The role of non-commercial fish in incorporating toxic elements into the trophic web in the lagoons of the southern Baltic Sea

Due to intensive human activity, especially in the second half of the 20th century, a significant amount of chemical elements has been extracted from the Earth's natural deposits. Some of these elements have no beneficial role in living organisms and are toxic. Ideally, such toxic elements would not be present in our natural environment. However, this is not the case, nor will it ever be, as these elements naturally occur on our planet and have been further introduced into the ecosystem through industrial use. There are also chemical elements that are essential or even necessary for the proper development of animal and plant organisms. However, at elevated concentrations, these elements become highly toxic. Thanks to regulations introduced in many European countries at the turn of the 20th and 21st centuries, emissions of toxic elements from anthropogenic sources have significantly decreased. Nevertheless, their concentrations in the natural environment have not declined proportionally. It is therefore crucial to understand their pathways and circulation in the environment, particularly in marine ecosystems, as fish and seafood often serve as key sources of these elements for humans. While numerous scientific studies have examined the concentrations of toxic elements (e.g., Hg, Pb, Cd, Zn, Cu, As, Se) in sediments and commercially significant fish species, there is a notable lack of data on their transfer through individual links in the trophic network, especially among small, non-commercial fish. Moreover, there is limited information in the scientific literature regarding the concentrations of technology-critical elements, some of which are or could potentially be highly toxic to living organisms. The purpose of this research is to investigate the role of small, non-commercial fish in the transfer of toxic elements within the marine trophic network, using the southern Baltic Sea as a case study. The Puck Lagoon has been selected as the research area.