Introduction

Since the twentieth century, 90Sr has become a component of natural ecosystems presenting in natural water, soil, and biota. Strontium shows a high ability for bioaccumulation due to its affinity for bones of humans and animals resulting in elevated internal irradiation.

The presence of fission products and actinides in the environment is conditioned by the work of enterprises of nuclear fuel cycle and nuclear weapon tests. 90Sr is one of the relatively long-lived fission products with a high yield. At present, the release of anthropogenic radionuclides into the environment by the enterprises of nuclear fuel cycle is controlled strictly; however, the safety problems of radioactive waste storage facilities founded in the 1960s–1990s are still unsolved. It should be noted that these storage facilities have been under exploitation for 35–55 years, and they do not meet the modern requirements for long-term storage of radioactive waste (RW) [1]. Thus, failure of the seal and release of radionuclides into the environment is possible that may result in the appearance of an additional source of irradiation for the population and ecosystems. In such emergencies, rehabilitation measures will be required in order to provide radiation safety including the prevention of radionuclide migration in the environment. In its turn, realization of the rehabilitation measures will require regular monitoring of radionuclides activity in contaminated landscapes [1]. Regular monitoring of territories contaminated with anthropogenic radionuclides and in-time detection of radionuclides migration from RW storage facilities are necessary for the radiation safety of the population [2].

Radiation control of territories around RW storage facilities and points of radioactive waste final disposal requires very low detection limits of 90Sr in environmental samples. For example, according to the Decree of the Government of the Russian Federation No. 1847 ‘‘On approval of the list of measurements related to the scope of state regulation of ensuring the uniformity of measurements’’, the detection limit of beta emitting radionuclides (including strontium isotopes) in samples of seawater and water of surface water bodies is 0.02 Bq/L [3].

The same requirements for minimum detectable activity of 90Sr are applied to the water of control wells at points of radioactive waste final disposal. A high calcium content in groundwater and underground water makes it difficult to achieve a low minimum detectable activity (MDA) of 90Sr.

Figure 1 summarizes some methods for 90Sr determination in natural waters based on selective separation of 90Sr or its daughter 90Y. The methods include the stages of 90Sr or 90Y preconcentration from a water sample, followed by selective separation, counting source preparation, and measurement. Radionuclide preconcentration steps are based on evaporation, co-precipitation, or ion exchange chromatography; whereas, extraction chromatography is commonly used for selective separation of 90Y or 90Sr. Water samples or counting sources should be stored to achieve equilibrium between 90Sr and 90Y. The suggested methods provide minimum detectable activities within 0.001–2.4 Bq/L [4,5,6,7,8,9,10,11,12]. The methods for providing low MDA are long and labor consuming, include many operations, and require a liquid scintillation spectrometer for measurement. Preconcentration of 90Sr from seawater for further analysis is reported by Bezhin et al. [13].

Fig. 1
figure 1

The methods of 90Sr determination in natural waters

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The publications [14, 15] suggest a method for 90Sr determination in aqueous samples based on selective preconcentration of 90Sr using a carbonate-containing zirconium hydroxide (Termoxid-3 K or T-3 K sorbent produced by JSC “Inorganic Sorbents”, Zarechny city, Russia). The method provides a detection limit for 90Sr in natural waters as low as 0.02 Bq/L. The detailed characteristics of the T-3 K sorbent are described in [16, 17].

The present paper is focused on the results of testing a new method of 90Sr determination in natural waters during radioecological monitoring of natural waters in the territory of Ural Federal District, Russia. The water bodies of Sverdlovsk and Chelyabinsk regions were chosen for testing the analytical method because several enterprises of nuclear fuel cycle, RW storage facilities, and final disposal points, as well as lands contaminated as a result of nuclear weapon tests and major radiation accidents (mainly, accidents at “Mayak” PA, Chernobyl nuclear power plant (NPP) and Fukushima-1 NPP) are located in these regions.

