model show rather good coincidence, however, the calculated values were overestimated. The reason for overestimation can be that the uptake rate is not influenced only by the soil-to-plant transfer. The results of the model experiment (from 0.005 m²·kg⁻¹ to 0.053 m²·kg⁻¹) are close to those of the field measurements for grass (from 0.013 m²·kg⁻¹ in 1992–1995 to 0.10 m²·kg⁻¹ in 1999–2000).     

Determination of <Superscript>237</Superscript>Np, <Superscript>93</Superscript>Zr and other long-lived radionuclides in medium and low level radioactive waste samples

The majority of long-lived radionuclides produced in the nuclear fuel cycle can be regarded as “difficult-to-measure” nuclides, hence chemical separation is needed before the nuclear measurement of them. A combined radiochemical procedure that enables the simultaneous determination of some “difficult-to-measure” nuclides in medium and low level radioactive wastes has been developed in our laboratory. Recently, this method has been extended for determination of ²³⁷Np and ⁹³Zr. ²³⁷Np and ⁹³Zr are pre-concentrated by co-precipitation on iron(II) hydroxide and zirconium oxide, separated by extraction chromatography using UTEVA, and measured by inductively coupled plasma mass spectrometry (ICP-MS). As even traces of polyatomic ions and isotopes at m/z 237 or 93 cause considerable interferences during ICP-MS detection, a purification step by extraction chromatography was needed. Analyzing real samples (evaporation concentrates of a nuclear power plant) 66–99% and 31–99% chemical yields were achieved for Np and Zr, respectively.     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Clean conditions for the determination of ultra-low levels of mercury in ice and snow samples

Laboratory facilities and methods are presented for the determination of ultra-low levels of mercury (Hg) in ice and snow samples originating from polar ice caps or temperate regions. Special emphasis will be given to the presentation of the clean laboratory and the cleaning procedures. The laboratory is pressurized with air filtered through high efficiency particle filters. This first filtration is not enough to get rid of contamination by Hg in air. Experiments are conducted in a clean bench, especially built for Hg analysis, equipped with both particle filter and activated charcoal filter. It allows to obtain very low levels of atmospheric Hg contamination. Ultrapure water is produced for cleaning all the plastic containers that will be used for ice and snow samples and also for the dilution of the standards. Hg content in laboratory water is about ¶0.08 ± 0.02 pg/g. A Teflon system has been developed for the determination of Hg in ice and snow samples based on Hg(II) reduction to Hg(0) with a SnCl₂/HNO₃ solution followed by the measurement of gaseous Hg(0) with a Hg analyzer GARDIS 1A+ based on the Cold Vapor Atomic Absorption Spectroscopy method. Blank determination is discussed.     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations. Received: 24 September 1996 / Revised: 14 January 1997 / Accepted: 18 January 1997     

Design and Performance of a Compact Li<Superscript>+</Superscript> Ion Attachment Mass Spectrometry System with an Atmospheric Sampling Device

This report describes the development of a compact ion attachment mass spectrometry system. A single turbomolecular pump was employed to fill the basic requirements for vacuum conditions simply and cost-effectively, without the need for a differential pumping stage. A Li⁺ ion source was placed in the first of two vacuum chambers; a 0.4 mm aperture allowed the product ions to enter the second chamber for mass analysis. With the present system, any chemical species, including radical intermediates, can be detected at atmospheric pressure in real-time. The minimum detectable amount (at S/N = 3) of toluene was around 1.3 × 10^–12 g/s with a linearity greater than 10⁴. For illustrative purposes, we tested the system on laboratory air and on aroma compounds in the headspace of the Yuzu plant, Citrus junos.     

Comparison of strategies to quantify uncertainty of lead measurements in biological tissue at mg kg<Superscript>–1</Superscript> level

The expression of measurement uncertainty in analytical chemistry still presents some difficulties. According to the various guides and standards, several approaches are possible. This paper present two referenced approaches applied to the determination of Pb in a biological tissue at the mg kg^–1 level. Estimations were achieved, either from inter-laboratory precision data, or from the uncertainty propagation equation applied to the measurements of a single laboratory. When comparing final values, for an average concentration of about 2.0 mg kg^–1, expanded uncertainties range from ±0.05 mg kg^–1 up to ±0.31 mg kg^–1, i.e. by a factor of 6. Obviously, both approaches of estimating uncertainty do not cover the same sources of uncertainty and it is interesting to try to understand better these discrepancies in order to try to define realistic guidelines for analysts. Moreover the experimental results of the study are given where a wide number of techniques is applied. Received: 5 May 2002 Accepted: 17 June 2002 Correspondence to M. Feinberg     

