A team of FLNP JINR scientists and their colleagues from the Stellenbosch University (South Africa) utilised neutron activation analysis for complex marine biomonitoring studies. In 2022, the researchers received the JINR Encouraging Prize for a series of papers devoted to determining the concentrations and origin of micro- and macroelements in mussel samples from coastal areas of South Africa.

Mussels are one of the best-known groups of bivalve mollusks that are an important component of marine and ocean ecosystems. Mussels play the role of filtering organisms by feeding on plankton, and make a significant contribution to the purification of water resources from various pollutants. They are also a source of food for many animals and people.

Bivalve mollusks can accumulate high concentrations of micro- and macroelements, including heavy metals, due to specific absorption mechanisms. Owing to this, mussels are widely used as biomonitors of pollution of coastal areas with heavy metals, microplastics and various organic compounds and often become objects of scientific research.

A group of scientists from FLNP JINR has been studying marine bivalves collected in various parts of the world ocean for more than 10 years. Marina Frontasyeva, Advisor to the FLNP Directorate, and Inga Zinicovscaia, Head of the FLNP Sector of Neutron Activation Analysis and Applied Research, told about how these studies began and how they were conducted.

First sampling sites (yellow) in South African waters

“As always, chance helped. In 2012, during my business trip to South Africa to the Faculty of Science at Stellenbosch University, I met Jacques Bezuidenhout, a professor at the Faculty of Military Science, who was invited to lunch by colleagues from the Faculty of Science,” says Marina Frontasieva.– During our conversation over lunch, Jacques mentioned that he also owns a mussel farm that supplies local restaurants. To gain access to such experimental material as a continuation of our research with freshwater mollusks from the Rybinsk Reservoir in Russia – isn’t this a stroke of luck?! So, returning to Russia, I was already carrying with me frozen mussels collected from two contrasting sites on the Atlantic coast of South Africa – from the enclosed Saldanha Bay and the open Danger Bay. This is how the JINR-South Africa joint environmental project “Mussel Watch Program” began.”

Jacques Bezuidenhout, Zoya Goryaynova, Dmitry Pavlov (I.D. Papanin Institute for Biology of Inland Waters, RAS), Marina Frontasyeva, Inga Zinicovscaia

“Our aim was to assess the ecological condition of the coastal areas. The main task was to determine which elements are accumulated in mussels collected from different sites, and whether these elements are of natural or anthropogenic origin. And we succeeded,” says Inga Zinicovscaia. “In addition to the environmental assessment, our goal was to assess food safety, since mussels are the most affordable source of natural food besides fish for the local population.”

Marina Frontasieva and Pavel Nekhoroshkov

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Over time, the researchers deepened these studies and expanded the geography of sampling locations, covering countries neighboring South Africa: mussels for the study were collected from the coastal areas of South Africa, Namibia and Mozambique. All sampling sites were chosen as the most representative in terms of the availability of mussels, stability of environmental parameters and differences in the degree of contamination in accordance with the results already published in the literature.

Map of mussel sampling sites in Mozambique, South Africa and Namibia. The big star is Cape Town, a transit point from the Atlantic Ocean to the Indian Ocean

To determine the elemental composition of the samples, neutron activation analysis was used as the main analytical method at the REGATA facility of the IBR-2 reactor at FLNP JINR.

The essence of the method is that samples of mussels (soft tissues and shells) were bombarded with neutrons, resulting in the formation of radioactive isotopes with short and long half-lives. By processing the induced activity spectra and using auxiliary software, the scientists determined the concentrations of elements in the samples. The main advantage of the method is its high sensitivity: unlike other methods, neutron activation analysis makes it possible to determine a large number of elements (up to 50 at the IBR-2 reactor), including those contained in samples in very low concentrations, which is typical, for example, for heavy metals, as well as halogens.

Thus, during the study of shells and soft tissues of mussels, the researchers identified about 25 macro- and microelements in their composition. Some of them, such as Al, Cr, Co, Fe, Ni, Zn, As, Se, I, are considered potentially dangerous to living beings, including humans. For these elements, the researchers calculated the risks associated with consumption of mussels by the local population, and in many samples, the concentrations of toxic elements exceeded the maximum permissible levels for fish products established by the World Health Organization (WHO). Weekly consumption of more than 250 g of fresh mussels per person can significantly increase the risk to human health because of the potential intake of hazardous substances.

Sample preparation in the chemical laboratory of the FLNP Sector of NAA and Applied Research. Inga Zinicovscaia and students of Stellenbosch University

A concomitant result of the research was the identification of the supposed sources of entry of elements into the organisms of mussels and, as a consequence, humans, according to the main groups: terrigenous, that is, during the formation of elements from the products of weathering of rocks (Al, Sc, V, Cr, Mn, Fe, Rb, Cs, Th), anthropogenic (Co, Ni, Sb), hydrogenous (Na, Mg, Cl) and mixed (As, Br, I, Zn, Se).

At the same time, despite the fact that maritime transport and various kinds of pollution (wastewater; agricultural, commercial and urban development; power plants; accidental emissions) in coastal areas significantly burden the ecosystem, mussels farmed in closed water areas contain lower concentrations of detected elements compared to mussels living in stressful natural conditions.

“Wild mussels live in the open ocean, so rapid and constant changes in wave activity can cause stress to these organisms. According to our data, this process is reflected in high concentrations of such elements as Na, Mg, Cl, V, Cr, Fe, Zn, As, Br, Sr, I and U in soft tissues and Al, Cl, Cr, Fe, Zn, Sr and I in shells,” emphasized Inga Zinicovscaia.

The obtained data, the researchers note, can be used for future biomonitoring studies, for recreational purposes, food production, the development of mariculture, as well as for assessing the safety of the environment for the local population.

Studies nominated for the JINR Prize:

1. Nekhoroshkov, P.S., Bezuidenhout, J., Frontasyeva, M.V., Zinicovscaia, I.I., Yushin, N.S., Vergel, K.N. and Petrik, L., 2021. Trace elements risk assessment for consumption of wild mussels along South Africa coastline. Journal of Food Composition and Analysis, 98, p.103825. https://doi.org/10.1016/j.jfca.2021.103825
2. Nekhoroshkov, P., Zinicovscaia, I., Nikolayev, D., Lychagina, T., Pakhnevich, A., Yushin, N. and Bezuidenhout, J., 2021. Effect of the Elemental Content of Shells of the Bivalve Mollusks (Mytilus galloprovincialis) from Saldanha Bay (South Africa) on Their Crystallographic Texture. Biology, 10(11), p.1093. https://doi.org/10.3390/biology10111093
3. Nekhoroshkov P, Bezuidenhout J, Zinicovscaia I, Yushin N, Vergel K, Frontasyeva M. Levels of Elements in Typical Mussels from the Southern Coast of Africa (Namibia, South Africa, Mozambique): Safety Aspect. Water. 2021; 13(22):3238. https://doi.org/10.3390/w13223238