Mercury (Hg) bioaccumulates and magnifies through the trophic chain, leading to significant social, environmental, and human health impacts. Selenium (Se) has been proposed as a counteracting agent to Hg toxicity, yet its behavior and mechanisms of interaction within organisms are still poorly understood. The Amazon region is one of the areas most heavily impacted by Hg worldwide. Hg significantly bioaccumulates in local fish species, and riverside communities rely heavily on these fish as a primary part of their diet [1].

Despite the growing interest in the characterization of tiemanite (HgSe) nanoparticles, considered key in Hg detoxification processes in vivo in a variety of marine fish species, there is no report to date of their presence in tropical and continental regions, particularly in freshwater fish. This study aims to explore and characterize Hg and Se nanoparticles in Amazonian fish species. Enzymatic extraction was performed to isolate Hg and Se nanoparticles from the liver and muscle tissues of animals with different dietary habits (carnivorous and non-carnivorous). A total of 50 selected samples were analyzed by Inductively Coupled Plasma Mass Spectrometry in single particle mode (spICP-MS) in which 202Hg, 78Se and 111Cd were monitored. Through these analyses, Hg and Se nanoparticles were identified in the liver and muscle tissues of all carnivorous species investigated (Cichla temensis – Tucunaré, Pseudoplatystoma fasciatum – Caparari, Arapaima sp. – Pirarucu).

Regarding non-carnivorous species, Hg and Se nanoparticles were detected only in the muscle tissue of Pterygoplichthys pardalis – Acarí, with mean size of 58 ± 17 and 81 ± 25, respectively. However, for Leporinus sp. (Aracu) Se nanoparticles but not Hg nanoparticles were detected in muscle and liver. For the first time, the presence of Hg and Se particulate is reported in Amazonian fish and the obtained values are comparable with those reported in marine species [3]. Interestingly, Cd nanoparticles were also found, although not in all fish species. They were present in the muscle and liver of Cichla ocellaris (Tucunaré). In non-carnivorous species, Cd nanoparticles were identified in the muscle of Acarí and liver of Aracu. This finding aligns with observations in marine animals, suggesting that the process leading to Hg and Se biomineralization may also sequester other toxic elements, such as Cd [4, 5]. In summary, this study presents the first evidence of Hg and Se nanoparticles in Amazonian fish and, more broadly, in freshwater species, providing crucial insights into Hg detoxification processes in freshwater ecosystems.

References

[1] M.E. Crespo- Lopez, M. Augusto-Oliveira, A. Lopes- Araújo, L. Santos-Sacramento, P.Y. Takeda, B.M. Macchi,

J.L.M. Nascimento, C.S.F. Maia, R.R. Lima, G.P. Arrifano, Envrionment International, 2021, v. 164, p. 1 -11.

[2] Y. Susuki, M. Kondo, H. Akiyama, Y. Ogra, Environmental Pollution, 2022, v. 307, p. 1 -11.

[3] M. Wiech, A. M. Beinfait, M. Silva, J. Barre, V. Sele, M. Bank, S. Bérail, E. Tessier, D. Amouroux, A. M. Azad, Envrionmental Pollution, 2022, v. 473, p. 1 – 11.

[4] L. Paton, T.T. Moro, T. Lockwood, T.A. Maranhão, G. Gossler, D. Classes, J. Feldmann, Environmental Science: Nano, 2024, v.11, p. 1757-2290.

[5] K. El Hanafi, B. Gomez-Gomez, Z. Pedrero, P. Bustamante, Y. Cherel, D. Amouroux, Y. Madrid, Analytica Chimica Acta, 2023, v. 1250, p. 340952.