Elsevier

Journal of Sea Research

Volume 176, October 2021, 102112
Journal of Sea Research

Bio-kinetics of cesium-137 in Mediterranean mussel (Mytilus galloprovincialis) and sea snail (Rapana venosa) via seawater exposure

https://doi.org/10.1016/j.seares.2021.102112Get rights and content

Highlights

  • The accumulation and depuration process was slower in large-sized organisms.

  • The highest concentration factor was calculated for small sized mussels.

  • Body size of organisms in the accumulation experiments was statistically significant.

  • The biological half-lives were calculated high for small sizes in both organisms.

Abstract

Accumulation and depuration kinetics in the samples of mussel (Mytilus galloprovincialis L. 1758) and sea snail (Rapana venosa (Valenciennes, 1846)) exposed to 137Cs radioisotope via seawater exposure were investigated under laboratory conditions. Accumulation and depuration kinetics were monitored for 49 and 59 days, respectively. Concentration factor and biological half-life values were calculated from the accumulation and depuration kinetics of mussel and sea snail samples. Concentration factors at equilibrium were 16.25 ± 4.41 and 19.50 ± 1.17 for large and small mussels, respectively, while 16.34 ± 0.70 and 14.31 ± 0.63 for large and small snails, respectively. The biological half-lives at slow components were 38.50 and 77.00 days for large and small mussels, respectively, while 49.50 and 57.75 days for large and small snails, respectively. Compared to the literature, the slightly higher concentration factor and biological half-life values obtained in this study for both mussel and snail samples may help to identify these species as bio-indicators of the 137Cs radioisotope in the marine environment. In addition, it was statistically determined that body size is an important parameter for both living organisms in bioaccumulation experiments unlike the depuration experiments. In the light of all these results, it has been determined that mussel and sea snail organisms are extremely valuable indicators in terms of reflecting radioactive pollution in the sea in monitoring the 137Cs radioisotope for possible inputs of any radioactive pollution in the marine environment.

Introduction

Since the 1950s, marine biological ecosystems have occasionally been exposed to radionuclide pollution from industries, nuclear accidents, and nuclear weapons testing and their use. Artificial radionuclides such as 137Cs, 90Sr, 239Pu and 240Pu have been released to the environment at certain rates due to nuclear weapon tests and nuclear power plant (NPP) accidents, such as Chernobyl in Kiev, Ukraine and the Daiichi Nuclear Power Plant accident in Fukushima, Japan (Geras'Kin et al., 2008; Ikäheimonen et al., 2009; Sawidis et al., 2010; Sezer et al., 2014). Radionuclides reach the marine environment as a result of direct transport from the atmosphere and indirectly through rivers due to meteorological events. Radionuclides that reach the marine environment become an integral part of the marine ecosystem (water, sediment, biota) and can be transported to humans through the food chain (Akram et al., 2006; Kalaycı et al., 2013). Therefore, it is very important to know the sources and routes of natural and anthropogenic radionuclides to the marine environment in order to ensure protection of human health and the environment. The concentration levels of radionuclides in the marine environment of the Black Sea have increased due to the progressive development of the nuclear industry of countries linked to the Black Sea via rivers. In addition, radionuclide concentrations increased markedly in the Black Sea after the Chernobyl Accident (Güngör et al., 2001; Kalaycı et al., 2013). Being also a closest marine basin to the Chernobyl site, the Black Sea and its broad drainage areas have received in 1986 substantial amount of the long-lived artificial radionuclides, particularly 90Sr, 137Cs, and plutonium isotopes, released into the atmosphere from the damaged nuclear reactor and delivered with the air masses moving south- and westward from the accident area 137Cs, a fission product radioisotope, is one of the major radionuclides released after the Chernobyl reactor accident. As a result, concentration of man-made radionuclides in the Black Sea surface water increased sharply, exceeding the pre-Chernobyl levels by several times. In 1987, the total radionuclide inventory in the Black Sea water was of 2120 ± 420 TBq 137Cs and 850 ± 190 TBq 90Sr (Gulin et al., 2013). Therefore, 137Cs activity concentrations are the key factors in an assessment of the radiological hazard to marine organisms and humans. It is the main long-lasting component of radioactive fallout from nuclear weapon testing (Isaksson and Erlandsson, 1998; Kalaycı et al., 2013). Cesium radioisotopes cause both internal and external irradiation due to their chemical resemblance to potassium as well as emitting beta particles and gamma rays. For this reason, the cesium radioisotope accumulating in the soft tissue of marine organisms is very important for humanity in terms of entering the food chain (Kalaycı et al., 2013; Sangvanich et al., 2010).