Experimental

Characteristics of the sources of radioactive contamination and sampling points in Ural region

The East Ural Radioactive Trace (EURT) is one of the main locations of radioactive contamination in Ural region. A radiation accident at the “Mayak” PA in 1957 resulted in a release of 144Ce + 144Pr (66% of total activity), 95Zr + 95Nb (25%), 90Sr + 90Y (5.4%), 106Ru + 106Rh (3.7%) as well as 137Cs (0.35%) and plutonium isotopes (0.0043%) to the atmosphere [18] and the formation of the EURT. Today, 90Sr makes the main contribution to radioactive contamination of soils and biota due to the decay of the relatively short-lived 144Ce, 95Zr, and 106Ru. The second radiation accident at the “Mayak” PA in 1967 resulted in the formation of the “Karachay cesium radioactive trace”, which partially coincides with the territory of EURT [19]. Daily work at the “Mayak” PA resulted in intensive radioactive contamination of the Techa River since the first years of this enterprise. Low-level liquid radioactive waste from plutonium production was released to the Techa River. The period of intensive RW release to the river was in 1949–1952 [20].

The Ural region also suffered from the world’s largest radiation accident at the Chernobyl NPP. The so-called East Chernobyl radioactive trace has passed through the territory of the European part of Russia and covered some territories of Ural region. The density of surface contamination with 137Cs radionuclide in the Sverdlovsk region was 3.7–7.5 GBq/km2; however, some anomalous areas contained more than 18.5 GBq/km2 [21].

In 1988–1994, aerial gamma monitoring on a 1:10,000 scale as well as automotive and pedestrian gamma monitoring on a 1:2000 scale were performed in Yekaterinburg city (Fig. 2). Totally, 439 locations of radioactive contamination were found at the territory of Yekaterinburg city. Among them, 219 locations had dose rates above 0.6 μSv/h, 186 locations—from 1 to 10 μSv/h, 33 locations above 10 μSv/h and one point with a dose rate greater than 10,000 μSv/h was found.

Fig. 2
figure 2

The map of local areas of radioactive contamination in Yekaterinburg city, Russia [21]

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The contaminated lands remained an open source of secondary dissipation of radionuclides for a long time after the accident. Today, the release of radionuclides into river basins is conditioned by washout from radioactive drainage areas.

Radioisotopes of Кr, Xe, I, Cs, Sr, Ru, Ce etc. were released as a result of Fukushima accident [22,23,24]. According to the assessment by the Japan Atomic Energy Agency (JAEA) and the Nuclear Safety Commission of Japan, the release of 137Cs and 134Cs to the atmosphere was approximately 1.1×1016 Bq resulting in global dispersion of radiocesium, a part of which is probably deposited in Ural region.

Taking into account the radioactive contamination described above, we have chosen a number of sampling points in the territories of Sverdlovsk region and Chelyabinsk region for testing the method for 90Sr determination in natural waters. Seven samples were taken from natural water bodies in the Sverdlovsk region: Central, Nizhne-Isetsky and Verkh-Isetsky ponds (Yekaterinburg), Iset River in Kamensk-Uralsky, Beloyarsk Reservior, Volchikhin Pond and Ivdel River. Among them, Volchikhin Pond is used as the main source of tap water in Yekaterinburg city. Four natural water samples were taken in the Chelyabinsk region: Sungul Lake, Kasli Lake as well as two points in Techa River (crossing the M5 road and near Muslumovo village). Additionally, 8 water samples were collected from observing wells at a RW storage facility (Federal Ecology Operator) and 3 water samples from observing wells at a point of RW final disposal (National Ecology Operator for Radioactive Waste Treatment).

Analysis of the chemical composition of the water samples and assessment of the limitations of the method for 90 Sr analysis

The element composition of the natural water samples was determined by ICP-MS using a mass spectrometer NexION 350X (Perkin Elmer, USA) with Total Quant software.

The water samples from observing wells at a point of RW final disposal had high calcium and magnesium concentrations. Therefore, we have studied the effect of calcium concentration on Sr2+/Ca2+ separation factor and assessed the possibility of using this method for the analysis of waters with high hardness. A dependence of Sr2+/Ca2+ separation factor on calcium concentration (up to 0.6 g/L) was obtained. Certain amounts of CaCl2 were added to tap water in order to adjust the required calcium concentration. The concentration of strontium was 1 mg/L in all solutions. The time of sorption was one week. Aliquots of solutions were collected before and after sorption and analyzed by ICP-MS.

Characteristics of the method for 90 Sr determination in natural waters

Analysis of 90Sr was performed using a method developed by the Department of Radiochemistry and Applied Ecology, Ural Federal University. The method of 90Sr analysis included four main steps: sorption of 90Sr by the T-3 K sorbent, desorption of 90Sr, counting source preparation, and source measurement by beta radiometry or liquid scintillation spectrometry.

