Accumulation of trace elements in harbour porpoises and their selected helminths: a study from the North Sea and the Baltic Sea.

Marine ecosystems are increasingly affected by anthropogenic stressors, including pollution with trace elements. Trace elements (TE) can bioaccumulate or in some cases biomagnify along the food chain, which can have harmful consequences for marine organisms. In recent years, fish parasites emerged as complementary bioindicators due to their ability to accumulate significantly higher concentrations of certain elements than their host or other established free-living bioindicators. As top predators, marine mammals are known to accumulate high TE levels. Thus, extending this approach to marine mammal host-parasite systems offers a promising, yet underexplored, approach for biomonitoring. Therefore, in this study we analysed the concentrations of eleven TE (Ag, As, Cd, Co, Cu, Fe, Mn, Pb, Sn, Sr and Zn) in harbour porpoises and their helminths, with a particular focus on nematodes. Our findings revealed that certain elements such as Fe, Mn, Zn, As, Co and Cd were accumulated to a higher degree in parasites than in host tissues. Additionally, differences in accumulation patterns were found between parasite groups and between individuals from the North Sea and Baltic Sea. The accumulation of TE in host tissue was influenced by a number of factors, including region and helminth infection.