Radioactive 36Cl Research Articles

Isotopic discrimination of natural and anthropogenic perchlorate sources in groundwater in a semi-arid region of northeastern Oregon (USA)

Perchlorate (ClO4−) has synthetic and natural sources. Synthetic ClO4− is released to the environment from its use as an oxidant in military and aerospace applications, and from its presence in a variety of common commercial products, such as safety flares, chlorate herbicides, and fireworks. Natural sources of ClO4− in the environment include imported nitrate fertilizers derived from salt deposits in the Atacama Desert of Chile and indigenous natural ClO4− that accumulates in unsaturated soils and groundwaters in other arid and semi-arid environments, largely from atmospheric deposition. The stable isotope ratios of chlorine (37Cl/35Cl) and oxygen (18O/16O, 17O/16O) and the isotopic abundance of radioactive 36Cl in ClO4− can be used to discriminate these different sources. Perchlorate was previously detected at relatively high concentrations (3.8–34.7 μg/L) in groundwater from many wells in the Boardman-Umatilla area near the Columbia River in northeastern Oregon, which is a semi-arid, highly agricultural, heavily irrigated area that includes several past and current military installations. Eight representative groundwater wells were sampled throughout this region and isotopic characteristics of ClO4− collected from each well were measured along with other chemical and isotopic parameters including tritium and other groundwater age indicators. Isotopic data indicate that indigenous natural ClO4− was present in groundwater from all sampled wells and was the predominant source in five of the wells. Synthetic ClO4− was present in the three remaining wells with natural ClO4−, and a minor fraction of Atacama-fertilizer-derived ClO4− was indicated in one of the wells. Data from this study expand the geographic area of the USA in which indigenous natural ClO4− has been detected to include the semi-arid northwest. This study also illustrates the role of irrigation recharge as a mechanism for producing relatively high concentrations of indigenous natural ClO4− in groundwater by flushing accumulated salts from the unsaturated zone.

Spark plasma sintering-densified vanadinite apatite-based chlorine waste forms with high thermal stability and chlorine confinement

Effective management of the long-lived radioactive 36Cl is necessary for the development of pyrochemical reprocessing of used fuels and also the molten salt reactors in which a large quantity of Cl-containing waste is encountered. Significant challenge exists in developing advanced waste form matrix with high Cl confinement capability and fabrication technology with minimized loss of Cl. In this work, Cl-bearing vanadinite apatite (Pb5(VO4)3Cl) powder samples are synthesized by solid state reaction at room temperature using high energy ball milling (HEBM), and dense pellets above 99% theoretical density can be consolidated by spark plasma sintering (SPS) at a temperature as low as 450 °C for 3 min. The effects of various sintering temperatures (300–800 °C) on physical density, microstructure, thermal stability and mechanical properties of the SPS densified pellets are investigated. Microstructure analysis shows that the average grain size of nanocrystalline ceramic is less than 190 nm when sintered at 450 °C, and the sintered microstructure is dominated by grain growth at higher sintering temperatures. No phase decomposition and significant chlorine loss can be identified during HEBM and low temperature SPS consolidation processes. Thermal gravimetric analysis (TGA) test indicates that the phase decomposition and chlorine loss occur only at an elevated temperature 830 °C for both HEBM-prepared powders and SPS densified pellets. Vanadinite pellets densified at 450 °C possess the maximum hardness of 4.6 GPa. The SPS-densified Cl-bearing vanadinite apatite displays high confinement of chlorine and a good thermal stability, and thus could be used as a potential nuclear waste form for the immobilization of the long-lived and highly volatile 36Cl.