The T-3 K sorbent was a carbonate-containing zirconium hydroxide, Zr(OH)3.5(NaCO3)0.5 produced commercially by JSC Inorganic Sorbents (Zarechny town, Russia). The sorbent had a grain size of 0.4–1.0 mm, a bulk density of 1.0–1.1 kg/dm3, and a humidity of 40.0–50.0%.

The flowsheet of the method for 90Sr determination in natural waters is shown graphically at Fig. 3.

Fig. 3
figure 3

The flowsheet of the method for 90Sr determination in natural waters

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In the case of liquid scintillation spectrometry used for sample measurement, no preparation of the counting source is needed. If liquid scintillation spectrometry is unavailable, the option of eluate evaporation followed by beta radiometry of the counting source is possible for routine measurements of the samples.

In the case of beta radiometry, any beta emitting radionuclides forming sparingly soluble carbonates or any beta emitting daughter decay products of radionuclides forming sparingly soluble carbonates may interfere. However, the list of potential interferences is quite limited for the analysis of natural waters or waters from observing wells at RW storage or disposal sites.

137Cs is the main anthropogenic beta emitter. Cesium forms soluble carbonates and hydrocarbonates. It was shown experimentally that the T-3 K sorbent does not adsorb cesium.

60Co with a half-life of 5.27 years emits low energy beta particles with a maximum energy of 0.310 MeV. The counting efficiency of 60Co measurement by the UMF-2000 radiometer was 0.0457 counts per decay. A dependence of the counting efficiency of 60Co on the thickness of the counting source was obtained. Considering the counting efficiency and chemical yield of cobalt in the method, we have calculated that 60Co will contribute a significant count rate to a sample containing 0.02 Bq/L of 90Sr (MDA for 90Sr) if its activity in the water sample will be more than 1.23 Bq/L (a thin counting source) or 28.2 Bq/L (a thick counting source). Being a relatively short-lived neutron activation product 60Co, is not a common pollutant of natural water. However, in the case of the potential presence of 60Co (e.g., observing wells and waste streams at RW disposal sites), control measurement of the counting source by a gamma spectrometer is recommended.

Natural radionuclides may also interfere with the determination of 90Sr. The uranium chemical yield in the method was 7.2%. After 14 days of sample storage, the decay of 238U will result in the appearance of 33.1% of activity of the daughter 234Th. Therefore, the activity of 238U should not exceed 2 Bq/L for determination of 0.02 Bq/L of 90Sr. This is an abnormally high concentration for natural waters. Uranium presence in the counting source may be controlled via the alpha activity count rate. If the alpha count rate is significantly higher than the background count rate, gamma spectrometry measurements of the counting source will be required.

The T-3 K sorbent can uptake also 226Ra and 228Ra from natural waters if they are present there. Radium desorption from the T-3 K sorbent is rather complicated than that of strontium. This provides a lower chemical yield of radium. 226Ra is an alpha emitter, which decays to alpha emitting 222Rn and several short-lived beta emitting daughter products. Since 222Rn is an inert gas, it will emanate from the counting source during storage; thus, beta-emitting 214Pb and 214Bi should not contaminate the counting source. 228Ra is a beta emitter that has a short-lived (T½ = 6 h) beta emitting daughter 228Ac. Nevertheless, the typical activities of 226Ra and 228Ra in natural waters do not exceed several mBq/L, so low interference is expected, taking into account a lower chemical yield of radium.

Finally, a long-lived natural beta emitter 210Pb may present in natural waters and waste streams. The T-3 K sorbent adsorbs lead well with a chemical yield of 83%. However, we expect a low interference from 210Pb due to its low beta energy and low activities in natural waters.

The analysis of the natural water samples was performed according to the suggested method with measurements by a beta radiometer. The 2 L water samples were filtered through an 8–12 μm paper filter prior to analysis. Then the samples were loaded through a T-3 K sorbent column using a Masterflex L/S peristaltic pump, followed by elution of 90Sr with 1 M HCl solution. The eluate was evaporated on a 4-cm planchet. The counting source was stored for 14 days in order to achieve radioactive equilibrium between 90Sr and 90Y, followed by measurements using a low background alpha/beta radiometer UMF-2000 (Doza Company, Moscow, Russia). The volume of the eluate and measurement time were chosen, taking into account the suggested activity concentration of the sample and the relative error required.

