238U, 232Th, 40K and 137Cs activity concentrations along the southern coast of the Caspian Sea, Iran
Introduction
There are many naturally occurring radionuclides in the environment, including isotopes of cesium, uranium and thorium. The average natural uranium abundance in the earth’s crust is 2.7 μg g−1, and 3 × 10−6 g L−1 in typical sea water (Mora et al., 2004). Interest in determining levels of these radionuclides mainly stems from their usefulness as environmental tracers. If environmental samples have a high concentration of uranium and thorium, determining the levels of radionuclides in sea water, soil and sediment is important for protection from radiation.
In addition to naturally occurring radionuclides, a large number of radionuclides have been produced and released into the environment by human nuclear activity, including nuclear weapons testing, the operation of nuclear power plants, research reactors, and nuclear fuel reprocessing. Nuclear accidents, such as the Chernobyl accident, have also released large amounts of radionuclides into the environment. Therefore, isotopic determinations of natural and anthropogenic radionuclides are required for environmental monitoring, nuclear safeguards, and nuclear forensic studies (Eisenbud and Gesell, 1997).
The Caspian Sea is surrounded by Azerbaijan, Russia, the Islamic Republic of Iran, Kazakhstan and Turkmenistan. With a surface area of 390,000 km2, the Caspian Sea is the world’s largest inland water body (Froehlich et al., 1999). The sea is 1200 km long and varies between 204 and 566 km in width, with an average width of 330 km. About 130 rivers of varying size drain into the Caspian Sea, providing an annual input on the order of 300 km3 (Froehlich et al., 1999). Major river inputs include the Volga, Ural and Terek, with a combined annual flow account for 88% of the total flow (approximately 370 km3 per year). The Sulak, Samur, Kora and a number of smaller rivers contribute approximately 7% of the flow, and the remainder comes from the rivers of the Iranian shore (Boulyga and Heumann, 2006). The dynamics of water circulation within the Caspian Sea were not previously known, but combined oceanographic and isotopic investigations carried out within the framework of the IAEA supported projects have brought new insights into these processes (Boulyga and Heumann, 2006). The nature and circulation of water masses in the Caspian Sea is shown in Fig. 1, with two types of cyclonic eddy currents present in the central and southeastern regions. In the southern coastal region of the Caspian Sea, currents are directed towards the northwest, north, southeast and south, with average speeds of 20–40 cm s−1 and a maximum speed of 50–80 cm s−1. Therefore, this water flow drives pollutants from the central and northern coasts towards the south coast. Calculations by Vakulovsky and Chumichev (1998) show that from 1962 to 1976, the transfer of 90Sr from the Volga and Kora rivers to the Caspian Sea amounted to 70 TBq (Vakulovsky and Chumichev, 1998).
Coastal sedimentary deposits are important indicators of climate change and sea-level fluctuations in the Caspian Sea area. Sedimentation is also one of the factors known to cause variation in the volume of the Caspian Sea basin over long periods of time (Federov, 1995, Klige and Selivanov, 1995). Geological processes have influenced the water balance of the Caspian catchments basin by altering the watershed and thus diverting river courses to other basins (Varushchenko et al., 1987).
Research was conducted by the IAEA in August–September 1995 and in 1996 to measure anthropogenic radionuclides, oceanographic and isotopic investigations of 3H and 3H–3He in order to study water balance and dynamics. Together with studies by the Iran Nuclear Regulatory Authority conducted to measure natural uranium concentrations in the Caspian Sea, results show that the measurement of radionuclides in sediments is necessary for the southern part of the Caspian Sea (Froehlich et al., 1999, Garshasbi et al., 2005, Oregioni et al., 2003).
Section snippets
Sampling
The regional sampling was conducted using the systematic random sampling method according to the international standard (Mamoney and Khater, 2004, ASTM, 1995). Samples were taken from 40 polluted marine sites in the southern Caspian Sea, ranging from 53° 05′ 84″ N, 36° 48′ 52″ E to 48° 53′ 60″ N, 38° 14′ 05″ E, in March 2007. Ten samples with a depth of 5 and 10 cm subsurface were taken, each sample being about 20 m apart. Samples with particle size greater than 2 cm were discarded. Sediment
Results and discussion
The mean activity concentration of 238U and 232Th series, 40K and 137Cs (Bq kg−1 dry weight) in the soil and sediment samples are shown in Table 1. Table 2, Table 3 give the values of mixed gamma reference material activity and international recommended limits, respectively (UNSCEAR, 1998).
A comparison of Table 1, Table 3 reveals that the average concentration of 238U is higher than the International Limits: this was true for a large majority of samples (about 80%). Measured activities of the
Conclusions
The data obtained in this work cover a wide area in the north of Iran along the Caspian Sea coast, and can be considered as a base-line for the region. The lowest concentration of uranium (22 ± 1.3 Bq kg−1) was observed in Rudsar sediment and the highest concentration (177 ± 12.4 Bq kg−1) was seen in Kenar-Darya soil. Similarly, the lowest (16 ± 1.5 Bq kg−1) and highest (117 ± 11.5 Bq kg−1) levels of 232Th were found in Sisangan sediment and Anzali soil. This indicates that these radioactive minerals are
Acknowledgements
The authors wish to thank the Office of Graduate Studies of the University of Isfahan for their support. They would also like to thank Mr. Afshar, director of the Mazandaran Meteorology Office, Iran, and central laboratory, University of Isfahan, for their assistance.
References (16)
- et al.
Determination of extremely low 236U/238U isotope ratios in environmental samples by sector-field inductively coupled plasma mass spectrometry using high-efficiency sample introduction
Journal of Environmental Radioactivity
(2006) - et al.
Isotope studies in the Caspian Sea
Science of the Total Environment
(1999) - et al.
Environmental pollutant isotope measurements and natural radioactivity assessment for North Tushki area, south Western desert, Egypt
Applied Radiation and Isotopes
(2002) - et al.
Distribution of natural radionuclides and hot points in the coasts of Hormozgan, Persian Golf, Iran
Journal of Radioanalytical and Nuclear Chemistry
(2006) - et al.
Distribution of radioactive pollution of 238U, 232Th, 40K and 137Cs in northwestern coasts of Persian Gulf, Iran
Marine Pollution Bulletin
(2008) - ASTM, 1995. American Society for Testing and Materials. Standard Practice for Sampling Surface Soil for Radionuclides,...
- et al.
Environmental Radioactivity
(1997) Modern geology of the Caspian Sea
Russian Academy of Science Bulletin
(1995)
Cited by (65)
Radioactive risk assessment of beach sand along the coastline of Mediterranean Sea at El-Arish area, North Sinai, Egypt
2022, Marine Pollution BulletinNatural radioactivity in the prospecting tunnel in Egypt: Dose rate and risk assessment
2021, Radiation Physics and ChemistrySpatial distribution, radiological risk assessment and positive matrix factorization of gamma-emitting radionuclides in the sediment of the Boka Kotorska Bay
2021, Marine Pollution BulletinCitation Excerpt :Research conducted in North Cyprus (Abbasi and Mirekhtiary, 2020) revealed the average activity concentration of 40K in the sediments higher than the worldwide values. Reza Abdi et al. (2009) reported significant radioactive contamination of the marine sediment in the southern coast of the Caspian Sea. A frequently used approach in the radionuclides data evaluation is to apply correlation analysis and some multivariate analysis, such as hierarchical cluster analysis (HCA) (Dragović and Onjia, 2007; Ravisankar et al., 2015; Devanesan et al., 2020; Qureshi et al., 2014; Yakovlev and Puchkov, 2020; Ghias et al., 2021).