Uptake of chloride and carbonate ions by calcium monosulfoaluminate hydrate

Decommissioning of old nuclear reactors may produce waste streams containing chlorides and carbonates, including radioactive 36Cl− and 14CO32−. Their insolubilization by calcium monosulfoaluminate hydrate was investigated. Carbonates were readily depleted from the solution, giving at thermodynamic equilibrium monocarboaluminate, monocarboaluminate+calcite, or calcite only, depending on the initial ratio between the anion and calcium monosulfoaluminate hydrate. Chloride ions reacted more slowly and were precipitated as Kuzel's salt, Kuzel's and Friedel's salts, or Friedel's salt only. Rietveld refinement of X-Ray powder diffraction patterns was successfully used to quantify the phase distributions, which were compared to thermodynamic calculations. Moreover, analysing the lattice parameters of Kuzel's salt as a function of its chloride content showed the occurrence of a restricted solid solution towards the sulfate side with general formula 3CaO·Al2O3·xCaCl2·(1−x)CaSO4·(12−2x)·H2O (0.36≤x≤0.50).

同位体・希ガストレーサによる地下水研究の現状と新展開

Environmental tracers become a common tool for the groundwater study and a number of methods have been presented in order to understand groundwater flow processes, water budget, origins, chemical reaction processes and retention time. Tracers often used are selected and reviewed for their various methods and advantages as follows; 1) stable 18O, D in water, 2) stable 13C and radioactive 14C in DIC, 3) noble gases such as He, Ne, Ar, Kr, Xe and their isotopes, 4) radioactive 36Cl in dissolved chloride and some heavier isotopes, and 5) inert gaseous species such as CFCs.If they are less reactive species, they likely preserve information at the time of recharge or their origin. Use of D, 18O and the d-value of water is the powerful tool to determine the recharge area because recharged meteoric water have their inherent isotopic ratios correlated with the recharge elevation, distance from the coast, or the local topography. Carbon-bearing species are more reactive though, use of stable isotopes of DIC leads to identify its origin and helps to analyze the chemical reaction between minerals and water or gas addition processes during the groundwater flow in aquifers. Radioactive 14C has been used to estimate groundwater age however special attention should be paid for, i.e., the origin of DIC, before applying the method. Noble gas tracers are the useful species to presume recharge temperature from their concentrations in water using their temperature dependence of solubilities. Radiogenic 4He concentration can be used for the very long-term groundwater dating since the 4He is produced in the crust and is accumulated in the deep aquifers, if the local accumulation rate of 4He is known. Radioactive 36Cl has been used to determine the age of very old saline waters up to million years. This isotope will also be convenient for the dating of very younger waters, by the use of bomb-produced 36Cl resulted from surface nuclear experiments near the seawater in the 1950s. Chlorofluorocarbons (CFCs) are the gas species produced by the recent human activity and dissolve in water during the recharge, therefore, the affected younger groundwater will have equivalent CFCs concentrations with the atmospheric CFCs concentrations at the time of the recharge. As these species are easy to detect with very high sensitivity, this tracer has now been applied not only for the age determination but for the mixing or contamination of shallow young water to a deep old groundwater. As an individual method listed above is valid only for the very simple flow system, appropriate assumptions or coupling of using different tracers is necessary to understand natural complex groundwater flow system where mixing of groundwaters of different origin or age occurs. Combination of tracers helps us simulating the complex system in detail and is being a growing trend in groundwater study.

Formation, adsorption and separation of high molecular weight disinfection byproducts resulting from chlorination of aquatic humic substances

A significant portion of the unidentified disinfection byproducts (DBPs) in chlorinated drinking water can be attributed to high molecular weight (MW)-chlorinated DBPs (above 500 Da) that may have adverse health effects. In this work, issues on the formation, adsorption and separation of high MW-chlorinated DBPs were investigated by introducing radioactive 36Cl into humic substance samples. The results show that the amount of high MW-chlorinated DBPs during chlorination decreased with the increase of contact time from 1 to 120 h, increased with the increase of pH from 5.5 to 9.5, and was less in the ultrafiltered samples from Suwannee River fulvic acid than from Suwannee River humic acid. The high MW-chlorinated DBPs were found to be effectively adsorbed by activated carbon and be possibly reduced to Cl − by activated carbon, but not to be readily desorbed from the activated carbon. Those high MW-chlorinated DBPs were demonstrated to be incapable of resolution into discrete peaks by any of the three liquid chromatography columns studied. The significant implications of these results are discussed.