Water samples with a natural content of stable strontium (0.03–0.66 mg/L) were analyzed. The dependence of strontium chemical yield on calcium concentration and water hardness was plotted using the results of 90Sr determination in the water samples.

Results and discussion

Characterization of sampling points and chemical composition of the natural water samples

We have collected and analyzed 16 samples of natural water from water bodies in Sverdlovsk and Chelyabinsk regions from October 2021 to May 2023. The sampling points are shown on the respective map (Fig. 4). Table 1 shows the data on pH and concentrations of alkaline earth elements in the samples of natural water collected.

Fig. 4
figure 4

Sampling points in Sverdlovsk and Chelyabinsk regions

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Table 1 Characteristics of natural water samples
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The pH values of the water samples was within 7.3–8.4 that corresponded to the maximum strontium sorption at the pH dependence curve for the T-3 K sorbent (Fig. 5). Therefore, preconcentration of strontium was conducted at the optimal pH range for the T-3 K sorbent, and the effect of pH of the samples was insignificant.

Fig. 5
figure 5

The pH dependence of the degree of strontium sorption by the T-3 K sorbent

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Table 1 shows significant variations of calcium and magnesium concentrations in natural waters—from 12.74 to 106.6 mg/L and from 3.05 to 54.5 mg/L respectively. The lowest hardness was in the water of the Ivdel’ River, whereas the Techa River and Yekaterinburg City Pond had the highest hardness. Also, the water of the Techa River contained the highest concentration of natural strontium. Concentrations of barium did not exceed 0.07 mg/L in all samples; therefore, its effect on strontium chemical yield is assumed to be insignificant.

The water samples from the observing wells at the RW disposal site contained up to 177.8 mg/L of calcium and up to 43.2 mg/L of magnesium. Such a high content of alkaline earth ions in the samples motivated us to study the effect of Ca on strontium sorption by the T-3 K sorbent and thus to assess the limitations of the suggested method.

The study of the sorption properties of the T-3 K sorbent for strontium in the presence of calcium up to 600 mg/L

Alkaline earth ions may show a competitive effect on strontium sorption by the T-3 K sorbent. The Eqs. 1 and 2 describe the mechanism of strontium sorption by the T-3 K sorbent:

$$ 2 \equiv {\text{Zr - CO}}_{{3}} {\text{H + Sr}}^{{2 + }} {\text{ + 2H}}_{{2}} {\text{O}} \to \begin{array}{*{20}l} { \equiv {\text{Zr - CO}}_{{3}} \backslash } \hfill & {} \hfill \\ {} \hfill & {{\text{Sr + 2H}}_{{3}} {\text{O}}^{ + } } \hfill \\ { \equiv {\text{Zr - CO}}_{{3}} {/}} \hfill & {} \hfill \\ \end{array} $$
(1)
$$ {2} \equiv {\text{Zr - CO}}_{{3}} {\text{Na}} + {\text{Sr}}^{{{2} + }} \to \begin{array}{*{20}l} { \equiv {\text{ Zr}} - {\text{CO}}_{{3}} \backslash } \hfill & {} \hfill \\ {} \hfill & {{\text{Sr}} + {\text{ 2Na}}^{ + } } \hfill \\ { \equiv {\text{ Zr}} - {\text{CO}}_{{3}} /} \hfill & {} \hfill \\ \end{array} $$
(2)

Distribution coefficient of strontium sorption by the T-3 K sorbent is (1.3 ± 0.6) 104 mL/g [17]. Sorption occurs due to the formation of a sparingly soluble strontium carbonate, which is characterized by a low solubility product Ksp (SrCO3) = 5.3×10–10. The affinity of the sorbent for the alkaline earths follows in the series Sr > Ba > Ca > Mg, which is determined by a decrease of solubility of their carbonates. The solubility products of alkaline earth carbonates are MgCO3 = 7.9 × 10–6, CaCO3 = 4.4 ×10–9, SrCO3 = 5.3 × 10–10, BaCO3 = 4.9 × 10–9 [25].

Figure 6 demonstrates a dependence of Sr2+/Ca2+ separation factor on calcium concentration (up to 600 mg/L).

Fig. 6
figure 6

The dependence of Sr2+/Ca2+ separation factor on calcium concentration

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Separation factor R (Sr2+/Ca2+) decreased with the increase in calcium concentration but remained almost constant (2–2.2) within the calcium concentration range of 50–600 mg/L.