Mollusks are one example of aquatic organisms that have demonstrated the ability to be a potential bio-indicator and accumulate metals and radionuclides to high concentrations (Kanakaraju and Anuar, 2009). They are very useful bio-indicator organisms used in the monitoring of metal/radioactive pollution in the aquatic environment (Bat et al., 2000). Filter-feeding organisms, bivalves have a sedentary life, so they are directly influenced by environmental conditions. Mediterranean mussels (Mytilus galloprovincialis L. 1758) are invasive warm-water species that have spread throughout the world's aquatic environments (Assunta Meli et al., 2008). Mediterranean mussel M. galloprovincialis is a bivalve species with a wide geographical distribution. It is well known that soft tissues of mussels provide a reflection of the quantities of radioactive contaminants introduced to the global ecosystem (Florou et al., 2004). M. galloprovincialis is widely used to monitor metal/radioactive pollution because it is consumed by humans (Bat et al., 1999; Özden et al., 2010). Rapana venosa (Valenciennes, 1846) is a species of biomonitoring sea snail of Asian origin known as an aggressive predatory species. These species, which transported the Black Sea in larval form from the ballast waters of the ships and spread rapidly throughout the Black Sea, damaging the mussel stocks were first reported in the Black Sea in 1947 (Moncheva et al., 2011; Mülayim and Balkıs, 2015). The main diet of snail R. venosa, defined as a hunter and predator, consists of mollusk species and mussels. These demersal species are extremely important for energy transfer between trophic levels and to reveal environmental conditions of coastal regions (Bat et al., 2016). Moreover, mollusks, which have very important nutritional value such as high protein, vitamin and mineral content, are also rich in unsaturated fatty acids. They contain all the amino acids that exist in nature. In addition to being such a valuable and important food source, mollusks can pose significant risks to human health as they accumulate various pollutants, including toxic substances, in their soft tissues (Benali et al., 2017; Bilandžić et al., 2016; Gedik, 2018; Tacon and Metian, 2013; Thilsted et al., 2014).

Bio-indicator is a term used to describe living organisms that well describe the ecological state of the habitat in which they live. In the case of metal/radioactive contamination, bio-indicator types must accumulate high levels of pollutants to better evaluate the pollution level. Therefore, controlled bio-kinetic experiments conducted under laboratory conditions are needed to determine the rate of accumulation and depuration of pollutants in marine organisms. The bio-kinetic behavior of cesium radionuclides in different mussel species has also been studied both in the laboratory and in situ under the marine environmental conditions of the Turkish sea and other countries (Güngör et al., 2001; Kalaycı et al., 2013; Metian et al., 2011; Pouil et al., 2015; Topcuoglu and Van Dowen, 1997). In addition, considering the literature, a study was conducted by Onat and Topcuoǧlu (1999) on the depuration kinetics of Zn and 134Cs in marine snails. No attempt has been made so far to determine the accumulation and depuration kinetics of 137Cs of the marine snail (R. venosa). Moreover, in previous studies, the accumulation and depuration of Chernobyl radionuclides in different marine organisms have been studied in different aquatic environments (Metian et al., 2016; Onat and Topcuoǧlu, 1999; Prihatiningsih et al., 2016; Sezer et al., 2014; Topcuoglu et al., 2001; Topcuoĝlu et al., 1996). Bio-kinetic changes of 134Cs were generally investigated in studies. 137Cs, a fission product, is one of the major radionuclides released into the Black sea environment after the Chernobyl accident. It is the main long-lived component of radioactive fallout arising from nuclear weapon tests. 134Cs is also a fission product which is emitted to environment from nuclear weapon tests and nuclear power plant accidents. However it is not available in the environment because of its short physical half-life (2.06 years) compared to 137Cs (Kalaycı et al., 2013). For this reason, the three main goals of this study were: (1) to determine the concentration factors (CFss) from the accumulation kinetics of 137Cs via seawater exposure in Mediterranean mussels and sea snails (2) to obtain the biological half-lives (Tb1/2) from the depuration kinetics of 137Cs (3) to statistically assess the effect of different sizes in accumulation and depuration experiments. Thus, the bio-kinetic data obtained for the bio-indicator organisms of interest as a result of this research will be very useful in revealing the extent of the pollution created by the radionuclides released into the aquatic environment as a result of the developing nuclear breakthroughs all over the world.

Section snippets

Sampling and acclimation

Mussel (M. galloprovincialis) and snail (R. venosa) organisms were collected by scuba or free diving (2–40 m depth) in July 2015 from the position inside Rize port in the Rize province in Turkey (41°02′11′′ N–40°30′57′′ E). The sampled organisms were then placed in ice boxes and immediately transported to the laboratory. The epifauna and sediment residues adhering to the shell parts of the mussel and snail samples were removed with a brush and scalpel, and the samples were then washed with

Results and discussion

No mortality of mussels and snails was recorded during the acclimation period and during the different experiments. Exposure via seawater was carried out for a period of 49 days, during which time the accumulation kinetics of 137Cs accumulation in mussels and snails were studied. The accumulation kinetics of 137Cs was best described by a first-order exponential model for the whole soft tissue of the mussels and snails.

The fit curves obtained for both sizes of mussel samples are given in Fig. 1.

Conclusion

The present study provides current information about accumulation and depuration bio-kinetics of 137Cs radioisotope in different marine bio-indicators such as mussel and sea snail. The slightly high concentration factors (CFss) and high biological half-lives obtained for both snail and mussel samples in the current study may contribute to the identification of these species as bio-indicators of 137Cs in the marine environment. In addition, it was concluded that size is an important parameter

Declaration of Competing Interest

None.

Acknowledgments

This work was supported by the Scientific and Technical Research Council of Turkey (TUBITAK) (ÇAYDAG, Project No: 114Y652) in 2014.

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