Clean conditions for the determination of ultra-low levels of mercury in ice and snow samples

Laboratory facilities and methods are presented for the determination of ultra-low levels of mercury (Hg) in ice and snow samples originating from polar ice caps or temperate regions. Special emphasis will be given to the presentation of the clean laboratory and the cleaning procedures. The laboratory is pressurized with air filtered through high efficiency particle filters. This first filtration is not enough to get rid of contamination by Hg in air. Experiments are conducted in a clean bench, especially built for Hg analysis, equipped with both particle filter and activated charcoal filter. It allows to obtain very low levels of atmospheric Hg contamination. Ultrapure water is produced for cleaning all the plastic containers that will be used for ice and snow samples and also for the dilution of the standards. Hg content in laboratory water is about 0.08+/-0.02 pg/g. A Teflon system has been developed for the determination of Hg in ice and snow samples based on Hg(II) reduction to Hg(0) with a SnCl2/HNO3 solution followed by the measurement of gaseous Hg(0) with a Hg analyzer GARDIS 1A+ based on the Cold Vapor Atomic Absorption Spectroscopy method. Blank determination is discussed.     

A description of an automatic continuous equilibrium system for the measurement of dissolved gaseous mercury

A novel continuous equilibrium system with high time resolution, i.e. every ten minutes, was developed to sample and determine dissolved gaseous mercury (DGM) in natural surface waters. The system is based on the opposite flow principle, can be connected to a ship’s bow water system, and can be applied under most ambient conditions, such as high wind speeds and onboard a moving ship. For the DGM determination the system uses the measured equilibrium concentration of mercury established between the aqueous and gaseous phases, i.e. DGM = Hg_extr / k _H′, where Hg_extr is the measured mercury concentration in the outgoing gas phase and k_H′ is the dimensionless Henry’s Law constant at the desired temperature and salinity. The efficiency of the system was investigated via theoretical calculations and by comparing the continuous equilibrium system with discrete samples. The measurements obtained by the continuous equilibrium system agree within 13% at the 95% confidence level with the measurements of discrete samples obtained by the traditional technique. The theoretical calculations estimated that the continuous equilibrium system described here had an efficiency of 99% for determining the DGM concentration.     

Potential and Limitations of 2D <Superscript>1</Superscript>H–<Superscript>1</Superscript>H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Summary.  A brief overview of our recent results concerning the application of 2D CRAMPS experiments to investigate a wide range of materials is presented. The abilities of the 2D ¹H–¹H spin-exchange technique to characterize the structure of organic solids as well as the limitations resulting from segmental mobility and from undesired coherence transfer are discussed. Basic principles of ¹H NMR line-narrowing and procedures for analysis of the spin-exchange process are introduced. We focused to the qualitative and quantitative analysis of complex spin-exchange process leading to the determination of domain sizes and morphology in heterogeneous multicomponent systems as well as the characterization of clustering of surface hydroxyl groups in polysiloxane networks. Particular attention is devoted to the determination of the ¹H–¹H interatomic distances in the presence of local molecular motion. Finally we discuss limitations of the ¹³C–¹³C correlation mediated by ¹H–¹H spin exchange to obtain structural constraints. The application of Lee-Goldburg cross-polarization to suppress undesired coherence transfer is proposed. Corresponding author. E-mail: brus@imc.cas.cz Received May 28, 2002; accepted (revised) July 1, 2002     

Distribution of <Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K, <Superscript>232</Superscript>Th and <Superscript>238</Superscript>U in coastal marine sediments of Margarita Island,Venezuela

This work presents the results of ¹³⁷Cs, ⁴⁰K, ²³²Th and ²³⁸U concentration (Bq kg⁻¹) values in coastal marine sediments collected from 38 sites along the coastline of the island of Margarita, Venezuela. The purpose was to determine baseline values for these radionuclides in surface marine sediments and to detect if there were any anomalously high concentration values. Only three of the 38 sediments analyzed had measurable values above the detection limit of 0.9 Bq kg⁻¹ for ¹³⁷Cs and the highest only being 1.4 Bq kg⁻¹. While, the concentration (Bq kg⁻¹) ranges for the primordial radionuclides, ⁴⁰K, ²³²Th and ²³⁸U were as follows: 12.2–211.7, <1.5–9.8 and <4.4–20.7, respectively. These concentration ranges for the primordial radionuclides can be considered as baseline values for surface marine sediments for areas that are considered not polluted by man or contaminated by nature. Finally, the concentration range of ¹³⁷Cs can also be employed as baseline values, which only seem to have been the result of the atmospheric testing of nuclear weapons in the past.     