The maximum separation factors for Sr/Ca and Sr/Mg on the T-3 K sorbent were achieved in case of strontium preconcentration from a spring water containing 13.96 mg/L of Ca and 16.37 mg/L of Mg; the respective values were R (Sr2+/Mg2+) = 74.0 and R (Sr2+/Ca2+) = 51.2 [26]. High separation factors were also obtained for low mineralized water containing 14.3 mg/L of calcium: R (Sr2+/Mg2+) = 12.8 and R (Sr2+/Ca2+) = 8.9 [14].

Thus, the suggested method can be applied for the analysis of water samples with high hardness due to good Sr/Ca separation factors even at high calcium concentrations and the high static exchange capacity of the T-3 K sorbent (44 ± 6 mg/g [17]). This was approved by a series of experiments on strontium preconcentration from waters with a wide hardness range.

Assessment of the effect of calcium concentration and water hardness on strontium chemical yield in the method

Figure 7 demonstrates the dependence of strontium chemical yield on calcium concentration in the sample.

Fig. 7
figure 7

The dependence of strontium chemical yield on calcium concentration in the sample

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In the case of 16 water samples with a volume of 2 L, the average strontium chemical yield was 81 ± 2% decreasing only at the calcium concentration of more than 76 mg/L or total water hardness of more than 5.2 mmol/L. Only two of the 16 tested natural water samples had higher concentrations of alkaline earth elements–the water in the Techa River near Muslumovo village and the spring in Deevo village. An increased salt content in the Techa River was associated with the shallowing of the river due to drought and evaporation of water. In the case of water from the Techa River, the strontium chemical yield was 54.6%. The samples from the RW disposal site demonstrated a much higher hardness. Nevertheless, strontium yield remained as high as 66.5 ± 1.5% even at calcium concentrations up to 177.8 mg/L.

The minimum detectable activity (MDA) was calculated by two methods, taking into account the worst conditions: the strontium yield = 54.6% and the counting efficiency = 0.143 counts per decay. According to an approach described in [14], we have calculated the MDA value taking into account the strontium yield, counting time, counting efficiency, and sample volume; the MDA value was 0.02 Bq/L. Alternatively, we have calculated the MDA value in accordance with ASTM Standard [27] by Eq. 3:

$$ {\text{MDA}} = \frac{{2.71 + 4.66\sqrt {I_{{\text{b}}} } }}{t \times Y \times \varepsilon } $$
(3)

where Ib is the blank count rate, ε is the counting efficiency, t is the counting time, and Y is the chemical yield. The respective MDA value was 0.003 Bq/L.

The results of determination of 90 Sr activity concentrations in natural waters from Sverdlovsk and Chelyabinsk regions

Activity of the samples were calculated according to the Eq. 4 taking into account the counting efficiency for equilibrium 90Sr–90Y by the UMF-2000 beta radiometer:

$$ {\rm A} = I/\varepsilon $$
(4)

where A is activity of the counting source, Bq; I is the count rate, cps; ε is the counting efficiency, counts per decay. Figure 8 shows the dependence of the counting efficiency on the thickness of the counting source.

Fig. 8
figure 8

The dependence of the counting efficiency on the thickness of the counting source

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Table 2 shows the results of the determination of 90Sr activity concentrations in the water samples as well as 90Sr/137Cs ratios in them.

Table 2 Activity concentrations of 90Sr in natural waters collected at Sverdlovsk and Chelyabinsk regions
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The water samples collected from Techa River contained the highest activities of 90Sr (~ 50 Bq/L) that is conditioned by the release of low-level liquid radioactive wastes into the river from Mayak PA in 1950s. All other water samples have shown activities of 90Sr ranging from 0.02 to 0.16 Bq/L, which is much less than the allowed limit of 90Sr in drinking water in Russia (4.9 Bq/L according to the Russian National Norms of Radiation Safety-99/2009 [28]).

An elevated content of 90Sr (excluding water from the Techa River) was found in the water from Nizhne-Isetsky Pond (Yekaterinburg). Monitoring of seasonal variations of 90Sr in this pond has shown a 90Sr activity concentration (in equilibrium with 90Y) of 0.16 ± 0.02 Bq/L in November 2021. Then activity decreased to 0.02–0.03 Bq/L in spring, summer, and autumn. Probably, contamination of Nizhne-Isetsky Pond with 90Sr was conditioned by the transfer of this radionuclide from the bottom sediments of this pond as well as runoff from contaminated soils. In winter, the pond freezes, and the flow rate decreases, resulting in an increase of the radionuclide concentration in the water.

