Radiostrontium determination by combination of automated Sr isolation and "on-column" Cherenkov detection using chromatographic model.

A novel analytical solution of non-linear chromatography in case of parabolic isotherm for frontal analysis was obtained by combination of Cole-Hopf and Laplace transform. It was used for simulation of strontium capturing on chromatographic column with aim to improve quantitative determination of low-level 90Sr activities. From the experimentally determined breakthrough curves, the retention factor and the number of theoretical plates were calculated using the Glueckauf and Wenzel relations and by fitting the breakthrough curves for the linear isotherm using MatLab. These were used to simulate the breakthrough curves using a parabolic isotherm solution where the non-linear term of the isotherm was taken as a small negative deviation of the retention factor. On the base of theoretical prediction and experimental data, procedure for automated capturing of strontium on chromatographic column with specific dimension and off line "on-column" Cherenkov detection on commercial ultra low-level liquid scintillation counter was developed. It was shown that analytical solution for parabolic isotherm in comparison with solution for linear isotherm gives better prediction of mass of captured Sr on column filled with small amount of Sr resin and SuperLig®620 in case of elevated Sr concentration, even when non-linear effect is not obvious. The solution also makes it possible to predict the mass of resin required for strontium isolation at 100% yield under given conditions. Considering the limited dimensions of the column, and consequently small mass of the resin in them, it resulted in the low efficiency of the columns, which, however, did not affect the yield in real conditions of isolation. The results have shown that the yields achieved after isolation on SuperLig®620 from real samples are 100%. In addition, it is shown that captured 90Sr can be detected through 90Y ingrowth, on column filled with strontium specific resin, with Cherenkov detection efficiency of at least 50%. The efficiency may be enhanced to 60%, depending on parameters which can affect detection efficiency change (type of column, resin type, surrounding solution, etc.). The developed procedures enable quantitative determination of 90Sr in natural water samples with MDAC below 12 mBq l-1 and solid (soil and vegetation) samples with MDAC below 6 Bq kg-1 within 2-3 days. The proposed solution may easily be implemented in radiochemical laboratories where this type of analysis is routinely done within environmental monitoring or other purposes.

Novel approach for strontium preconcentration from seawater and rapid determination of 89,90Sr in emergency situations.

A novel approach for rapid 89,90Sr determination in seawater samples is developed. For the first time in the radioanalytical application, the features of the synthetic zeolite Z4A and a highly selective material for Sr separation were synergically employed. Seawater composition significantly reduces Sr yield on highly selective solid-phase extraction materials, making the preconcentration step essentially important but laborious and time-consuming. To address this issue, the ability of zeolite 4A to concentrate the Sr from the seawater matrix was employed. With the proposed method, two important goals were achieved: (i) simple preconcentration of Sr that can be conducted directly at the sampling site, enabling a rapid procedure for 89,90Sr determination in emergencies, and (ii) high and stable Sr recoveries (89 ± 4%) necessary for lowering detection limits. Strontium is effectively separated from 1 L of seawater in less than 1.5 h, which is especially important in emergency situations, such as the Fukushima Daiichi Nuclear Power Plant accident. Minimum detectable activities achieved for 89Sr:90Sr activity ratio ∼10:1 were 0.74 Bq/L for 89Sr, and 1.47 Bq/L for 90Sr, detected by Cherenkov counting, 36-38 h after separation, and 30 min counting time.

Synergy of flow injection system and molecular recognition technology products for rapid determination of 89,90Sr and 210Pb.

A rapid, automated separation procedure was developed for radioactive strontium and lead isotope determination. This system includes a portable automated system for the preconcentration and sequential elution of targeting isotopes with an Na2H2EDTA solution from solid phase extraction materials, AnaLig®Sr-01 and SuperLig®620, provided by IBC Technologies. Strontium and lead were separated from the majority of matrix constituents to obtain pure fractions of Pb and Sr prior to radiometric detection. In case of barium presence, it can also be fully isolated and completely separated from Sr. The automated procedure can be successfully used for preconcentration and separation from high as well as low radioactivity samples. With only a 1 mL column filled with SuperLig®620, it is possible to isolate Sr and Pb with 100% recovery from 1 L to 2 L of sample at a flow rate of up to 10 mL min-1 within several hours. 89,90Sr isotopes can be further determined by Cherenkov counting, while 210Pb isotopes can be determined by either gamma spectrometry or liquid scintillation counter. The method was tested and validated using certified standard materials and proficiency test samples. The synergy of automated separation and detection procedures enables the determination of the low level activity of 90Sr and 210Pb in a short time with detection limits of 20 mBq L-1 for both isotopes. The proposed method enables lower labour costs, minimal size of apparatuses and columns, low separation time, and reduced secondary waste production. The automated procedure may be easily implemented in laboratories worldwide and can also be used at sampling sites.

Anthropogenic mercury contamination in sediments of Krka River estuary (Croatia).

