Trace and rare earth elements compounds present in the marine environment are mainly transferred through the diet of organisms. Given the significance of seafood as a source of essential nutrients to humans and the diverse health risks associated with imbalances of these elements, it becomes crucial to measure their concentrations on the organisms.
The Antarctic toothfish (Dissostichus mawsoni), a long-lived top predator in the Southern Ocean, is captured annually in the region. Due to its biological and ecological features, D. mawsoni is susceptible to accumulate high concentrations of trace elements, making it a potential bioindicator for the concentrations of trace and rare earth elements in the deep-sea ecosystem of the Southern Ocean.
Considering the commercial interest of D. mawsoni, in this study the authors discuss how this species can be a good source of nutrients to consumers by also exploring if the different trace elements can be used to determine the origin of the fish. To accomplish this, it was determined for the first time the concentration of 27 trace and rare earth elements in muscle samples of the species D. mawsoni, which was caught in three areas of the Amundsen and Dumont D’Urville Seas in Antarctic (Figure 1).
As expected, the study revealed that major essential elements, particularly potassium (K), exhibited the highest concentrations, while rare earth elements registered the lowest levels in the D. mawsoni muscle. Notable differences were observed between the study areas, indicating that the concentration of these elements in this species varies geographically and within adjacent fishing areas, with highest levels identified in fish from the Amundsen Sea slope. The authors suggested that these disparities may be linked to dietary variations, differences in Southern Ocean water composition and contrasting trends in environmental changes that influence the input of some elements into the environment.
Additionally, by using otolith  lengths as a proxy for fish size and δ15N  values as an indicator of trophic position, the study found no evidence of bioaccumulation of those elements in the muscle of D. mawsoni. Instead, concentrations tended to decrease with fish size, suggesting potential influences from a growth dilution effect, metabolic and lipid content variations between younger and older fish, or habitat-related factors. Moreover, the absence of significant correlations with δ15N values indicates no biomagnification  potential within these food webs.
The later evaluation of the potential detoxification role of selenium (Se) for Mercury (Hg) in D. mawsoni was significant, specifically when mercury concentrations reach levels that could be harmful to the organism. This implies that selenium might play a crucial role in protecting the Antarctic toothfish from the adverse effects of elevated levels of Hg.
Thereby, according to these findings, D. mawsoni not only stands out as a bioindicator for the concentrations of the different trace and rare earth elements in the Southern Ocean, but also reveals itself as a good source of major essential elements to humans with concentrations of major essential elements above some of other marine fish worldwide.
 Otholits: Hard, calcium carbonate structures located directly behind the brain of bony fishes.
 δ15N: Nitrogen stable isotope, which allows for an estimation of the trophic position of consumers in a diet chain.
 Biomagnification: Increase in concentration of a substance in the tissues of organisms at successively higher levels in a food chain.
Reference: Queirós, J. P., Machado, J. F., Pereira, E., Bustamante, P., Carvalho, L., Soares, E., Stevens, D. W., & Xavier, J. C. (2023). Antarctic toothfish Dissostichus mawsoni as a bioindicator of trace and rare earth elements in the Southern Ocean. Chemosphere, 321, 138134. https://doi.org/10.1016/j.chemosphere.2023.138134
Author: Maria Soares