The apparent change of activity with temperature in a <Superscript>226</Superscript>Ra decay chain

Radioactive decay rates are to a large extent believed to be independent of the chemical environment. This is the physics basis implicitly assumed in applications such as radioisotope dating. While this statement is a good approximation for most radioactive decays, there are cases where a slight variation of 0.5% or more can be observed, as in the electron capture type of decay. There are renewed interests in possible decay-rate changes with external parameters such as temperature, with controversy as to the phenomenon’s authenticity. In this paper, we study the variation of radioactivity counts that significantly change (up to 50% or more) with temperature. We carefully studied the characteristics of the change and found that the presence of a gaseous decay daughter can pose a serious challenge to a bona fide account of the intrinsic nuclear decay rate. After a careful solution to rate equations of the relevant isotopes under our experimental conditions, we found that most of the radioactivity change could be accounted for by the diffusion and loss of gaseous daughters under the heat, without a supposed change in the intrinsic nuclear decay rate. We hence demonstrate that an accurate determination of the decay constant has to consider the possible diffusion of volatile components in the decay chain. This is especially important in cases involving significant temperature change.     

Evaluation and applications of a gaseous mercuric chloride source

In this study, a diffusion-type device for generating gaseous mercuric chloride (HgCl₂) was systematically evaluated and applied to validate the annular denuder method for sampling gaseous HgCl₂ species in a synthetic gas stream. The results show that it takes at least 48 h for the system to reach a steady-state condition after the diffusion cell reaches the temperature set-point and the carrier gas is activated. The primary Hg species from the source was proven to be HgCl₂. In the temperature range from –5.00 to 11.80 °C, the Hg emission rates from the source vary from 1.8 to 14.2 pg min^–1. It is shown that, under the experimental conditions examined, KCl-coated annular quartz denuders designed for ambient reactive gaseous mercury (RGM) collection could quantitatively collect HgCl₂. It is also demonstrated that the impactors used to remove coarse airborne particulate matter could lead to a loss of up to one third of the HgCl₂ in the gas stream.     

Vertical inventories and fluxes of <Superscript>210</Superscript>Pb, <Superscript>228</Superscript>Ra and <Superscript>226</Superscript>Ra at southern South China Sea and Malacca Straits

Inventories and fluxes of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were determined in sediment cores collected at nine stations covering of the southern South China Sea and Malacca Straits with the thickness of water column between 42 and 83 m depth. The inventories of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were calculated range from 0.15–2.55 Bq cm⁻², 0.05–0.40 Bq cm⁻² and 6.83–83.63 Bq cm⁻², meanwhile the fluxes ranged from 0.005–0.079 Bq cm⁻² yr⁻¹, 0.009–0.048 Bq cm⁻² yr⁻¹ and 0.003–0.037 Bq cm⁻² yr⁻¹, respectively. The results show that the highest inventories and fluxes for ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra were found at station WC 01 and EC 05. Because there are additional sources of ²¹⁰Pb, ²²⁸Ra and ²²⁶Ra, where water transport will brings more dissolved isotopes, influence of the transportation and deposition of suspended particles, fast rate of regeneration and greater production of those radionuclides and others.     

Polymer-coated magnetic nanoparticles for rapid bioassay of <Superscript>90</Superscript>Sr in human urine samples

A rapid bioassay for ⁹⁰Sr was developed involving preconcentration of ⁹⁰Sr/⁹⁰Y from human urine samples with a cation exchange polymer (poly–acrylamido–methyl–propanesulfonic acid) coated onto magnetic nanoparticles, followed by selective elution of ⁹⁰Sr (over ⁹⁰Y) with phosphate for determination by liquid scintillation analysis. The minimum detectable activity for this method (4.9 ± 0.5 Bq/L) is lower than the required sensitivity of 19 Bq/L for ⁹⁰Sr in human urine samples, as defined in the requirements for radiation emergency bioassay techniques for the public and first responders based on the dose threshold for possible medical attention recommended by the International Commission on Radiological Protection. The relative bias was 9.2%, the relative precision was 3.2%, and the linear dynamic range covered 12–600 Bq/L. This simple and rapid bioassay method is found to be in compliance with the HPS ANSI N13.30 performance criteria for radiobioassay.     

