Insights on the accumulation and biomagnification of priority hazardous contaminants in anadromous fish from a European UNESCO Biosphere reserve area

Determining the level of contamination in the pontic shad ( Alosa immaculata) is an important aspect because the anadromous species represents a quality bioindicator of the most international river basin in the world, the Danube-Black Sea. This type of investigation is particularly necessary due to the existence of a limited database on the cumulative presence of pesticides, trace metals, and oxidative stress in such samples. To address this knowledge gap, we evaluate the concentration levels of trace metals and essential elements (Cd, Pb, Hg, Ni, Cr, Co, Cu, Mn, Fe, Zn, As), organochlorine, and organophosphorus pesticides in the muscle tissue and in the gastrointestinal content of the migratory fish species Alosa immaculata . Trace metals and essential elements were determined using ICP-MS and TXRF; pesticides were determined using an integrated QuEChERS-GC-MS/MS, while oxidative stress biomarkers were analysed with spectrophotometric methods. Lead concentrations in the edible tissue of Alosa immaculata recorded values above the EU legislation regulating maximum levels of contaminants in foods. Oxidative stress indicators (catalase, superoxide dismutase, glutathione S-transferase, glutathione reductase, and acetylcholinesterase, together with malondialdehyde levels, total antioxidant capacity) exhibited a positive correlation with pesticides. Dichlorodiphenyltrichloroethane, its metabolites and lindan isomers seem to generate an increase in reactive oxygen species. The biomagnification factor was calculated for the targeted contaminants, and the results obtained for Hg, Cd, Pb, and DDT suggest a potential ecological risk. Overall, the accumulation and biomagnification study of priority contaminants in pontic shad provides valuable insights into evaluating ecological status and supporting conservation strategies in the Danube–Black Sea basin.