Coastal and estuarine sediments play an important role in the biogeochemical cycle of mercury (Hg) in the aquatic environment. When contaminated, sediments can act as a potential source of Hg and may pose a long-term risk to aquatic biota. The aim of this research was to assess spatial and historical distribution of Hg in the sediments of the Krka River estuary, an environment that so far has been regarded as relatively unpolluted. To achieve this goal, 40 surface sediment samples and 7 sediment cores were collected along the entire estuary. Hg concentrations in the surface and deep sediments of the Krka River estuary were found in a broad range 0.042-57.8 mg kg-1, demonstrating significant spatial and temporal differences in Hg input to the estuarine sediments. Two distinct areas were distinguished; upper estuary where the Hg content was comparable to other unpolluted Adriatic sediments, and the lower estuary where sediment profiles reflected the history of anthropogenic Hg input associated with the city of Sibenik. The vertical Hg profile from the most affected area of the estuary, combined with 210Pb and 137Cs dating, demonstrated that a significant increase of Hg input started in late 1940s/early 1950s, mainly related to shipyard activities. This study provided more insight on the Hg concentration in the Krka River estuary, demonstrating that the high values obtained, although localized, were comparable to the ones found in some of the most contaminated sites in the Mediterranean.

Comparison of different methodologies for the 90Sr determination in environmental samples.

The paper describes different isolation/separation and detection procedures for 90Sr determination in the environmental samples which are routinely used in Laboratories A and B. In this context, four different methods for strontium isolation and two methods for detection were tested and compared by 90Sr determination in proficiency test samples (water, soil, vegetation) and animal bone samples. The chromatographic isolation of Sr on Sr resin, AnaLig®Sr01 resin gel, strong base anion exchange resins in nitrate form and combination of strong base anion exchange and Sr resin were used for the examination of the impact of sample matrix constituents on efficiency of strontium isolation (chemical yield), while Cherenkov counting of 90Y and counting of 90Sr(90Y) on proportional counter were used for the quantitative 90Sr determination. The chemical yields obtained with different isolation methods were compared with the emphasis on its influence on reliability of the 90Sr determination in different kinds of samples. The results show that the efficiency of strontium isolation depends on type of sample and separation methodology. The strontium yield on Sr resin column decreases with the increase of Sr, Ca and Na concentration. In the presence of 1 g of Ca and 1 g of Na, the yield of 85% was obtained for 5 mg of Sr carrier and dropped below 50% with further increase of Sr and other elements. However, the yield can be increased to 75% if Na and part of Ca are separated from Sr on the anion exchange column with alcoholic solution of nitric acid and by final separation of Ca from Sr on the Sr resin column. In the presence of large amounts of Ca, Na and other elements, isolation efficiency on the Sr resin column significantly decreases in comparison with other methods. The average yield for isolation from vegetation samples on the Sr resin column is only 21%. For the soil samples the highest average yield (78%) is obtained for the isolation in the combination of anion exchange and Sr resin columns. For the isolation from bone samples the average yields over 80% are on AnaLig®Sr01 and anion exchange resins columns, while Sr resin was not used for separation due to high content of Ca in samples. The results of the 90Sr determination in proficiency testing (PT) samples show that the accuracy of the determination does not depend on high chemical yield but depends on accuracy of yield determination. The analysis of z-values shows that 96% of obtained z-values range from 0 to ±2 while 77% of z-values range between 0 and ± 1. Ninety percent of obtained results of 90Sr determination deviate less than 20% from assigned values in PT provider reports. The results of 90Sr determination in animal bone samples using different methods are in good agreement. The results obtained by Cherenkov counting in both laboratories vary from -3.1-14.5% while results obtained by determination via 90Y and counting on i-Matic vary between -10.0 and -2.9%. These deviations are in accordance with deviations obtained with PT samples. Activity concentrations of 90Sr in wild boar bone samples range from 4 to 30 Bq kg-1 while in deer bone samples from 2 to 8 Bq kg-1.

137Cs in mushrooms from Croatia sampled 15-30 years after Chernobyl.

The aim of this study was to select species with higher potential to accumulate 137Cs among the available mushroom species, by determining the activity concentrations of 137Cs in mushrooms collected along north and north-western part of Croatia. A total of 55 samples of 14 different species were analyzed and the potential of mycorrhizal and saprotrophic species to accumulate 137Cs was compared. A wide range of the dry weight activity concentrations of 137Cs was detected, ranging from 0.95 to 1210 Bq/kg (154 Bq/kg mean value; 52.3 Bq/kg geometric mean) in mycorrhizal and 1.05-36.8 Bq/kg (8.90 Bq/kg mean value; 5.49 Bq/kg geometric mean) in saprotrophic species. Statistical analyses showed that mycorrhizal species accumulate significantly higher concentrations of 137Cs and thus could perform better as long-term bioindicators of environmental pollution by radiocaesium then saprotrophic species. The comparison of Boletus sp. and Hydnum repandum (both mycorrhizal species commonly found in Croatia) showed, in general order of magnitude, higher accumulation in Hydnum repandum. Clearly, mushrooms, especially mycorrhizal species, can be used as significant indicators even decades after the occurrence of any serious 137Cs contamination event. However, as a wide range of values indicates that various parameters may influence the total uptake of the 137Cs into the mushroom fruit bodies, it is necessary to emphasize that 137Cs activity detected in a single mushroom sample is very site-specific.