Technology of DTPA and immunoglobulins conjugation and their attachment to <Superscript>90</Superscript>Y and <Superscript>177</Superscript>Lu radionuclides

The aim of the study of labeling of ligand–antibody conjugates was to find optimal conditions of preparing of these conjugates and appropriate radioactivity of selected nuclide for applications in nuclear medicine. Conjugation of the γ-immunoglobulin G (human or bovine IgG, polyclonal antibodies) and bifunctional chelating agent, diethylenetriaminepentaacetic acid dianhydride (cDTPAA), was carried out. Various values of the cDTPAA/antibody ratio, the weight concentration of polyclonal or monoclonal antibodies (MEM-97) and buffers were used. Further, the labeling conditions of the DTPA–IgG conjugate by radionuclides ⁹⁰Y and ¹⁷⁷Lu were optimized, and the labeling yield and the conjugation ratio of prepared radionuclide–DTPA–IgG conjugates was determined. Optimal incubation time of the immunoglobulin conjugation was obtained at 30 min from mixing of individual components. The labeling yield of radionuclide–DTPA–antibody conjugate higher than 95% was achieved. Higher values of conjugation ratio of radionuclide–DTPA–antibody conjugate were achieved in 0.1 mol L⁻¹ carbonate buffer, pH 8.5, and the 0.1 mol L⁻¹ carbonate buffer is suitable for studied conjugation systems. This study showed that the labeling yield as well as the conjugation ratio of tested systems depend on the amount of antibody substance, bifunctional chelating agent/antibody molar ratio and pH value of the buffer used.     

Sorption of Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> by Natural Biomaterial: Duck Feather

Feather fibers were modified by treatment with 5% tannic acid (TA) solution. Kinetics of the modification was investigated as a function of the reaction time. The maximum loading of TA on feather reached 8.3% after being treated by TA for 9 h. The adsorption of metal cations (Cu²⁺, Zn²⁺) by unmodified and TA-modified feather fibers was investigated as a function of fiber weight gain, temperature, and pH of the metal solution. The adsorption was enhanced at alkaline pH and ambient temperature and increased with the weight gain of TA. The maximum uptake of metal cations (Cu²⁺, 0.77 mmol/g; Zn²⁺, 0.95 mmol/g) was obtained by TA-modified feather at weight gain: 8.3%, pH 11, while at the acidic pH, the adsorption of metal cations by either unmodified or TA-modified feather was negligible. The influence of anions on the adsorption of metal cations was also studied. The uptake of Cu²⁺ from chloride was higher and faster than that from nitrate. Desorption of the metals was performed at acidic pH 2.5 for 48 h. The feather–TA–metal complexes exhibited higher stability for metal cations than the feather–metal complexes. All these experiments reveal that TA-modified feather fibers have good adsorption to metal cations and can be used as metal adsorbent in wastewater treatment.     

Hydridosilazanes hydrolysis-condensation reactions studied by <Superscript>1</Superscript>H and <Superscript>29</Superscript>Si liquid NMR spectroscopy

Hydridosilazane compounds containing Si–N and Si–H bonds can be used as precursors of SiO_x materials. The hydrolysis-condensation reactions of tetramethyldisilazane, as a polyhydridosilazane model compound, were investigated by ¹H and ²⁹Si liquid NMR spectroscopy. These reactions were carried out at room temperature for up to 120 min in presence of water. The identified products are short linear siloxane species (hydride terminated polydimethylsiloxanes M^HD_xM^H) and cyclosiloxanes. Silicon hydride persistence in the reactional mixture suggested that silazane group is more sensitive to hydrolysis reaction than silicon hydride group. Moreover, additional experiments evidenced that the low steric hindrance of the silicon hydride influences the silazane hydrolysis kinetic. Hence the presence of ammonia released during silazane hydrolysis reaction was demonstrated to be a catalyst of the silicon hydride hydrolysis reaction.