90Sr/137Cs activity ratios were determined in the water samples in order to determine the potential source contamination. Analysis of 137Cs activity concentration was performed in the same water samples; the results were reported in [29]. It can be supposed that atmospheric fallouts after the Chernobyl disaster in 1986 were the most probable source of contamination of the soils and bottom sediments affecting the radioactivity of Nizhne-Isetsky Pond since the typical 90Sr/137Cs ratio in the Chernobyl radioactive trace is 0.1–0.2 [21]. The 90Sr/137Cs ratio in the Ivdel River was found to be 0.21, indicating Chernobyl fallouts as the source of radioactive contamination too. The Ivdel River also flows through the northern zone of the Chernobyl radioactive trace.

Contamination of water in Verkh-Isetsky Pond and Central City Pond (Yekaterinburg) showed the values of 90Sr/137Cs activity ratios within 0.4–0.6 that is typical for global fallouts after nuclear weapon tests. The values of the 90Sr/137Cs activity ratio in the water from the Techa River, the Iset River near Kamensk-Uralsky city, and Beloyarsk Reservior significantly differed from those values typical for Chernobyl fallouts and global fallouts. This can be explained by the fact that these water bodies are located in the influence zones of nuclear fuel cycle enterprises, or EURT.

The results of monitoring were compared with the literature data (see Table 3). There is no open data on the systematic monitoring of 90Sr in the natural waters of Ural region; the available data are fragmentary and refer to different years. Also, there is no literature data on monitoring of 90Sr in the water of the Iset River in Yekaterinburg, the Ivdel River and the Volchikhin Pond.

Table 3 Activity concentrations of 90Sr in some natural surface waters of Ural region
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In case of large water bodies such as the Sungul Lake, the Kasli Lake, and the Beloyarsk Reservoir, our determined activities of 90Sr were quite similar to the literature data. However, the experimental data may differ significantly from the literature data in the case of small water bodies, where water levels may vary depending on precipitation. So, our data for the Techa River near Muslumovo village exceeds the reported data in 2010 by 35%. This difference may be due to the dry summer of 2021 resulting in the evaporation of water in the river and concentration of radionuclides.

The results of the study have shown also that the activities of 90Sr in water samples from observing wells did not exceed the control levels.

Conclusions

Testing a new method for determination of 90Sr in natural waters based on selective preconcentration of strontium by a T-3 K carbonate-containing zirconium was performed during the radioecological monitoring of natural waters in the territories of Sverdlovsk region and Chelyabinsk region (Middle Urals, Russia).

The dependence of strontium chemical yield on calcium concentration in the sample was obtained. It was shown that strontium chemical yield of 81 ± 2% was constant for the samples containing up to 76 mg/L of calcium or ≤ 5.2 mmol/L of total hardness salts. The strontium yield decreased to 66.5 ± 1.5% at higher calcium concentrations up to 177.8 mg/L. The minimum detectable activity of 90Sr in 2 L water samples was calculated to be 0.02 Bq/L.

Activity concentrations of 90Sr were determined in 16 samples of natural waters from water bodies in the influence zones of nuclear weapon tests at the Novaya Zemlya testing venue, Chernobyl radioactive trace, East Ural radioactive trace, as well as the daily activity of nuclear fuel cycle enterprises. The monitoring of 90Sr activity was performed for the first time for some of the natural water bodies. In addition, the method was tested using 8 samples from observing wells at a radioactive waste storage facility and 3 samples from observing wells at a point of radioactive waste final disposal.

It was shown that the water samples collected from the Techa River near Muslumovo village contained the highest activity of 90Sr (56 ± 3 Bq/L in equilibrium with 90Y). The activities of 90Sr in all other water samples were much less than the allowed limit of 90Sr in drinking water in Russia (4.9 Bq/L). The activities of 90Sr in water samples from observing wells did not exceed the control levels.

It was established that contamination of the water of Nizhne-Isetsky Pond (Yekaterinburg) by 90Sr occurred because of runoff from contaminated coastal soils. Seasonal variations of 90Sr activity concentration in this pond were studied. The maximal 90Sr activity in the pond (0.16 Bq/L) was found in winter. Chernobyl fallouts were suggested as the most probable source of contamination in the pond.