36Cl in modern groundwater dated by a multi-tracer approach ( 3H/ 3He, SF 6, CFC-12 and 85Kr): a case study in quaternary sand aquifers in the Odense Pilot River Basin, Denmark

36Cl produced by thermonuclear bomb testing has been proposed as an additional tool to date or at least to identify recent groundwater components. In order to investigate the behaviour of 36Cl in shallow groundwater a multi-tracer approach ( 3H/ 3He, SF 6, CFC-12 and 85Kr) was used to characterise and date the groundwater of a quaternary sands aquifer which is located on the Island of Funen near the city of Odense, Denmark. Recharge to the semi-confined shallow aquifer occurs through permeable sand windows and fractured tills at the surface. Locally, however, mixing with older pre-bomb water from the underlying limestone aquifer may occur. The integrated analyses of the available tracer data allowed a well constrained age structure determination of the investigated water system. The 36Cl/Cl ratios measured in groundwater were used to reconstruct the fallout rates for radioactive 36Cl at Odense. The calculated fallout values exceeded the fallout estimated based on data from the Dye-3 ice core in Greenland. Recycling of the bomb peak fallout seems to be the most probable reason of the high values measured. The local extent of this process is difficult to quantify, which impedes the use of 36Cl for dating.

Characterization of high molecular weight disinfection byproducts resulting from chlorination of aquatic humic substances.

Aquatic humic substances react with chlorine to produce numerous disinfection byproducts (DBPs) during chlorination of drinking water. Although low molecular weight (MW) chlorinated DBPs have been intensively studied over the past several decades, relatively little is known about high MW chlorinated DBPs (above 500 Da) that may be associated with adverse health implications. In this work, carrier-free radioactive 36Cl was introduced into a Suwannee River fulvic acid sample to label the chlorine-containing DBPs. By combining the fractionation techniques of ultrafiltration (UF) and size exclusion chromatography (SEC) with the detection of 36Cl, UV, and dissolved organic carbon (DOC), the high MW region in the SEC-36Cl profiles of the chlorinated sample with and without UF was defined. SEC-UV and SEC-DOC profiles were found to be approximately indicative of SEC-36Cl profiles for the high MW region. The MW distribution shows that the high MW chlorinated DBPs were highly dispersed with an average MW around 2000 Da based on calibration with polystyrene sulfonate standards. The Cl/C atomic ratios of the high MW DBPs were roughly constant (0.025), which is much lower than those of the common known chlorinated DBPs.

In vivo incorporation of radioactive 36Cl, a method for monitoring chloro compounds in biological material

A new method for fast and easy monitoring of the presence, isolation, and separation of natural chloro compounds in plants is described. The method relies on the in vivo incorporation of radioactive 36Cl and new enhancement methods in autoradiographic technology. The method allows the time of exposure to be limited to 4 days and is thus suitable for routine purposes.

The Cosmic-Ray Radioactive Nuclide [TSUP]36[/TSUP]C[CLC]l[/CLC] and Its Propagation in the Galaxy

Radioactive 36Cl has been resolved from 35Cl and 37Cl for the first time in the cosmic radiation with measurements obtained from the high-resolution High-Energy Telescope (HET) carried on the NASA-ESA Ulysses spacecraft. Within the framework of a homogeneous propagation model wherein all 36Cl is of spallation origin, the average density of the interstellar gas ρ, through which all cosmic-ray nuclei propagate, was determined. Heliospheric modulation was included in the analysis. The abundance ratio 36Cl/Cl=5.2 ± 1.8% at an average energy of 238 MeV u-1 yields ρ=0.28+ 0.12−0.10 atoms cm-3. Although 36Cl has a relatively short half-life (τ½=3.01 × 105 yr) compared with the approximately 20 Myr confinement or escape time Tesc for cosmic rays in the Galaxy derived from 10Be or 26Al analysis, it is shown that the confinement time based on 36Cl analysis is 18+ 10−6 Myr. Radioactive 10Be,26Al, and 36Cl are all produced by nuclear interactions during propagation from Galactic sources to the observer. However,10Be,26Al, and 36Cl are each predominantly products of different primary cosmic-ray nuclei.54Mn is the fourth radioactive isotope measured by the Ulysses HET. Unfortunately, its decay half-life to 54Fe is difficult to determine. Recent measurements yielded τ½=6.3 × 105 yr, leading to ρ=0.40+ 0.23−0.15 atoms cm-3 with a confinement time Tesc=11 Myr.

Interaction of chloride with yeast aminopeptidase I. Equilibrium binding studies.

The effect of chloride on metal binding by yeast aminopeptidase I, as well as the binding of chloride to various enzyme forms were studied by means of a micro-centrifugation technique using radioactive 36Cl- as a ligand. Chloride did not significantly alter the binding of activating Zn2+, or binding of Co2+ to the essential metal sites. Both the native Zn2+ enzyme and Co2+-substituted aminopeptidase I bind stoichiometric amounts of C1- (1 Cl-/subunit) with apparent dissociation constants of 0.1-0.2 mM. Additional Cl- was bound at higher concentrations. In contrast to the metal-containing enzyme forms the apoenzyme did not express the high-affinity chloride binding site.

Cl − fluxes across isolated, perfused gills of the chinese crab Eriocheir sinensis (M.Edw.) acclimated to fresh water

1. 1. The movements of Cl −1 have been studied in the so-called anterior and posterior gills of E. sinensis using radioactive 36Cl −1. 2. 2. The anterior gills hardly show any significant movements of Cl −1. They thus have a very low (if any) permeability to that ion. On the contrary, the posterior gills show both passive fluxes and an active inward movement of Cl −1. 3. 3. The Cl −1 influx in the posterior gills is largely sensitive to the amount of K + in the perfusion saline.

36C1 in a halite layer from the bottom of the Dead Sea

Stable and radiogenic isotope compositions are commonly used to identify the solution from which minerals such as sulphate, carbonate and silicate were crystallized. Both the sources and the ages of evaporite deposits can be determined by measuring radioactive 36Cl concentrations using new developments in accelerator mass spectrometry. Halite crystals found in saline sediments, which could not be measured by isotope techniques until this method was developed, are usually assumed to have precipitated from the lake water during former dry periods. In the case of the Dead Sea we tested this assumption by comparing the abundance of 36Cl isotopes in a shallowly buried halite layer with that in the overlying water. We found that the 36Cl/Cl ratio is significantly lower in the halite, which indicates that the salt did not crystallize from this water but from a solution originating from the Tertiary diapir underneath the sea or that the salt represents the top of the Mt Sdom formation diapir.

Use of Radioactive 36Cl to Determine Distribution of Chloride in Poultry Meat Exposed to Chlorinated Chillwater

Chlorine has been used to control microbial levels in poultry chillwater systems for many years. Recendy, however, concern has arisen regarding the fate of organic compounds when exposed to chlorinated water supplies. The present study was designed to determine the distribution and nature of chloride in poultry tissues exposed to chillwater containing radioactive 36Cl. Breasts from freshly slaughtered chickens were chilled for 3 min., 1 hr., or 24 hr. in water containing 50 p.p.m. of chlorine. Raw and cooked portions of skin and muscle were then assayed for radioactivity. Skin portions consistendy contained higher levels of radioactivity than muscle. For example, skin exposed to chlorinated chillwater for 1 hr. contained 21.8 p.p.m., whereas muscle tissues contained 4.4 p.p.m. The concentration of 36Cl in tissues increased as exposure time to the chlorinated chillwater increased. Cooking chlorinated tissues generally reduced the concentration of chloride in skin and increased the concentration in muscle. Tests conducted to define the nature of “added” chloride in the tissue indicate that it is probably present as an inorganic salt and not as organochlorine compounds.